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New Sm–Nd, Rb–Sr, U–Pb and Hf isotope systematics for the southern Prince Charles Mountains (East Antarctica) and its tectonic implications
... Санкт-Петербург, Россия) и ФГБУ "ВНИИОкеангеология" (г. Санкт-Петербург, Россия), а также было осуществлено дополнительное посещение массива Стинир, расположенного в 10 км к востоку от массива Раймилл [47,48,[56][57][58]. ...
... Мензис не проводилось, современные публикации отсутствуют и к í àстоящему времени установлен возраст гнейсов только соседствующей к северу г. Бейлисс, к оторый отвечает границе мезо-неоархея 2822 ± 1 7 млн лет [48]. ...
... ТЕКТОНИКА И МЕТАМОРФИЗМ В регионе исследования широко представлены как пликативные, так и дизьюктивные дислокации, обладающие многообразием структурноморфологических типов, и относящиеся к нескольким разновозрастным этапам метаморфизма, соотносимым по возрасту с архейскими и протерозойскими тектоно-термальными событиями [33,48,58]. ...
Принята к публикации 30.09.2022 г.
В статье представлены комплексные результаты интерпретации структурно-петрологических исследований, новых геохимических, изотопно-геохронологических данных метаморфических и метаинтрузивных образований палеоархейского заложения горных объектов Раймилл и Блумфилд в северной части Рукерской гранит-зеленокаменной области (Горы Принс-Чарльз, Восточная Ан-тарктида). Выявлена детальная последовательность смены архейских тектоно-магматических про-цессов в северном блоке Рукерской области, а также показаны главные этапы тектонических дефор-маций и метаморфизма в ходе геодинамической эволюции докембрия, что является ключом к по-ниманию истории геологического развития архейских метаморфических комплексов Восточной Антарктики и древних регионов Земли. Северную часть Рукерского террейна слагают мезо-неоар-хейские гранито-гнейсовые купола, тектонически обрамленные фрагментами зеленокаменного по-яса мезо-неоархейской метавулканогенно-осадочной серии Мензис. Разобщенные блоки или па-кеты пластин метавулканогенно-осадочных толщ представляют собой разрез преимущественно слабометаморфизованных средне-кислых песчаников, кварцитов и слюдистых сланцев. Совокуп-ность представленных горных пород охватывает значительный интервал времени от 3.2 до 2.5 млрд лет. Состав мезоархейских гранито-гнейсовых куполов серии Моусон (3.2-3.1 млрд лет) отвечает древним гранитоидам, близок тоналит-трондьемит-гранодиоритовым (ТТГ) комплексам и сопо-ставим с аналогичными ассоциациями древних кратонов Австралии, Канады и Фенноскандии. По-роды серии Моусон являются полиметаморфическими, значительная степень их перекристаллиза-ции связана с мезоархейским этапом метаморфизма, время завершения которого соотносится с об-разованием впервые выделенных автором мезо-неоархейских блоков гранито-гнейсового купола ТТГ ассоциации с возрастом ~2.8 млрд лет. По оболочкам изученных цирконов ТТГ гнейсов опре-делåн возраст ярко проявленного тектоно-термального события ~2.7 млрд лет. Ортогнейсы серии Моусон и ТТГ гнейсы сопоставляются с внутриплитными гранитоидами А-типа и отнесены к раз-новидности низкотитанистых, существенно калиевых архейских гранитоидов. Геохимический ана-лиз состава пород показал, что образование первичных расплавов мезоархейских ортогнейсов Моусон происходило в коре на меньших глубинах (Р < 8-10 кбар) в сравнении с мезо-неоархейски-ми ТТГ гнейсами, формирование которых возможно определялось увеличением мощности коры, сменившееся ее растяжением и утонением на рубеже ~2.5 млрд лет. Ключевые слова: Восточная Антарктида, тектоника, геохронология архея, гранито-гнейсовые купола, зеленокаменные пояса, ТТГ ассоциации, рифтогенез, плюм-литосферное взаимодействие
... Bloomfield [22]. Complex on-land geological studies of the mountains were conducted during the 60th Russian Antarctic Expedition [47,48,[56][57][58]. ...
... Menzies, no present-day publications are available, and only the age of gneisses of adjacent Mt. Bayliss from the north (a boundary of the Meso-Neoarchean of 2822 ± 17 Ma) has been identified [48]. ...
... Both plicative and disjunctive dislocations of diverse structural-morphological types, which belong to several stages of metamorphism comparable by the age with the Archean and Proterozoic tectonothermal events, are abundant in the studied region [33,48,58]. ...
Abstract—
This paper presents a complex interpretation of structural–petrological studies and new geochemical and isotope–geochronological data on the Paleoarchean metamorphic and metaintrusive rocks of Mts. Rymill and Bloomfield in the northern part of the granite-greenstone Ruker terrane (Prince Charles Mountains, East Antarctica). The detailed sequence of changing Archean tectonomagmatic processes in the northern block of the Ruker area has been revealed and the main stages of tectonic deformations and metamorphism of Precambrian geodynamic evolution are shown, which is a key for the understanding of the geological evolution of the Archean metamorphic complexes of East Antarctica and ancient Earth’s regions. The northern part of the Ruker Terrane is composed of the Meso-Neoarchean granite–gneiss domes, which are tectonically framed by fragments of greenstone belt of the metavolcanosedimentary Meso-Neoarchean Menzies Series. The detached blocks or packages of sheets of metavolcanosedimentary sequences are a section of weakly metamorphosed intermediate–felsic sandstones, quartzites, and micaceous schists. An assemblage of rocks spans a significant period from 3.2 to 2.5 Ga. The composition of the Mesoarchean granite–gneiss domes of the Mawson Series (3.2–3.1 Ga) corresponds to those of ancient granitoids, is similar to tonalite–trondhjemite–granodiorite (TTG) complexes, and is comparable with similar associations of ancient cratons of Australia, Canada, and Fennoscandia. The rocks of the Mawson Series are polymetamorphic and a significant part of their recrystallization is related to the Mesoarchean stage of metamorphism, whose end is comparable with the formation of the Meso-Neoarchean blocks of the granite–gneiss association of the TTG dome of ~2.8 Ga identified by the author. The age of the striking tectonothermal event of ~2.7 Ga is determined by overgrowths of zircons from the TTG gneisses. The Mawson Orthogneiss and TTG gneisses are compared with intraplate A‑granitoids and are ascribed to low-Ti high-K Archean granitoids. The geochemistry of the rocks indicates that primary melts of the Meso-Archean Mawson Orthogneiss formed in crust at shallower depths (P < 8–10 kbar) in comparison with Meso-Archean TTG gneisses, whose formation is possibly caused by the increasing thickness of the crust followed by its extension and thinning at a boundary of ~2.5 Ga.
... The Ruker Province is largely a medium-grade terrain which experienced major tectonothermal events at ca 3400-3160 Ma, 2800-2700 Ma, 2500 Ma, and 2100-2000 Ma (the Lambert Orogeny); with rare evidence for a ca 1750 Ma event (Boger et al., 2006;Corvino et al., 2008;Mikhalsky et al., 2006bMikhalsky et al., , 2009Mikhalsky et al., , 2010. Palaeoproterozoic (ca 2500-2000 Ma) rocks in the northern part of the Ruker Province are designated the Lambert Complex (Mikhalsky et al., 2006b;Phillips et al., 2009). ...
... Stinear, and Mt. Rymill (Alexeev et al., 2019;Boger et al., 2006;Mikhalsky et al., 2006bMikhalsky et al., , 2010. In these localities ca 2800 Ma orthogneiss protolith emplacement and ca 2700 Ma partial melting/migmatite formation events have been documented. ...
... n = xx/xx defines number of concordant analyses (D < 10; 1 analysis per grain, except A34) / total number of analyses obtained. Bars below define the major tectono-thermal events in the region (Boger et al., 2006;Liu et al., 2013Liu et al., , 2014Mikhalsky et al., 2006aMikhalsky et al., , 2006bMikhalsky et al., , 2010Mikhalsky et al., , 2013. Liu et al., 2017;Mikhalsky et al., 2013) and supports this scenario. ...
Cretaceous alkaline-ultramafic stocks in the northern Prince Charles Mountains (PCM) contain zircon xenocrysts entrained during magma ascent to the surface. These xenocrysts provide the only evidence for the age of the underlying crustal rocks in the area. The zircons display a range of ages from ca 2700 Ma to ca 300–260 Ma, with the most dominant ages of ca 900–800 Ma and ca 660–500 Ma. These data indicate that the presently exposed ca 1000–950 Ma metamorphic rocks in the northern PCM are underlain by other geological unit(s). The presence of ca 2700 Ma zircons indicates that a Neoarchaean component is present in the lower crust and that the presumed Proterozoic Rayner Province is not entirely composed of Proterozoic protoliths, but rather is a tectonic mixture of Neoarchaean and younger rocks. This finding questions a Cambrian (Kuunga-age) collisional suture running through the Ruker Province, which may thus be further south within the sub-ice terrain. Nevertheless, the presence of ca 900–800 Ma and ca 600–500 Ma zircons argue for more widespread post-1000 Ma metamorphic events than are observed at the surface. Ca 300–260 Ma zircons, which could not have been derived from any known crystalline rocks in this region, indicate within-crustal chambers parent to mafic dyke suites.
... Ga, and Vestfold Province 2.7-3.0 Ga (see Mikhalsky, 2008;Mikhalsky et al., 2006aMikhalsky et al., , 2010Mikhalsky et al., , 2013a The Ruker and the Rayner provinces are not homogeneous in their structure and composition and may be further subdivided into specific terranes (e.g., Mikhalsky et al., 2006bMikhalsky et al., , 2013a. In this work we refrain from using the term "terrane" basically due to the lack of exposed clear major crustal discontinuities between the suspect blocks and to the presence of certain shared geological features between them, albeit such features may not always be unequivocal. ...
... The southern PCM (terrain southward Mt Johns and Lawrence Hills) is known as the Ruker Complex or Ruker Province Phillips et al., 2006;Mikhalsky et al., 2010) and was divided into two domains of distinct geological history: the Ruker Terrane and the Lambert Terrane (Mikhalsky et al., 2006b), a subdivision also utilized by Boger et al. (2001). In this study we assign designation the Mawson−Stinear Zone in place of the Ruker Zone (Terrane) to avoid name mess and to emphasize the southern Mawson Escarpment and Mt Stinear are the key localities. ...
... The infrastructure comprises both orthoand paragneiss associations. Orthogneiss units are represented by ca 3400-3160 Ma Mawson Suite (orthogneiss protolith emplacement ages, 3160 Ma is also possibly an age of metamorphism; Boger et al., 2006, Mikhalsky et al., 2010 and commonly gneissose ca 3000-2800 Ma granitic plutons. Paragneiss units are represented by Mawson Group (protolith deposited in a post-3150 Ma time) and Stinear Group (protolith deposited in a post-2800 Ma time; Phillips et al., 2006, and VNIIOkeangeologia, unpublished data). ...
Explanatory notes to the Geological map of Mac-Robertson Land, Princcess Elixabeth Land and Prydz Bay in scale 1 mln
... The ca. 3200-2950 Ma granite gneiss basement of this terrane is overlain by or interleaved with deformed Proterozoic supracrustal units. While the basement orthogneissic rock (Mawson orthogneiss) with components of TTG to granitic suites, biotite-feldspar gneiss and hornblende-biotite gneiss (Mikhalsky et al., 2010) has close resemblance with the PalLahara gneiss, the sedimentary lithounits too show striking similarities with the NSB and SSB. The quartzitemica schist-dominated Menzies Group with depositional age <3200 Ma (Phillips et al., 2006) has almost identical counterpart in the Mahagiri-Mankarchua groups. ...
... In East Antarctica, these two sequences are separated by the ca. 2800 Ma Stinear orogeny (Mikhalsky et al., 2010) which is equivalent to the ca. 2800 Ma orogeny at the southern SC (PalLahara orogeny). ...
... Interestingly, Fisher Terrane and Beaver Terrane of the Rayner Province lying adjacent to the Ruker Terrane also show detrital zircon signatures of ca. 2800-2500 Ma, 2200-2100 Ma and 1900-1700 Ma (Mikhalsky et al., 2010). These analogies allow us to conceive a vast circum-cratonic Paleoproterozoic belt surrounding the Ruker Terrane, Napier Complex, SC, BC and DC (Fig. 13). ...
Singhbhum Craton (>3500 Ma), the Archean continental nuclei of eastern India, preserves on its southern margin coexisting deep crustal granulites and shallow crustal metasedimentary lithologic units that were juxtaposed through complex transpressional tectonics. U-Pb detrital zircon ages were obtained from five samples of widely separated locations of two parallel belts, which are known as the Northern and the Southern Supracrustal Belts. In addition, zircon grains from a pegmatite from the central gneissic complex were also dated. The LA-ICP-MS derived U-Pb age data from these samples lead to the estimation of age of sedimentation and the thermal events in the provenance. The U-Pb age from these samples yielded younger than 2235 ± 28 Ma for Northern Supracrustal Belt, while that of the Southern Supracrustal Belt is consistently younger (<1835 Ma). Development of these basins at the southern margin of the Singhbhum Craton was associated with four cycles of sedimentation at ca. 3100-2800 Ma, ca. 2800-2450 Ma, ca. 2450-2235 Ma and ca. 2235-1835 Ma. These cycles resulted in the southward growth of the Singhbhum Craton through successive opening and closing of basins. The ca. 2540-2480 Ma zircon population of the Northern Supracrustal Belt has no proven source from the Singhbhum Craton, but distal cratonic blocks might have provided the detritus. The provenance of the sediments could also be traced in the transcontinental pre-existing cratonic block, e.g. East Antarctica.
... Key crust-forming igneous and metamorphic events between ca. 2.5 and 1.7 Ga are now well recognized in the central Transantarctic Mountains (Bennett and Fanning, 1993;Goodge and Fanning, 1999;Goodge et al., 2001), southern Prince Charles Mountains (e.g., Boger et al., 2006Boger et al., , 2008Mikhalsky et al., 2006Mikhalsky et al., , 2010, and the Shackleton Range (e.g., Pankhurst et al., 1983;Helper et al., 2000;Will et al., 2009) of Antarctica, further enhancing their inclusion in an extensive Mawson province. Gneisses from the Miller Range with ages of 3150-3050 Ma (Bennett and Fanning, 1993) were thought to record the earliest events in the Mawson Continent, but at the time were not recognized in Terre Adélie or the Gawler Craton. ...
... Signatures of 3.1, 2.5 and 1.7 Ga crustal events are well known from elsewhere in East Antarctica (Fig. 22). U-Pb geochronology has demonstrated $3.1 Ga magmatism in other areas of Antarctica, including the Denman Glacier area of the Bunger Hills Sheraton et al., 1993), the Ruker Complex in the southern Prince Charles Mountains (Boger et al., 2006(Boger et al., , 2008Mikhalsky et al., 2006Mikhalsky et al., , 2010, the Napier Complex in Enderby Land (Sheraton et al., 1987), and along the Mawson Coast (Grew et al., 1988). Among these, the Denman Glacier area has a notably similar history to the Nimrod Complex. ...
... Time periods of major supercontinent existence shown on right side, and orogenic activity noted by colored horizontal bars. Sources: (a) Goodge and Fanning (1999), Goodge et al. (2001, this paper); (b) Goodge et al. ( , 2004Goodge et al. ( , 2008, this paper), Wysoczanski and Allibone (2004); (c) Goodge et al. (2008Goodge et al. ( , 2012Goodge et al. ( , 2013, Nissen et al. (2013); (d) Oliver and Fanning (1997), Peucat et al. (1999Peucat et al. ( , 2002, Ménot et al. (1999), Duclaux et al. (2007Duclaux et al. ( , 2008, Carson (2011); (e) Black et al. (1992), Sheraton et al. (1992Sheraton et al. ( , 1993Sheraton et al. ( , 1995; (f) , Will et al. (2009Will et al. ( , 2010; (g) Boger et al. (2006Boger et al. ( , 2008, Mikhalsky et al. (2006Mikhalsky et al. ( , 2010; (h) Daly et al. (1998), Fairclough et al. (2003, Swain et al. (2005), Fraser and Lyons (2006, Hand et al. (2007), Payne et al. (2009); (i) Bennett and DePaolo (1987), Wooden and Miller (1990), Gleason et al. (1994), Barth et al. (2000Barth et al. ( , 2009, Rämö et al. (2003), Shufeldt et al. (2010), Strickland et al. (2013), Wooden et al. (2013); (j) Doughty and Chamberlain (2008), Zirakparvar et al. (2010), Nesheim et al. (2012; (k) Barth et al. (2009), Gehrels et al. (2011 mafic magmatic underplating associated with lithospheric thinning. Other isolated outcrops contain $1650 Ma migmatites and $1600 Ma granitoids (Duclaux et al., 2007). ...
... The Lambert Terrane contains granitic-granodioritic orthogneisses with major protolith ages of ca. 2.4 and 2.1 Ga (Mikhalsky et al., 2006a(Mikhalsky et al., , 2010Corvino et al., 2008), and metasedimentary rocks that were deposited in the late Archean to early Palaeoproterozoic (Phillips et al., 2006). The Ruker Terrane consists of the Archean Ruker Complex, which records major igneous events at ca. 3.2 and 2.8 Ga (Boger et al., 2006;Phillips et al., 2006;Mikhalsky et al., 2006aMikhalsky et al., , 2010, and overlying greenschist-to amphibolite-facies supracrustal sequences of various ages groups. ...
... 2.4 and 2.1 Ga (Mikhalsky et al., 2006a(Mikhalsky et al., , 2010Corvino et al., 2008), and metasedimentary rocks that were deposited in the late Archean to early Palaeoproterozoic (Phillips et al., 2006). The Ruker Terrane consists of the Archean Ruker Complex, which records major igneous events at ca. 3.2 and 2.8 Ga (Boger et al., 2006;Phillips et al., 2006;Mikhalsky et al., 2006aMikhalsky et al., , 2010, and overlying greenschist-to amphibolite-facies supracrustal sequences of various ages groups. ...
... In the Rauer Group, tonalitic orthogneisses formed during the periods 3470-3270 Ma and 2840-2800 Ma, with Nd model ages (T DM Nd ) between 3.8 and 3.5 Ga (Sheraton et al., 1984;Kinny et al., 1993;Harley et al., 1998). In the Ruker Terrane, tonalitic-trondhjemitic-granitic orthogneisses were emplaced at 3390-3150 Ma and then underwent greenschist to amphibolite facies metamorphism and syntectonic granitic intrusion at 2820-2780 Ma (Boger et al., 2001(Boger et al., , 2006Mikhalsky et al., 2006aMikhalsky et al., , 2010. The corresponding T DM Nd ages range from 3.8 to 2.7 Ga (Mikhalsky et al., 2006b). ...
... The Ruker Province of sPCM comprises two juxtaposed blocks: the Ruker Terrane and the Lambert Terrane (Kamenev et al. 1993;Boger et al. 2001;Mikhalsky et al. 2006). The Archaean tonalitic-trondhjemitic gneisses forming the~3500 Ma Mawson Suite are the oldest recognizable units of the Ruker Terrane (Boger et al. 2006;Mikhalsky et al. 2006Mikhalsky et al. , 2010. The xenocrystic zircons from these orthogneisses indicate the age of these gneisses to be~3170 Ma (weighted mean Pb-Pb age of 3177 ± 6 Ma, Boger et al. 2006), and the model ages range from 3900 to 3400 Ma (Mikhalsky et al. 2006). ...
... The age limits of deformation of the Ruker Terrane are provided by a concordant Pb-Pb age of 2788 ± 5 Ma zircons from syntectonic plutons and a weighted mean Pb-Pb age of 2645 ± 5 Ma obtained from post-tectonic pegmatites cutting across the layered gneisses (Boger et al. 2006). The Nd isotope depleted mantle model ages (after DePaolo 1988) of the Ruker Terrane also show three different protoliths for the basement gneisses: 3600-3800 Ma and 3200-3400 Ma for the Palaeoarchaean gneisses and 2700-3000 Ma for the Mesoarchaean gneisses (Mikhalsky et al. 2010). A metagabbro of the Ruker Terrane has a weighted mean U-Pb zircon age of 3120 ± 13 Ma, but a 3145 ± 12 Ma upper intercept age of another group of samples is interpreted to be the crystallization at~3150 Ma (Mikhalsky et al. 2010). ...
... The Nd isotope depleted mantle model ages (after DePaolo 1988) of the Ruker Terrane also show three different protoliths for the basement gneisses: 3600-3800 Ma and 3200-3400 Ma for the Palaeoarchaean gneisses and 2700-3000 Ma for the Mesoarchaean gneisses (Mikhalsky et al. 2010). A metagabbro of the Ruker Terrane has a weighted mean U-Pb zircon age of 3120 ± 13 Ma, but a 3145 ± 12 Ma upper intercept age of another group of samples is interpreted to be the crystallization at~3150 Ma (Mikhalsky et al. 2010). The basement gneisses and the ultramafic rocks are interpreted to be derived from a depleted mantle source 3400-3800 Ma (Mikhalsky et al. 2010). ...
An Archaean continent ‘SIWA’, an acronym for South India – Western Australia, comprising the Bastar–Dharwar craton, the Yilgarn craton, the Napier complex and the Vestfold Hills has been identified from palaeomagnetic and spatio-temporal data. This assembly was dispersed in three phases with development of the proto-Indian ocean. The first and second events at ~2350 Ma and ~2000 Ma were related to the separation of the Yilgarn craton, and the Napier Complex, respectively, to form a proto Indo-Antarctic ocean and the Cuddapah basin. The proto-ocean was closed at ~1650 Ma by the collision of the Lambert terrane of East Antarctica and the Bastar–Dharwar craton. This collision associated with ultra-high temperature granulite facies metamorphism is identified in the southern domain of the Eastern Ghats and the Oygardens domain of the East Antarctica. The third extensional event between 1500 and 1200 Ma was associated with the separation of the Vestfold Hills block and a second phase of opening of the proto-Indian ocean, and development of a series of basins on the western side of the Eastern Ghats (the Chhatisgarh, Khariar, Ampani, Indravati and Sabari basins). The closing of this ocean basin during the Eastern Ghats–Rayner orogeny at ~950 Ma was related to the amalgamation of India and East Antarctica to form the supercontinent Rodinia. During Neoproterozoic, this part of Rodinia was involved in orogenic collapse/extension, and deposition of the Sodruzhesvo Group. The Pan-African Prydz Bay orogeny at ~550 Ma caused closing of the basin to form the East Gondwana Land.
... The Ruker Complex, the focus of this study, comprises an Archaean granite^gneiss basement defined by the Mawson Suite and Menzies Group, together with two or more sequences of sedimentary and volcanic cover rocks (Ravich et al., 1985;Kamenev et al., 1993;Mikhalsky et al., 2001;Phillips et al., 2009). The Mawson Suite consists of well-dated felsic intrusions that were emplaced at 3390^3380 Ma and 3180^3160 Ma (Boger et al., 2006Mikhalsky et al., 2006aMikhalsky et al., , 2010. The Menzies Group consists of thick horizons of quartzite intercalated with rocks of volcanic, terrigenous, and chemical origin. ...
... Metamorphism is dated at 2780 Ma from the southern Mawson Escarpment (Boger et al., 2006), whereas syntectonic granitic intrusions (c. 2815 Ma) are known from Mts Stinear, Bayliss and Rymill (Mikhalsky et al., 2010). ...
... Compositional variations in the mantle source, fractional crystallization and/or assimilation processes may be responsible for the observed chemical heterogeneity. In addition, the poor correlation between Zr and mg number (Fig. 13a) suggests that the compositional variations may also be due to varying degrees of partial melting: a lower (Mikhalsky et al., 2010); fine long-dash lines, meta-gabbro^dolerites in Ruker Group (E. V. Mikhalsky, unpublished data); bold short-dash line, NNE-trending mafic dykes in the southern Mawson Escarpment . ...
Mafic dykes are a characteristic geological feature of the Ruker Complex in the southern Prince Charles Mountains. We present new geological, geochemical, and Sm-Nd isotopic data for these rocks, which place constraints on their genesis, mantle sources, and relative timing, as well as providing a substantial basis for a comparison between these intrusions and similar rocks from other Archaean terranes of East Antarctica. The oldest of the intrusions form dykes composed of distinctive rocks rich in Mg, Cr, and Ni. These rocks were probably derived via varying degrees of partial melting of a metasomatically enriched and radiogenic mantle source at relatively shallow mantle levels. Younger and volumetrically more significant dykes are composed of subalkaline tholeiite. These tholeiitic dykes strike ENE, NW or NNE and can be divided into two geochemically distinct subgroups: a low-LILE (large ion lithophile element) group (mostly the NNE-trending dykes) and a high-LILE group (NW-trending and partly other directions). The low-LILE group rocks originated from an enriched mid-ocean ridge basalt-like source and are characterized by relatively young Sm-Nd T-DM model ages between 1 center dot 9 and 2 center dot 4 Ma. The high-LILE group rocks have higher LILE/HFSE (high field strength element) ratios, which imply derivation from an enriched subcontinental mantle source. These rocks have generally older T-DM model ages between 2 center dot 3 and 3 center dot 8 Ga and display geochemical similarities to mafic metavolcanic rocks found within the Palaeoproterozoic Ruker Group, a cover sequence to the Archaean Ruker Complex. As was observed by earlier researchers, the subalkaline tholeiitic dykes in the Ruker Complex have many compositional features in common with mafic dykes from the Napier Complex of Enderby Land and from the Vestfold Hills. However, our data do not provide convincing evidence for a direct correlation with these dyke suites. The youngest phase of mafic intrusions comprises distinctive high-Ti-P rocks that occur as sills within the Neoproterozoic Sodruzhestvo Group, another cover sequence to the Ruker Complex. The high-Ti-P rocks do not correlate with any of the dyke suites observed within the Ruker Complex, nor from elsewhere in East Antarctica. They are interpreted to represent manifestations of plume-related magmatism associated with extension, subsidence, and accumulation of the Sodruzhestvo Group.
... Boger et al. (2001) interpreted this as a major Pan-African suture zone that extends east -west across the southern Prince Mountains, consistent with a lack of evidence for the c. 1.0 Ga metamorphism in the Ruker Complex basement. However, more recent geochronology indicates that the Ruker and Lambert complexes further west do not have a simple outcrop pattern (Phillips et al. 2006;Mikhalsky et al. 2010), and has also identified 3.2 Ga detrital zircon grains in one of the sedimentary sequences that lost Pb at 990-900 Ma (Phillips et al. 2006), consistent with a Rayner overprint on Ruker material. Thus, while Boger (2011) has continued to argue for a c. 0.5 Ga suture in the southern Prince Charles Mountains, others have proposed that these terranes assembled at c. 1.0 Ga and that their boundaries were reactivated at c. 0.5 Ga in response to collisional tectonics elsewhere Mikhalsky et al. 2010). ...
... However, more recent geochronology indicates that the Ruker and Lambert complexes further west do not have a simple outcrop pattern (Phillips et al. 2006;Mikhalsky et al. 2010), and has also identified 3.2 Ga detrital zircon grains in one of the sedimentary sequences that lost Pb at 990-900 Ma (Phillips et al. 2006), consistent with a Rayner overprint on Ruker material. Thus, while Boger (2011) has continued to argue for a c. 0.5 Ga suture in the southern Prince Charles Mountains, others have proposed that these terranes assembled at c. 1.0 Ga and that their boundaries were reactivated at c. 0.5 Ga in response to collisional tectonics elsewhere Mikhalsky et al. 2010). ...
... Two possible paths have been proposed for a Pan-African orogen linking the Prydz-Denman region to the Shackleton Range. Boger et al. (2001), Boger & Miller (2004) and Boger (2011) suggested it might pass through the inferred suture between the Ruker and Lambert complexes in the southern Prince Charles Mountains (path PD1 in Fig. 6b), although others have argued that this suture formed at c. 1.0 rather than 0.5 Ga Mikhalsky et al. 2010). Fitzsimons (2003) suggested an alternative path (path PD2 in Fig. 6b) that passes under the ice between the southern Prince Charles Mountains and the Gamburtsev Subglacial Mountains, an enigmatic and unexposed mountain range approximately 500 km south of the Prince Charles Mountains (Figs 2 & 6). ...
The Antarctic rock record spans some 3.5 billion years of history, and has made important contributions to our understanding of how Earth's continents assemble and disperse through time. Correlations between Antarctica and other southern continents were critical to the concept of Gondwana, the Palaeozoic supercontinent used to support early arguments for continental drift, while evidence for Proterozoic connections between Antarctica and North America led to the ‘SWEAT’ configuration (linking SW USA to East Antarctica) for an early Neoproterozoic supercontinent known as Rodinia. Antarctica also contains relicts of an older Palaeo- to Mesoproterozoic supercontinent known as Nuna, along with several Archaean fragments that belonged to one or more ‘supercratons’ in Neoarchaean times. It thus seems likely that Antarctica contains remnants of most, if not all, of Earth's supercontinents, and Antarctic research continues to provide insights into their palaeogeography and geological evolution. One area of research is the latest Neoproterozoic–Mesozoic active margin of Gondwana, preserved in Antarctica as the Ross Orogen and a number of outboard terranes that now form West Antarctica. Major episodes of magmatism, deformation and metamorphism along this palaeo-Pacific margin at 590–500 and 300–230 Ma can be linked to reduced convergence along the internal collisional orogens that formed Gondwana and Pangaea, respectively; indicating that accretionary systems are sensitive to changes in the global plate tectonic budget. Other research has focused on Grenville-age (c. 1.0 Ga) and Pan-African (c. 0.5 Ga) metamorphism in the East Antarctic Craton. These global-scale events record the amalgamation of Rodinia and Gondwana, respectively. Three coastal segments of Grenville-age metamorphism in the Indian Ocean sector of Antarctica are each linked to the c. 1.0 Ga collision between older cratons but are separated by two regions of pervasive Pan-African metamorphism ascribed to Neoproterozoic ocean closure. The tectonic setting of these events is poorly constrained given the sparse exposure, deep erosion level and likelihood that younger metamorphic events have reactivated older structures. The projection of these orogens under the ice is also controversial, but it is likely that at least one of the Pan-African orogens links up with the Shackleton Range on the palaeo-Pacific margin of the craton. Sedimentary detritus and glacial erratics at the edge of the ice sheet provide evidence for the c. 1.0 and 0.5 Ga orogenesis in the continental interior, while geophysical data reveal prominent geological boundaries under the ice, but there are insufficient data to trace these features to exposed structures of known age. Until we can resolve the subglacial geometry and tectonic setting of the c. 0.5 and 1.0 Ga metamorphism, there will be no consensus on the configuration of Rodinia, or the size and shape of the continents that existed immediately before and after this supercontinent. Given this uncertainty, it is premature to speculate on the role of Antarctica in earlier supercontinents, but it is likely that Antarctica will continue to provide important constraints when our attention shifts to these earlier events.
... 35.1 and 35.2) is widely regarded as representative of a larger region of the "inboard" EAS that collided or interacted with outboard terranes (e.g., the Archean Napier Complex) and other shield areas (e.g., the Dharwar and Bastar cratons of India) at 990-910 and 550-500 Ma (e.g., Fitzsimons, 2000b;Boger and Miller, 2004). It comprises a polyphase Archean (c.3390-3155 Ma) granite gneiss basement, the Mawson Orthogneiss Suite ( Fig. 35.3A), tectonically interleaved with deformed metasedimentary and metavolcanic rocks (Fig. 35.3B;Tingey, 1982Tingey, , 1991Mikhalsky et al., 2001Mikhalsky et al., , 2010Boger et al., 2006;Mikhalsky et al., 2006a). ...
... Homogeneous/massive gneissic granites (Mawson Orthogneiss Suite), which crop out in the Southern Mawson Escarpment, preserve oscillatory zoned magmatic zircons that record crystallization over the time interval c.3185-3145 Ma (Mikhalsky et al., 2006a(Mikhalsky et al., , 2010 or 3177-3160 Ma (Boger et al., 2006). One of these granitoids preserves evidence for older crustal sources in the form of xenocrystic zircon cores with a weighted population concordia age of 3370 ± 11 Ma (Boger et al., 2006). ...
... One of these granitoids preserves evidence for older crustal sources in the form of xenocrystic zircon cores with a weighted population concordia age of 3370 ± 11 Ma (Boger et al., 2006). This age is consistent with the incorporation of crustal sources similar to those represented by a Y-depleted trondhjemitic gneiss occurring near McCue Bluff in the southern Mawson Escarpment (3377 ± 9 Ma; zircon U-Pb) and a porphyritic tonalite cobble preserved in Ruker Series metasediments at Mount Rubin (3392 ± 6 Ma; zircon U-Pb) (Mikhalsky et al., 2006a(Mikhalsky et al., , 2010. These results demonstrate that the Ruker Terrane contains crustal components at least as old as c.3390 Ma, and on the basis of Sm-Nd model ages (T DM ) of c.3200-3900 Ma (Mikhalsky et al., 2006b), it is possible that even more ancient early Archean precursors may be present. ...
This chapter describes the various aspects of the East Antarctic shield. The East Antarctic Shield comprises most of the main landmass of Antarctica, bounded by the Transantarctic Mountains and the Southern Ocean in the sector from Africa to east Australia. Despite less than 0.5% of its land area consisting of exposed rock, the East Antarctic Shield preserves a remarkable record of Earth evolution that spans in time from the earliest Archaean to the Cambrian. Temporal, structural, and metamorphic constraints from the best-studied Pan-African areas are consistent with their formation and evolution as collisional belts, with collision terminated either by late-stage extensional collapse or the lateral escape of mid-crustal domains along high-strain zones at ca. 520–500 Ma. The correlations in events and provenance ages in the metasediments have stimulated the proposal that the Mawson Block may form much of the continental landmass of East Antarctica underlying the ice, at least as far to the west as the subglacial Lake Vostok. The early archaean orthogneisses of the Mather Terrane are also elaborated in the chapter.
... Boger et al. (2001) interpreted this as a major Pan-African suture zone that extends east -west across the southern Prince Mountains, consistent with a lack of evidence for the c. 1.0 Ga metamorphism in the Ruker Complex basement. However, more recent geochronology indicates that the Ruker and Lambert complexes further west do not have a simple outcrop pattern (Phillips et al. 2006;Mikhalsky et al. 2010), and has also identified 3.2 Ga detrital zircon grains in one of the sedimentary sequences that lost Pb at 990-900 Ma (Phillips et al. 2006), consistent with a Rayner overprint on Ruker material. Thus, while Boger (2011) has continued to argue for a c. 0.5 Ga suture in the southern Prince Charles Mountains, others have proposed that these terranes assembled at c. 1.0 Ga and that their boundaries were reactivated at c. 0.5 Ga in response to collisional tectonics elsewhere Mikhalsky et al. 2010). ...
... However, more recent geochronology indicates that the Ruker and Lambert complexes further west do not have a simple outcrop pattern (Phillips et al. 2006;Mikhalsky et al. 2010), and has also identified 3.2 Ga detrital zircon grains in one of the sedimentary sequences that lost Pb at 990-900 Ma (Phillips et al. 2006), consistent with a Rayner overprint on Ruker material. Thus, while Boger (2011) has continued to argue for a c. 0.5 Ga suture in the southern Prince Charles Mountains, others have proposed that these terranes assembled at c. 1.0 Ga and that their boundaries were reactivated at c. 0.5 Ga in response to collisional tectonics elsewhere Mikhalsky et al. 2010). ...
... Two possible paths have been proposed for a Pan-African orogen linking the Prydz-Denman region to the Shackleton Range. Boger et al. (2001), Boger & Miller (2004) and Boger (2011) suggested it might pass through the inferred suture between the Ruker and Lambert complexes in the southern Prince Charles Mountains (path PD1 in Fig. 6b), although others have argued that this suture formed at c. 1.0 rather than 0.5 Ga Mikhalsky et al. 2010). Fitzsimons (2003) suggested an alternative path (path PD2 in Fig. 6b) that passes under the ice between the southern Prince Charles Mountains and the Gamburtsev Subglacial Mountains, an enigmatic and unexposed mountain range approximately 500 km south of the Prince Charles Mountains (Figs 2 & 6). ...
The East Antarctic Shield consists of a variety of Archaean and Proterozoic-Cambrian high-grade terranes that have distinct crustal histories and were amalgamated at various times in the Precambrian-Cambrian. High-grade Pan-African tectonism at 600-500 Ma is recognized from four distinct belts: the Dronning Maud Land, Lützow-Holm Bay, Prydz Bay and Denman Glacier Belts. These high-grade belts juxtapose distinct Mesoproterozoic and Neoproterozoic crustal provinces (Maud, Rayner and Wilkes), the Rauer Terrane, and have also marginally affected Archaean cratonic remnants in the Napier Complex and southern Prince Charles Mountains. The Wilkes Province experienced its principal tectonothermal events prior to 1130 Ma and was not affected by the younger events that characterize the Maud Province (1150 and 1030-990 Ma), the Rayner Province (990-920 Ma) and the Rauer Terrane (1030-990 Ma). These differences between the isotopic/event records of the basement provinces now separated by the Pan-African belts require that the older provinces were not formerly parts of a continuous 'Grenville' belt as proposed in the SW US-East Antartic model. East Antartica was not a single unified crustal block within either East Gondwana or Rodinia until the Cambrian, which is now demonstrated to be the key phase of high-grade and ultrahigh-temperature (UHT) metamorphism associated with supercontinent assembly. The high-grade Pan-African tectonism is characterized by extensive infracrustal melting, clockwise P-T paths, rapid post-peak exhumation along isothermal decompression paths to shallow-or mid-crustal levels by 500 Ma and the generation, at least locally, of UHT conditions. A significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects. Whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust, these one-dimensional models are inconsistent with present crustal thicknesses of 25-35 km in the Pan-African domains of the East Antarctic Shield.
... The Ruker Complex consists mostly of Archaean protoliths emplaced at c. 3.1-3.2 Ga and 2.8 Ga, and deformed and metamorphosed and amphibolite facies at 2.8 Ga (Mikhalsky et al. 2006b(Mikhalsky et al. , 2010Boger et al. 2006). These middle Archaean basement rocks are overlain, and now tectonically interleaved with, Late Archaean metasedimentary (≤2.5 Ga) and metavolcanic rocks (Mikhalsky et al. 2001;Phillips et al. 2006). ...
... These middle Archaean basement rocks are overlain, and now tectonically interleaved with, Late Archaean metasedimentary (≤2.5 Ga) and metavolcanic rocks (Mikhalsky et al. 2001;Phillips et al. 2006). Both the basement and the sedimentary cover rocks were then deformed during the Cambrian, associated with the intrusion of minor granitoids (Mikhalsky et al. 2010). The grade of metamorphism during the Cambrian reworking of the Ruker Complex was not high -mostly greenschist-or lower amphibolitefacies (Phillips et al. 2007a(Phillips et al. , 2007b. ...
... The affinity of the Ruker Complex is unclear. Mikhalsky et al. (2010) correlated the terrane with the Vestfold Hills and, by inference, also the Indian cratons. Phillips et al. (2006) inferred that both the Rauer Terrane (below) and the Vestfold Hills were proximal to the Ruker Complex on the basis of detrital zircon patterns from the Archaean metasediments, whereas Boger (2011) inferred that no correlative rocks exist outside Antarctica, instead suggesting that the Ruker Complex represents part of a poorly exposed Antarctic Craton (Crohn Craton), which lies towards the centre of the modern continent. ...
New feldspar lead isotope compositions of crystalline rocks from the Indian Ocean sector of East Antarctica, in conjunction with the review of data from elsewhere within the continent and from continents formerly adjacent within Gondwana, refine boundaries and evolutionary histories of terranes previously inferred from geological mapping and complementary isotope studies. Coastal Archaean Vestfold and Napier complexes have overlapping compositions and had Pb isotopes homogenized at 2.5 Ga sourced from or within already fractionated protoliths with high and variable U–Pb. Identical compositions from the Dharwar Craton of India support a correlation with these Antarctic terranes. The Proterozoic–Palaeozoic Rayner Complex and Prydz Belt yield more radiogenic compositions and are broadly similar and strongly suggest these units correlate with parts of the Eastern Ghats Belt of India. A strikingly different signature is evident from the inboard Ruker Complex, which yielded unradiogenic compositions. This complex is unlike any unit within India or Australia, suggesting that these rocks represent exposures of an Antarctic (Crohn) Craton. Compositions from the enigmatic Rauer Terrane are consistent with a shared early history with the Ruker Complex but with a different post-Archaean evolution.
Supplementary material
Feldspar LA-ICP-MS Pb isotope data are available at www.geolsoc.org.uk/SUP18622
... East Antarctica itself is primarily composed of an ancient ArcheaneProterozoic shield with a granitic basement and various types of metasedimentary rocks frequently cut by mafic dykes (2800e530 Ma) (Mikhalsky et al., 2001(Mikhalsky et al., , 2019. The well-exposed ArcheanePaleoproterozoic (Ruker Terrane) and Meso-Neoproterozoic (Rayner Terrane, including the Fisher Terrane) comprise the Prince Charles Mountains, with older to younger ages arranged from south to north (Mikhalsky et al., 2001(Mikhalsky et al., , 2010 (Fig. 1A). Dalziel (1992) described four Archean nuclei outcropping in Antarctica but did not name them. ...
... Most of the data points for the samples from core P1-2 are located within the range of the Rayner Terrane, except for seven glacial samples and one interglacial sample, which extend outside the range and toward that of the Ruker Terrane. The SreNd distribution for the samples from core P1-2 is also located in the region between the paired SreNd isotopes of charnockite from the northern Prince Charles Mountains (Zhao et al., 1997) and a few felsic or granitic gneiss rocks from the Ruker Terrane (Mikhalsky et al., 2010), again closer to the former. The Fisher Terrane is more radiogenic in ε Nd and lower in 87 Sr/ 86 Sr, separated from the entire Rayner Terrane (Fig. 7). ...
Knowledge regarding the response of the East Antarctic Ice Sheet to glacial–interglacial climatic cycles in the late Pleistocene is critical to understanding the global climate system and projections of future sea level rise. Here, we observed notable glacial–interglacial cyclicity in magnetic properties, bulk detrital Sr–Nd isotopes, and Fe/Ti ratios over the previous 530 kyr in three well-dated gravity cores from the continental rise offshore of Prydz Bay (East Antarctica). Our results show that Antarctic continental sources with more Ti-rich magnetite, less radiogenic epsilon neodymium (εNd), and higher Fe/Ti ratios were predominant during glacials in comparison with interglacials. Specifically, the εNd amplitude through MIS 11–5 differs from that in the remainder of the records, which is also expressed in the magnetic coercivity cycles with subdued patterns. Following source identification on the basis of the detrital Sr–Nd distribution, we recognize two main (rock type) sources and infer two types of ice drainage flow pattern (“flank” and “channelized”), which follow different pathways in the Lambert Glacier–Amery Ice Shelf system (LG-AISS). The first follows an eastern path connecting the Ingrid Christensen Coast (flank), while the second follows a central channel via the LG-AISS (channelized) during MIS 11–5. Regular dynamics on glacial–interglacial timescales, manifested by changes in magnetic coercivity, are closely related to the modeled Antarctic ice volume and ice sheet movement, in which the second channelized pathway during MIS 11–5 corresponds to a 340-kyr-long episode with contiguous warmer-than-present Antarctic interglacials (MIS 11, 9, 7, and 5). Our records thus provide the clearest evidence so far of variable patterns of ice sheet dynamics during the late Pleistocene in the Prydz Bay sector of East Antarctica, which coincided with similar variation of ice drainage during the late Miocene–early Pliocene at around 1.13 Ma (ODP188). Similar ice drainage changes in these two periods imply that major ice flow reconfiguration can be triggered repeatedly by abrupt changes from a stable warm period to a cold one. The presented data not only reveal glacial–interglacial cyclicity in ice sheet advance and retreat in the meridional direction, but also implicate latitudinal adjustment (lateral) within a thin elongated drainage basin of the LG-AISS.
... Boger et al. (2001) interpreted a terrane boundary separating the Lambert and Ruker Provinces as the suture, suggesting their affinity with the Indo-Antarctic and Australo-Antarctic sectors, respectively. However, the Ruker Province was later identified to possess similarities with the basement terranes of Indo-Antarctica (Phillips et al., 2006;Mikhalsky et al., 2010;Flowerdew et al., 2013;Mulder et al., 2019). The uncertainty with respect to the position of the suture not only has implications for the location of India and East Antarctica in Rodinia and Gondwana supercontinent configurations, but also in understanding the interconnected crustal architecture-ice sheet dynamics. ...
... They also interpreted the Ruker-Lambert boundary as a crustal-scale structure, but the age data are not conclusive enough to be assigned either to the Grenvillian or Pan-African time. Mikhalsky et al. (2010) found striking similarities between the Rauer Group and Ruker Complex on the basis of orthogneiss protolith emplacement ages of >3300 Ma and 2850-2800 Ma and similar Sm-Nd T DM model ages. This implies conjugate evolution of the Rauer and Ruker Terranes since 2500 Ma, contradicting the general idea of their separate evolution until 530 Ma (Boger et al., 2001;Zulbati and Harley, 2007). ...
The Rayner Complex of East Antarctica and the Eastern Ghats Province (EGP) of India are thought to have been contiguous in past supercontinents like Rodinia and Gondwana. These terranes have been correlated on the basis of similar granulite facies metamorphic imprints and isotopic age data that testify to Grenvillian (1100-900 Ma) and Pan-African (650-450 Ma) thermal signatures. The Grenvillian granulite facies metamorphic event is generally thought to represent collision between Antarctica and cratonic India, but the precise location of the Indo-Antarctic suture is disputed. The intensity of Pan-African age geological imprints is also variable in both continents, and their significance remains unclear. In this review, we correlate structural, metamorphic and geochronological data in both terranes and parts of their bounding cratons, and suggest that the Ruker Terrane and Rauer Group in Antarctica were continuous with the Rengali Province in India. Together with the established correlation between the EGP and the Rayner Complex, this implies that cratonic India along with the EGP-Rayner amalgam collided with the Archaean Ruker Terrane (part of the Crohn craton) at ∼520 Ma along the southern Prince Charles Mountain in East Antarctica. This suture is distinct from the Grenvillian suture between EGP-Rayner and cratonic India.
... Mount Ruker is a nunatak (from the Inuit word "nunataq"; a mountain/hill that rises above the ice surface) in the Ruker Terrane in the Prince Charles Mountains, East Antarctica (Fig. 1). Despite the remoteness of this area, several authors have investigated the geology of this polyphase Archaean-Palaeoproterozoic basement and provided rather detailed stratigraphic information (e.g., Kamenev et al., 1993;Phillips et al., 2005;Boger et al., 2006;Mikhalsky et al., 2006;Phillips et al., 2006;Mikhalsky et al., 2010;Liu et al., 2017;Harley et al., 2013 and references therein). Hence, we here focus on a brief description of the Tingey Complex which hosts the Ruker Group and Mt. ...
... However, the Ruker Group, including the Mt. Ruker BIF, underwent metamorphism only up to greenschist facies (Mikhalsky et al., 2010), favouring preservation of an original major and trace elemental composition of the Mt. Ruker BIF. ...
Here we report the first detailed geochemical data for Banded Iron-Formation (BIF) from Antarctica. Micro drill cores were taken from adjacent magnetite/haematite and metachert bands from the 2.5 Ga old Mt. Ruker BIF, Prince Charles Mountains, East Antarctica. Low concentrations of Al, Zr, Hf, and Sc reveal the purity of the samples. The chemical composition matches closely that of other early Precambrian BIF, except for an enrichment of Ni, and high Ba/Sr ratios in the metachert. Shale-normalized Rare Earths and Yttrium (REYSN) patterns show all the features of modern seawater such as depletion of light vs heavy REY, positive anomalies of LaSN, EuSN, GdSN, and YSN (i.e. super-chondritic Y/Ho ratios) and the W-type lanthanide tetrad effect (LTE), but no CeSN anomalies (and no positive Eu anomalies in chondrite-normalized REY patterns). This distribution is fully compatible with that of other pure Early Precambrian BIFs, suggesting high-temperature hydrothermal input of REY into seawater and a redox level of the atmosphere-hydrosphere system too reducing for Ce oxidation. The uniform, super-chondritic Y/Ho ratios in adjacent iron-oxide and metachert BIF bands most strongly suggest that the conspicuous banding does not result from post-depositional separation of an initially homogenous Fe-silicate precipitate, but argues for a primary origin of the banding. The super-chondritic Y/Ho ratios fit well within the range reported for other BIF worldwide, corroborating that positive Y anomalies, although possibly of smaller size than today, have always been a characteristic feature of seawater. The Mt. Ruker BIF further complements the set of Early Precambrian marine chemical sediments in which the W-type LTE has been observed, and demonstrates the antiquity of the LTE in seawater. These subtle features reveal that the distribution of the redox-insensitive REY in seawater did not change significantly over the almost 4 billion years geological record of seawater. The super-chondritic Y/Ho ratios and W-type LTE in this and other oxide-facies BIF are in marked contrast to the REY distribution in Modern and Cenozoic oxidic hydrogenetic ferromanganese crusts, pointing towards fundamentally different removal mechanisms of REY from Modern vs Early Precambrian seawater.
... Исследованный район расположен в пределах раннедокембрийской Рукерской тектонической провинции (рис. 1, А), в строении которой выделяются архейско-среднепалеопротерозойская гранито-гнейсовая инфраструктура и палеопротерозойско-неопротерозойская парагнейсово-сланцевая супраструктура. Инфраструктура была сформирована на временных интервалах 3400-2700 и 2500-2100 млн лет назад (Boger et al., 2006;Mikhalsky et al., 2010) и сложена разнообразными орто-и парагнейсами. Супраструктура включает три в различной степени метаморфизованных осадочных комплекса, максимальный возраст накопления которых составляет 2500 млн лет (серия Рукер), 1800 млн лет (серия Мензис) и 1000 млн лет (серия Содружества) (по данным U-Pb датирования детритового циркона, Phillips et al., 2006). ...
... Для пород серии Рукер оценок Р-Т условий метаморфизма ранее получено не было. Особенности геологического развития и вещественный состав гранитогнейсовой инфраструктуры изучены достаточно подробно (Mikhalsky et al., 2010, и ссылки в этой работе), тогда как комплексы супраструктуры -только на рекогносцировочном уровне (Равич и др., 1978). Без реконструкции вещественного состава субстрата и характера метаморфизма этих толщ невозможно дальнейшее развитие представлений о тектонической эволюции как данного региона, так и всей Восточно-Антарктической платформы. ...
В горах Принс-Чарльз вскрыты разнообразные геологические комплексы, формирующие кристаллический фундамент Восточно-Антарктической платформы. Серия Рукер входит в число метаосадочных комплексов, слагающих палеопротерозойско-неопротерозойскую супраструкту-
ру Рукерской тектонической провинции. Она делится на две толщи, включающие метаосадочные и метавулканические породы, интенсивно дислоцированные и метаморфизованные в условиях фации зеленых сланцев. С целью реконструкции Р—Т параметров метаморфизма изучен вещественный состав представительных образцов метавулканических пород и выполнено физико-химическое моделирование минеральных парагенезисов. Проанализирована зависимость
минерального состава метабазитовых сланцев от состава протолита и соотношения компонентов водно-углекислотного флюида, участвующего в фазовых реакциях. Рассчитана мольная доля CO2 во флюиде, равновесном с карбонатсодержащими парагенезисами (0.13—0.27). Показано, что хлоритоидные сланцы образовались в результате метаморфизма апобазальтовых латеритов.
Результаты моделирования и данные хлорит-фенгитовой термобарометрии указывают на условия метаморфизма пород серии Рукер, соответствующие высокобарической части зеленосланцевой фации (температура 300—450 °C, давление до 7—8 кбар). Эти условия значительно пре-
вышают геотерму стабильной континентальной коры и близки к условиям эндогенного режима в зонах «медленной» субдукции океанической коры. По имеющимся геологическим данным подобная геодинамическая обстановка могла сложиться в ходе эволюции неопротерозойского
осадочного бассейна внутриплитного заложения в связи с погружением фрагментов фундамента на большие глубины как результат тектонического скучивания при закрытии бассейна.
... Для ортогнейсовых пород Ламбертской области получены следующие датировки: 3520, 2600, 2100-1800, 1600 (Boger et al., 2001;Boger et al., 2008;Corvino, Henjes-Kunst, 2007); 2250-2150 млн лет (кристаллизация габбро), около 2060-2000 и 1800 млн лет (внедрение фельзических жил, связанных с частичным плавлением и метаморфизмом гранулитовой фации, Mikhalsky et al., 2010). Внедрение жил, даек и мелких штокообразных тел перглиноземистых лейкогранитов датировано возрастом 500±5 млн лет. ...
... Результаты анализа АМП свидетельствуют, что в зоне Моусона доминируют короткопериодные аномалии (10-20 км), и она соответствует внешней и в значительной степени переработанной части кратона, где преобладают породы Ламбертской сланцево-гнейсовой области , возможно, сохранившей в ряде мест (например, на уступе Моусона) компоненты Рукерской гранит-зеленокаменной области (Boger et al., 2001;Mikhalsky et al., 2001), но вместе с тем испытавшей значительную тектонотермальную активизацию в ранненеопротерозойское (~940-880 млн лет) и кембрийское (530-490 млн лет) время (Corvino et al., 2008;Phillips et al., 2009;Mikhalsky et al., 2010). ...
PCMEGA совместно с информацией российских исследователей для южной части гор Принс-Чарльз дает воз-можность установить границу между Рукерской архейской гранит-зеленокаменной облас-тью и областью мезонеопротерозойского тектогенеза. Подразделение магнитной области Рукер на три зоны, в которых присутствуют элементы упорядоченности и заметная конт-растная зональность в распределении аномалий вокруг центрального ядра, свидетельству-ет о том, что большая часть этой территории подстилается глубоко метаморфизованным гранитогнейсовым фундаментом, главные тектономагматические события в пределах ко-торого происходили в раннем докембрии в интервале времени 3500—2100 млн лет назад. Появление положительных аномалий служит основным критерием для выделения облас-тей развития интрузивных пород фундамента, тогда как малые гранитоидные тела (дайки, жилы), многократно внедрившиеся в интервале времени между 2750 млн лет и 2200 млн лет в различных тектонических условиях, не могут выступать в роли основных источников закартированных аэромагнитных аномалий локально-регионального развития по причине их малых размеров. Наблюдаемый структурно-морфологический рисунок распределения аномалий магнит-ного поля может свидетельствовать о незначительной протяженности древних терригенных бассейнов по причине отсутствия протяженных участков спокойного и/или отрицательно-го поля, коррелируемых с известными обнажениями супракрустальных толщ. Тем не менее, территория, отвечающая зоне Коллинса, может быть рассмотрена в качестве наиболее об-ширной площади, сложенной метаморфическими породами супракрустального происхож-дения серии Ламберта, формировавшихся в мезопротерозойское время, тогда как аномалия Рукер, отвечая категории структур рифтогенно-трогового происхождения, позволяет уве-ренно картировать область распространения пород осадочного комплекса. Моделирование источников аномалии Рукер показывает, что наблюдаемые аномалии могут быть подобраны сложным по форме близповерхностным телом, мощность которо-го не превышает 1,2—2 км. Выполненный подбор источников для региональной аномалии Меллора свидетельствует о том, что ее основным источником также могут быть породы джеспилитовой формации, погруженные на глубину порядка 2 км. Как альтернативный ва-риант в качестве ее источника можно рассматривать мощную интрузию основного/ультра-основного состава, по своим размерам сопоставимой с крупнейшими интрузиями Мира.
... Ga (Fitzsimons, 2003). Farther west, in the P1b region, 495-550 Ma felsic magmatic and high-grade metamorphic rocks have reworked ca 1020-1400 Ma mafic and felsic protoliths (Rayner Complex) in Prydz Bay and the Grove Mountains (Liu, Zhao, & Hu, 2013), and a mixture of Archean (Ruker Complex) and Paleoproterozoic (Lambert Complex) protoliths, with local Grenvillian reworking (900-990 Ma Rayner Event), in the southern Prince Charles Mountains (Mikhalsky, Henjes-Kunst, Belyatsky, Roland, & Sergeev, 2010). Panafrican granitoids in the southern Prince Charles Mountains have e Nd (t) values of -28 to -10 (mostly -23 to -18), Figure 31. ...
... Numbers are keyed in Tables 3-6. consistent with reworking of local 2800-3400 Ma basement rocks (model ages mostly 2.4-3.6 Ga; Mikhalsky et al., 2010), while those in the Grove Mountains have zircon e Hf values (estimated from Nd data) of -13.4 to -9.2 and model ages of 1.6 to 2.1 Ga (Liu et al., 2006), consistent with reworking of the Grenvillian Beaver Terrane and related rocks of the Rayner Complex. ...
Lower to upper Middle Ordovician quartz-rich turbidites form the bedrock of the Lachlan Orogen in the southern Tasmanides of eastern Australia and occupy a present-day deformed volume of ∼2–3 million km³. We have used U–Pb and Hf-isotope analyses of detrital zircons in biostratigraphically constrained turbiditic sandstones from three separate terranes of the Lachlan Orogen to investigate possible source regions and to compare similarities and differences in zircon populations. Comparison with shallow-water Lower Ordovician sandstones deposited on the subsiding margin of the Gondwana craton suggests different source regions, with Grenvillian zircons in shelf sandstones derived from the Musgrave Province in central Australia, and Panafrican sources in shelf sandstones possibly locally derived. All Ordovician turbiditic sandstone samples in the Lachlan Orogen are dominated by ca 490–620 Ma (late Panafrican) and ca 950–1120 Ma (late Grenvillian) zircons that are sourced mainly from East Antarctica. Subtle differences between samples point to different sources. In particular, the age consistency of late Panafrican zircon data from the most inboard of our terranes (Castlemaine Group, Bendigo Terrane) suggests they may have emanated directly from late Grenvillian East Antarctic belts, such as in Dronning Maud Land and subglacial extensions that were reworked in the late Panafrican. Changes in zircon data in the more outboard Hermidale and Albury-Bega terranes are more consistent with derivation from the youngest of four sedimentary sequences of the Ross Orogen of Antarctica (Cambrian–Ordovician upper Byrd Group, Liv Group and correlatives referred to here as sequence 4) and/or from the same mixture of sources that supplied that sequence. These sources include uncommon ca 650 Ma rift volcanics, late Panafrican Ross arc volcanics, now largely eroded, and some <545 Ma Granite Harbour Intrusives, representing the roots of the Ross Orogen continental-margin arc. Unlike farther north, Granite Harbour Intrusives between the Queen Maud and Pensacola mountains of the southern Ross Orogen contain late Grenvillian zircon xenocrysts (derived from underlying relatively juvenile basement), as well as late Panafrican magmatic zircons, and are thus able to supply sequence 4 and the Lachlan Ordovician turbidites with both these populations. Other zircons and detrital muscovites in the Lachlan Ordovician turbidites were derived from relatively juvenile inland Antarctic sources external to the orogen (e.g. Dronning Maud Land, Sør Rondane and a possible extension of the Pinjarra Orogen) either directly or recycled through older sedimentary sequences 2 (Beardmore and Skelton groups) and 3 (e.g. Hannah Ridge Formation) in the Ross Orogen. Shallow-water, forearc basin sequence 4 sediments (or their sources) fed turbidity currents into outboard, deeper-water parts of the forearc basin and led to deposition of the Ordovician turbidites ∼2500–3400 km to the north in backarc-basin settings of the Lachlan Orogen.
... The Rucker Complex localized in the uppermost reaches of the Lambert Glacier (the Prince Charles Mountains to the south of Mount Cresswell, the Solov'ev and Commonwealth mountains) and in the southern one third of the Mawson Escarpment is characterized by its inhomogeneous structure and complex geological history [3,17,18,58,60,73]. The overwhelming majority of its outcrops are cut by swarms of basic dikes and sills, the youngest of which are practically undeformed and only affected by greenstone facies alteration. ...
... Some of them contain relict hypersthene. The available data show that granitic rocks were emplaced and crystallized 3400-3000 Ma ago [32,57,58]. The model Nd ages of 3900-3200 Ma [59] assume that even older Archean rocks may exist. ...
The information on the composition, structure, P-T conditions of metamorphic facies, evolution, and time of the metamorphic events in the largest Precambrian tectonic provinces of the Antarctic Crystalline Shield gained over more than a half-century is summarized in this paper. The joining up of the ortho- and paracrystalline rocks into complexes and groups according to their geographic position, composition, age, and the character of their metamorphism allowed us to consider the main features of the structure and evolution of the provinces including (1) the near-latitudinal polycyclic Late Precambrian-Early Paleozoic Wegener-Mawson Mobile Belt, extended for more than 4000 km, which started to evolve in the Mesoproterozoic and stabilized only at the end of Cambrian; (2) the Early Precambrian relict crystalline protocratonic blocks adjoining this mobile belt; their history is traced from the Eoarchean; and (3) the near-latitudinal Late Precambrian-Early Paleozoic aulacogen in the southern protocratonic block. The P-T conditions of the metamorphism from the pyroxene-granulite subfacies in the protocratonic blocks to the greenschist facies in aulacogen, as well as the age of the magmatic and metamorphic events in all the tectonic provinces of the shield, are characterized. This made it possible to consider the metamorphic history and conditions of the continental crust’s formation in Antarctica, where the oldest crystalline rocks are dated to the Eoarchean (4060–3850 Ma) and the youngest rocks are ∼500 Ma old.
... According to Mikhalsky et al. (2010), the Rauer-Ruker correlation in East Antarctica is evident from the similar orthogneiss protolith emplacement ages of >3300 Ma and 2500-2800 Ma along with similar Sm-Nd model ages. This supports the contiguous evolution of the Rauer Group and the Ruker Terrane as a single crustal unit since 2500 Ma. ...
... The Grenvillian orogens are subdivided into the older (1300-1050 Ma) and younger (1050-900 Ma) ones. The former is distributed across southern Laurentia, western Australia, western East Antarctica, and Kalahari (Goodge et al., 2017;Fitzsimons, 2003;Kirkland et al., 2011;Möller et al., 2002;Milidragovic et al., 2011), and the latter occurs in northern East Antarctica (Mikhalsky et al., 2010(Mikhalsky et al., , 2013 and eastern India (Chattopadhyay et al., 2015;Dasgupta et al., 2013). The G4 sedimentary rocks in the KTM have striking detrital-zircon age peaks at 1740 Ma and 1348 Ma with a minor peak at 1116 Ma. ...
The Kontum Massif (KTM) is the largest Precambrian basement exposure in the Indochina Block, Southeast Asia. The compositions and formation ages of the KTM basement rocks and the paleo-position of the KTM in Proterozoic supercontinents have not been well constrained. Zircon U-Pb-Hf isotopic data of sixteen samples from the KTM in this study indicate that the KTM basement consists mainly of different units of metasedimentary rocks. These sedimentary rocks were deposited in five periods, late Paleoproterozoic (G1, 1.80–1.65 Ga), late Paleoproterozoic - early Mesoproterozoic (G2, 1.74–1.45 Ga), Mesoproterozoic (G3, 1.4–1.1 Ga), late Mesoproterozoic - early Neoproterozoic (G4, 1.1–0.81 Ga), and late Neoproterozoic - early Paleozoic (G5, 0.61–0.51 Ga), and underwent three phases of metamorphism in the early Paleozoic (501–415 Ma), late Paleozoic (371–331 Ma), and Indosinian (272–235 Ma). The G1 and G2 sedimentary rocks have abundant Neoarchean (2.63–2.48 Ga) and late Paleoproterozoic (1.83–1.74 Ga) detritus, and the G3 and G4 sedimentary rocks consist mainly of late Paleoproterozoic (1.74–1.72 Ga) and middle Mesoproterozoic (1.41–1.35 Ga) clastic materials. The G5 sedimentary rocks are characterized by consecutive Mesoproterozoic detrital zircon age spectra with a wide age peak at 1.06–1.01 Ga, much different from the G1 to G4 sedimentary rocks. Most Archean detrital zircons show juvenile Hf isotopes, whereas late Paleoproterozoic, middle Mesoproterozoic, and Grenvillian zircons show large Hf-isotope variations. Most detrital zircons are exotic because coeval igneous rocks have not been identified in the KTM (or elsewhere in Indochina), except ∼1.44 Ga ones.
Comprehensive comparisons of detrital zircon U-Pb, Hf isotopes and sedimentary environments of these five units of sedimentary rocks with the extensive magmatism and coeval siliciclastic rocks in different cratons and microcontinents suggest that most of the Precambrian sediments in the KTM were derived from southwestern Laurentia, and the KTM has maintained a long-time connection with southwestern Laurentia for about one billion years from the G1 to the G4. The KTM was adjacent to Hainan Island and Tasmania during the G3-G4 deposition. The U-Pb ages and Hf isotopes of detrital zircons and sedimentary environment of the G5 sedimentary rocks indicate that the KTM was located on the northern margin of East Gondwana and near South China, India and western Australia, consistent with previous configurations for the Indochina Block. Therefore, the KTM, together with South China and Hainan Island, experienced quick northward movement from southwestern Laurentia to the northern margin of East Gondwana during the G4 (ca 1.10–0.81 Ga) to the G5 (0.61–0.51 Ga), which is also supported by new paleomagnetic data.
... According to the data of [58], they characterize volcanic covers of metamorphic rocks attributed to greenstone belts that developed within Antarctica. About 130 Ma ago, trap magmatism associated with the action of the Kerguelen Plume on the eastern margin of Antarctica was manifested in this area [22]. ...
A zircon with an age of ~2.9 Ga, much older than all existing dates, has been discovered for the first time in basalts of the Afanasy Nikitin Rise. Such an ancient age is typical of continental crust rocks of Western Hindustan or Antarctica. Analyses have revealed the geochemical similarity of magmas of the Conrad and Afanasy Nikitin rises and their difference from Crozet Rise magmas owing to their different formation conditions. Emplacement of the Conrad and Afanasy Nikitin rises occurred ~80–90 Ma ago under the influence of the same Conrad hotspot near the spreading Indian–Antarctic Ridge. This hotspot is a satellite of the giant Kerguelen Plume, active in the Eastern Indian Ocean from 130 Ma ago to the present. The plume formed the Ninetyeast Ridge in the ancient spreading center, and plume magmas leaked along the spreading zone up to the formation area of the Conrad and Afanasy Nikitin rises. During interaction of the Kerguelen Plume with the spreading zone and transform faults, nonspreading blocks of the ancient continental lithosphere of the Gondwana may have been preserved.
... The 3470-3260 Ma magmatism, 2840-2800 Ma metamorphism and partial melting accompanying magma intrusion, and 2550 Ma igneous activity recorded by felsic orthogneisses in the Archean crustal domain correspond with tectonothermal events recorded by felsic orthogneisses in the Ruker Terrane of southern Prince Charles Mountains (Boger et al., 2006;Mikhalsky et al., 2006;Mikhalsky et al., 2010). The Pb isotopic compositions of feldspar also suggest that the two basement terranes share an early crustal history (Flowerdew et al., 2013). ...
A U–Pb geochronological and rare earth element (REE) geochemical study of zircon, monazite and garnet was carried out on rocks of Mesoproterozoic and Archean crustal domains in the Rauer Group of East Antarctica. The zircon and monazite U–Pb age spectra define concordia intercepts mainly at ca 1200, 990–910, and 530–500 Ma, suggesting that the Mesoproterozoic crustal domain is a significant part of the Rayner Complex that also underwent early Neoproterozoic and Cambrian high-grade metamorphism. The age data, mineral inclusion assemblages in zircon, and REE features for zircon and garnet indicate that all the granulite facies mineral assemblages in this domain might have formed during early Neoproterozoic metamorphism. Some zircon and monazite grains or domains have experienced complete U–Pb isotopic resetting during Cambrian reworking, which did not result in new zircon and monazite growth. The Archean crustal domain consists mainly of Paleo–Mesoarchean orthogneisses interleaving with Neoproterozoic paragneisses that contain inherited metamorphic zircon domains with ages of ca 1330 and 970 Ma. The mineral assemblages in these gneisses formed during a single Cambrian granulite facies metamorphic event. Garnet-bearing and -free rocks cooled to solidus temperatures at ca 527 and 517 Ma, respectively, whereas the isotopic system of early-crystallized zircon was completely reset during the growth of new zircon. As such, all the zircon domains in the same sample could have the same concordant or weighted mean age. The 511 Ma monazite and 506 Ma zircon overgrowths in a paragneiss have REE contents in equilibrium with garnet, implying that later modification and isotopic resetting of zircon and monazite might have resulted in younger U–Th–Pb ages and, in this case, establishing the age–mineral assemblage relationship based on REE partition coefficients between zircon/monazite and garnet may be invalid. Overall, the available data support the notion that different crustal components of the Rauer Group were juxtaposed in the Cambrian as a consequence of the Gondwana assembly.
... The studied region belongs to the Early Precambrian Ruker Terrane (Fig. 1a), within which the Archean to Middle Paleoproterozoic granite-gneiss infrastructure and Paleoproterozoic to Neoproterozoic paragneissic schist suprastructure are identified. The infrastructure was formed over the range of 3400-2700 to 2500-2100 Ma (Boger et al., 2006;Mikhalsky et al., 2010) and is composed of diverse ortho-and paragneisses. The suprastructure consists of three variable metamorphosed sedimentary complexes with the maximum sedimentation ages of 2500 Ma (Ruker Group), 1800 Ma (Menzies Group), and 1000 Ma (Sodruzhestvo Group) (on the basis of U-Pb detrital zircon geochronology, Phillips et al., 2006). ...
Zapiski RMO (Proceedings of The Russian Mineralogical Society). 2019. Vol. 148. N 5. P. 24-44. DOI: 10.30695/zrmo/2019.1485.01 (in Russian with English abstract). English translation: Geology of Ore Deposits. 2020. V. 62. N 7. P. 584-598. DOI: 10.1134/S1075701521070047 # Diverse geological complexes that form the crystalline basement of the East Antarctic Platform crop out in the Prince Charles Mountains. The Ruker Group is a member of the metasedimentary complexes
that make up the Paleoproterozoic through Neoproterozoic suprastructure of the Ruker Terrane. It is divided into two sequences consisting of highly deformed and greenschist facies metamorphosed sedimentary and volcanic rocks. The mineral and major element compositions of metavolcanic rocks have been studied and physicochemical modeling of mineral parageneses has been performed to reconstruct the P–T parameters of
metamorphism. The dependence of the mineralogy of metabasic schists on the protolith composition and the ratio of components in the H2O–CO2 fluid involved in the phase reactions were analyzed. The calculated mole fraction of CO2 in the fluid equilibrated with carbonate-bearing parageneses is 0.13–0.27. It is assumed
that chloritoid schist consists of metamorphosed laterites derived from basalt. Modeling and the data of chlorite–phengite thermobarometry indicate that the Ruker Group rocks were metamorphosed under conditions of the high-pressure part of the greenschist facies (300–450°C, 7–8 kb). These conditions are significantly higher than the stable continental geotherm and are close to those in the zone of a slow subduction geotherm.
According to the available geological data, a similar geodynamic setting could be caused by the evolution of the Neoproterozoic intraplate sedimentary basin in connection with deep-sinking basement blocks as a result of tectonic aggregation during the closure of the basin
... The Lambert terrane (to the north of Harbour Bluff) in the southern Prince Charles Mountains (sPCM) ( Figure 5) is a Paleoproterozoic basement (Mikhalsky et al., 2010(Mikhalsky et al., , 2006Corvino et al., 2008), which was reworked during the Pan-African event at upper amphibolite-facies metamorphism (peak P-T conditions of 630-700º C, 0.6-0.7 GPa, Phillips et al., 2009, Boger andWilson, 2005). The event was also manifested with localized shear zone development and/or reactivation and the sporadic emplacement of pegmatite and granitic sheets (Corvino et al., 2011(Corvino et al., , 2008Mikhalsky et al., 2006). ...
The Pan‐African event is widely distributed in East Antarctica craton. Many terranes or outcrops of the craton bear more or less signs of the event. From characteristics of the shear zones, granites, pegmatites, feature and time of high grade metamorphism and detrital zircon ages peaks of the downflowing sediments from the plateau, the Pan‐African event in the East Antarctica and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, wasdistributed as special zones or areas in many localities, including both the coastal regions and interior of the East Antarctica. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bi‐modal feature. The water or fluid available along the shear zones were responsible for retrogression of the earlier, e.g., Grenville age, high grade outcrops to later Pan‐African amphibolite facies metamorphism. Meanwhile, the Pan‐African event has influenced most isotopic systems, including the U‐Pb, Sm‐Nd, Rb‐Sr and Ar‐Ar systems, giving younger apparent ages. Manifestation of the Pan‐African event is distributed from possibly locally granitic magmatism, to wider medium‐high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect. Before Gondwana formation, local depressions in the East Antarctica could be filled with sediments, implying the initial breakup period of the Rodinia. The later Pan‐Gondwana counterrotating cogs shaped the interstitial fold belts between continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the widespread granites, pegmatites and more or less isotopic resetting due to strong thermal effect from the deep. That is, the Pan‐African event is a possible response of the plate movement surrounding the continent swarms in the non‐stable interior of theyet consolidated Gondwana. The Pan‐African event may be an overwhelmingly extensional and transcurrent tectonics in mechanism.
... This is interpreted as the age of amphibolite metamorphism in the Mount Creswell region, indicating that these rocks are part of the Beaver terrane. Our preliminary data suggest that the Ruker, Lambert and Beaver terranes amalgamated before peak metamorphism at 1000-900 Ma in the Beaver terrane, challenging the widely held view that there is a Cambrian suture in the Prince Charles Mountains and consistent with arguments that the Prince Charles Mountains might have assembled at ~1.0 Ga (Phillips et al., 2009;Mikhalsky et al., 2010). ...
Granulite terranes of the Indian peninsula have served as an important proxy in reconstruction
of supercontinent assemblies. The South Delhi terrane has been extended into the East
African orogen and Southern Granulite terrane has been correlated with Madagascar in East
Gondwana assembly. Here we highlight the compression and extension tectonics that were
important in the evolution of the Indian granulites, and which could provide important criteria
for reconstructions.
Granulites occur as an exhumed terrain surrounded by low-grade rocks of the South Delhi
terrane in the Delhi–Aravalli mobile belt of NW India. The contact is marked by marginal
faults, cataclasites and pseudotachylites. In the early stage of evolution, pelitic granulite, calc
granulite, basic granulite and several phases of Ambaji granites underwent compressional
tectonics marked by multiple stages of buckle folds. The peak granulite facies metamorphism
was syn-tectonic with F1 folding; F2 folding which is coaxial with F1 was accompanied by
syn- to post-kinematic brittle–ductile thrusting. Mylonites show a quartz-ductile–feldsparbrittle
condition, suggesting shearing P-T conditions of 15 km and 500–550oC. Hence it has
been argued that the granulites were exhumed by thrusting from such great depth to as little
as 5 km, where brittle deformation led to formation of pseudotachylites and cataclasites. F3
folds produced domal outcrops and caused plunge reversal of the earlier folds. In late stage
deformation, extensional faults were developed with associated normal slip, block rotation and
roll-over structures. The extension led to crustal thinning so that the granulites were exposed
in due course through erosion. SHRIMP U-Pb zircon dating yielded ages of 1200–900 Ma for
sedimentation, 860 Ma for F1 folding-granulite facies metamorphism, 800 Ma for F2 folding
and thrusting and 750 Ma for late stage granite emplacement. Monazite dating of the granulite
and mylonites show the extensional faults to be 699–647 Ma. Thus the South Delhi terrane
belongs to the Neoproterozoic era, between Rodinia break-up and Gondwana assembly.
Part of the Southern Granulite terrane lying between the Salem–Attur and Palghat Cauvery
shear zones here named the Salem–Namakkal subterrane is Paleoproterozoic. Mafic granulites,
charnockites, granite gneisses, granites and BIF are the main rock types, which show coaxial
folding (F1 and F2) in a compressional setting. SHRIMP dating shows the peak granulite
facies metamorphism to be 2.5 Ga old. However, the granulites were retrograded during lowangle
thrusting towards the NNE, which exhumed the rocks to the upper crust. Cataclasites
and pseudotachylites were produced subsequently. Based on EPMA dating of monazite, the
thrusting is constrained to between 1140±27 Ma and 814.3±16 Ma. Late stage extension gave
rise to extensional faults, block rotation, detachment and roll-over structures. Hence thrusting
and extension is interpreted to be syn-tectonic with that in the South Delhi terrane. Thus both
granulite terranes underwent compression and extension tectonics in their evolution, with
exhumation between Rodinia and Gondwanaland orogenies.
... The source of the c. 1796 Ma zircon core is problematic as we found no comparable felsic magmatic rock in the Prydz Bay area. However, the Fisher Terrane and Beaver Terrane of the Prydz Bay area show detrital zircon signatures of c. 2800-2500 Ma, 2200-2100 Ma and 1900-1700 Ma (Mikhalsky et al., 2010). It is possible that the detritus of the latter age group was also received in the Chilka lake area. ...
Orthopyroxene-bearing felsic gneiss occurs as foliation-parallel layers and bands together with aluminous granulite, mafic granulite, and quartzofeldspathic granulite in the Chilka Lake migmatite complex of the Proterozoic Eastern Ghats Belt, India. The rock was classified previously as charnockite which underwent granulite-facies metamorphism. Field and textural features of this rock show evidence of the partial melting of a biotite-bearing greywacke protolith. Orthopyroxene with/without garnet and cordierite were produced with K-feldspar as peritectic phases of incongruent melting of presumed metaluminous sediments. Fluid-inclusion data suggest the presence of high-density CO 2 -rich fluids during peak metamorphism, which are similar to those found in associated aluminous granulite. Whole-rock major and trace element data show wide variability of the source materials whereas REE distributions show enriched LREE and flat HREE patterns. Zircon grains from representative samples show the presence of inherited cores having spot dates (SHRIMP) in the range c. 1790–3270 Ma. The overgrowth on zircon was formed predominantly during c. 780–730 Ma and sporadically during c. 550–520 Ma. Some neoblastic zircons with c. 780–730 Ma ages are also present. U-rich dark zones surrounding cores appear partially metamictised, but spot ages from this zone vary within c. 1000–900 Ma. The <1000 Ma ages represent metamorphism that mirrors the events in associated aluminous granulite. The sources of metaluminous sediments are speculative as the rock compositions are largely modified under granulite-facies metamorphism and partial melting. Considering the accretionary tectonic setting of the Eastern Ghats Belt during the c. 1000–900 Ma time frame, a greywacke-type protolith for the migmatite complex has been proposed.
... Рукерская гранит-зеленокаменная область располагается в южной части ГПЧ (рис. 1а), занимая площадь к западу от ледника Ламберта и южную оконечность уступа Моусон, сложенного одноимённой ортогнейсовой серией, для которой ранее были получены наиболее древние архейские возраста до 3400 млн лет [3]. Ортогнейсы серии Моусон рас-сматривались как фундамент для серий Мензис, Рукер и Содружество мезоархейского, палео-и неопротерозойского возраста соответственно. ...
Paper presents results of isotope studies of primary igneous and sedimentary rocks of Mawson and Menzies series from the southern Prince Charles Mountains, East Antarctica. Obtained data show that igneous protholith crystallization of Mawson orthogneiss occurred at 3164,2±9,2-3163,2±7,8 Ma ago. The Mawson orthogneiss were a basement for Menzies series sediment. The maximum time of sediment deposition is estimated to be in the range of 3,0-3,1 Ga. Sediment protholith involves an admixture of Paleoarchean material.
... The Ruker granite-geenstone province of southern PCM (Fig. 1a) occupies the area west to Lambert Glacier and southern part of Mawson Escarpment composed of the Mawson Orthogneiss which yielded most oldest Archaean ages up to 3400 Ma [3]. Orthogneisses of the Mawson series were considered as the basement for the emplacement of Menzies, Ruker, and Commonwealth series of the Mesoarchean, Paleoarcean, and Neoproterozoic age. ...
This work presents results of isotope studies of primary igneous and sedimentary rocks of Mawson and Menzies series from the southern Prince Charles Mountains, East Antarctica. The data obtained show that the crystallization of the protolith of Mawson orthogneisses occurred at 3164.2 ± 9.2-3163.2 ± 7.8 Ma ago. The Mawson orthogneisses were the basement for accumulation of the deposits of the Menzies series. The maximum time of the deposition is estimated to be in a range of 3.0-3.1 Ga. The protolith of Menzies sedimentary deposits contains an admixture of the Paleoarchean material.
... Instead, the Ruker Province has a Pb-isotopic composition similar to basement terranes in Indo-Antarctica ( Fig. 2A; Flowerdew et al., 2013a). We suggest that the Ruker Province forms part of Indo-Antarctica (see also, Phillips et al., 2006;Mikhalsky et al., 2010) and that the terrane boundary exposed in the southern Prince Charles Mountains does not represent a suture between Australo-Antarctica and Indo-Antarctica. Therefore, any westerly continuation of the Mirny fault into the Prydz Bay region should be located south of the southern Prince Charles Mountains, beneath the polar ice cap ( Fig. 1B; Fitzsimons, 2003). ...
East Gondwana is generally thought to have assembled through the amalgamation of Indo-Antarctica and Australo-Antarctica along the Ediacaran–Cambrian Kuunga orogen. The location of a boundary between Indo-Antarctica and Australo-Antarctica within this key Gondwana-forming orogen remains controversial because extensive ice cover in East Antarctica precludes traditional characterization of terranes. Here, we integrated Pb-isotope analysis of detrital feldspar grains with U-Pb dating of detrital monazite and zircon grains from offshore sediments to infer the location of the onshore boundary between Indo-Antarctica and Australo-Antarctica. New and compiled data from onshore basement exposures highlight the different age and Pb-isotope signatures of Indo-Antarctica and Australo-Antarctica. Holocene sediments offshore from Mirny Station (Queen Mary Land, East Antarctica) have detrital feldspar Pb-isotope signatures and detrital monazite and zircon U-Pb ages that reflect contributions from both Indo-Antarctica and Australo-Antarctica. The presence of both Indo-Antarctic and Australo-Antarctic crust beneath ice cover near Mirny Station implies proximity to a fundamental terrane boundary within the Kuunga orogen, which could coincide with a geophysical lineament at ~94°E (Mirny fault). The geophysical expression of this boundary extends into the subglacial interior of East Antarctica, where, prior to more recent rifting, it may have connected with one or more previously inferred Gondwana-forming sutures. The revised geometry of the Kuunga orogen suggests that the assembly of East Gondwana involved dominantly strike-slip motion in the Mirny region coupled with high-angle convergence between Indo-Antarctica and Australo-Antarctica to the west.
... Domeier and Torsvik, 2014). The Australian (Johnson et al., 2011b), Antarctic (Mikhalsky et al., 2010) and Indian (Mohanty, 2013) blocks also record magmatic and tectonothermal events during the Early and Middle Paleoproterozoic that where broadly contemporaonues with those recorded among blocks in the "proper" Atlantica assemblages, and would at least be consistent with a proximal position between 2.5-1.8 Ga. ...
The evolution of orogenic systems is a function of their overall tectonic context, and global reconstructions therefore provide a crucial framework for understanding the geodynamic setting of ancient orogens. However, the reverse is also true, as a detailed geodynamic model for an orogenic system can provide valuable insights into its overall tectonic context. Based on a recently proposed geodynamic model for the ca. 2.27-1.96 Ga accretionary-collisional Birimian Orogen in the West African Craton, this study aims to explore its broader tectonic setting, by placing the events outlined on an orogen-scale within a global context. The proposed geodynamic model argues that the Birimian Orogen formed in a plate tectonic setting similar to that which currently characterizes SE Asia, with the orogenic system forming in a wedge-shaped complex plate boundary zone, bordered to the north and south by continental blocks and opening up to face a major oceanic basin. The Neoproterozoic-Paleozoic East African-Antarctic orogen (EAAO) has also been constrained to have formed in such a setting and exhibits significant similarities with the Birimian Orogen with respect to its orogenic evolution. Furthermore, the EAAO and the Birimian Orogen have the same temporal relationship to major environmental perturbations and isotopic excursions in the Neo- and Paleoproterozoic Eras, respectively, which are generally considered to be controlled by global tectonics. Building on previous work, it is argued that this a reflection of how the Paleo- and Neoproterozoic were characterized by an equivalent supercontinent cycle, where the Birimian Orogen assumed an equivalent position to the EAAO. This further requires that the Birimian Orogen formed during the assembly of a Paleoproterozoic equivalent of Gondwana. This is in line with the previous recognition of a ca. 2.1-2.0 Ga continent that included the Birimian Orogen, and which has been referred to as Atlantica. A revised configuration is presented for this continent, which includes crustal domains now present in Africa, South America, Eastern Europe and North China. Gondwana formed during the 1.0 Ga breakup of Rodinia and 0.3 Ga assembly of Pangea, and this cycle forms the basis for a global tectonic reconstruction for the Paleo- and Mesoproterozoic, which places the evolution of the Birimian Orogen within the context of the assembly of Atlantica and global-scale supercontinent cycles. As they are proposed to have formed in an equivalent tectonic setting, the EAAO and the Birimian Orogen also provide an opportunity to study the effect of secular changes during the Proterozoic. Furthermore, since the Birimian Orogen has been noted to have many similarities with Archean orogenic systems, this may indicate that the latter formed in similar complex plate boundary zones, such as currently exist in SE Asia.
... Rickers et al. (2001) showed that the protolith ages of the rocks from this domain range between 2.8 and 2.2 Ga, which were possibly derived from adjoining Indian cratons, although a similar source was available in East Antarctica (e.g. Lambert Terrane: Mikhalsky et al. 2010). Hf isotopic studies by Upadhyay et al. (2009) documented juvenile provenance ranging in age between 2.7 and 1.9 Ga, broadly coinciding with the Nd isotopic data of Rickers et al. (2001). ...
The Eastern Ghats Belt (India) bears testimony to the assembly and dispersal of both the
Columbia and Rodinia supercontinents, and possibly the formation of East Gondwana. The belt
itself is a collage of different lithotectonic and isotopic domains, and therefore the petrological evolution
of each domain is to be considered separately prior to the formation of the belt. In this paper,
we present an updated review on the petrological and tectonic evolution of the different domains
along with geochronological constraints. We develop tectonic models to show how different lithotectonic
domains fit into supercontinent cycles in the Proterozoic period.
... Lambert Complex of the Rauer Group contains orthogneissic protolith of dominantly ca. 2450-2100 Ma age along with paragneisses Corvino et al., 2008;Mikhalsky et al., 2006Mikhalsky et al., , 2010 which is somewhat similar to that of Domain 3 as Rickers et al. (2001) showed that Domain 3 received materials from ca. 2200-1800 Ma orthogneissic and paragneissic sources. Incidentally the rocks of Lambert Complex were strongly deformed and metamorphosed at ca. 950 Ma and ca. ...
The Eastern Ghats Belt (EGB) witnessed orogenic activities during the Proterozoic time. The northern part of EGB is characterized by ca. 1000 Ma UHT metamorphic event followed by ca. 950 Ma reworking during compressive regime. This latter event also in EGB also provides crucial link to model the India-east Antarctica connection during the final amalgamation of Rodinia. However, the exhumation of UHT metamorphosed deep crust is an unresolved issue and it requires a comprehensive deformational-petrological-geochronological (P-T-t-D) study. The present work is done on the granulites exposed near the Chilka Lake anorthosite complex, northern EGB. The grossly migmatite rock association comprises of high-grade paragneisses and orthogneisses showing complex and multiple stages of folding and foliation/lineation development. The metamorphic history of the granulites is best recorded in the aluminous granulite that contains two contrasting mineral assemblages. The earliest (M1-D1) stage of metamorphism is identified by the development of a sillimanite-quartz-plagioclase-biotite foliation within garnet porphyroblasts. Subsequent M2-D2 event produced the peak granulite assemblages represented by Opx+Grt+Pl+Crd+Kfs+Qtz+Rt and Grt+Sil+Kfs+Pl+Qtz in two different bulk compositions at T = 900-950°C, P = 8.0-8.5 kbar. The gneissic foliation is further folded during the M3-D3 event and the axial planar S3 fabric is tectonically transposed parallel to S2 to form the regional structure of the area. Garnet porphyroblasts show decomposition to symplectic intergrowth of Opx+Crd+Spl and Spr+Crd in the former assemblage whereas Spl+Crd+Bt is formed in the latter; all attest to near-isothermal decompression to T = 700-800°C, P = 6.0-6.5 kbar. The appearance of contrasting intergrowth assemblages during M3-D3 stage can be explained by the variation of the bulk composition as evident from the chemistry of garnet and associated intergrown phases. M4 stage cooling produced late biotite-bearing assemblages. Local occurrence of intergrowth consisting granular Opx+Crd+Kfs replacing late biotite implies incipient granulite-grade reworking during M5 stage. Fluid-inclusion data suggest the presence of high-density CO2-dominated fluid during the peak M2-D2 stage, while the fluid regime changed to low-density mixed CO2-H2O (-N2-CH4) one during the M3-D3 stage. Zircon U-Pb SHRIMP data show prominent event of zircon growth during ca. 780 Ma (within a spread of 760-800 Ma) followed by a spread of near-concordant data in the time span of ca. 740-600 Ma. Texturally constrained monazite U-Th-Pb EPMA data, on the other hand, show two distinct ages for monazite growth. Monazite occurring within garnet porphyroblasts yield a group age of ca. 988+23 Ma from the data point analyzed from the grain interior, whereas the exterior part in contact of garnet show younger spot ages. Monazite occurring within quartzofeldspathic matrix also yields spot ages in the latter mentioned range and combining both sets of data, a group age of 742+15 Ma is obtained. Few spots with younger dates in the range of 550-500 Ma are also noted. We interpret that the ca. 990 Ma could possibly imply the timing of the M2-D2 event the signatures of which is not preserved in the analyzed zircon grains. The M3-D3 event is the most prominent event that occurred in the time frame of ca. 780 Ma. The spread of <740 Ma zircon as well as monazite data possibly implies large-scale redistribution of U, Th and Pb isotopes due to interaction with aqueous fluid. This interpretation is in sharp contrast to the suggested tectonothermal event in Chilka during 690-660 Ma as argued by earlier workers. Our data further show that the two adjacent crustal domain of EGB (Domains 2 and 3) shared similar histories at least up to ca. 1000 Ma after which the tectonic development of the northern EGB witnessed a paradigm shift. The ca. 780 Ma decompression event in the northern EGB opens up new possibilities for interpreting the breakup of Rodinia.
... Lambert Complex of the Rauer Group contains orthogneissic protolith of dominantly ca. 2450-2100 Ma age along with paragneisses Corvino et al., 2008;Mikhalsky et al., 2006Mikhalsky et al., , 2010 which is somewhat similar to that of Domain 3 as Rickers et al. (2001) showed that Domain 3 received materials from ca. 2200-1800 Ma orthogneissic and paragneissic sources. Incidentally the rocks of Lambert Complex were strongly deformed and metamorphosed at ca. 950 Ma and ca. ...
High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1-M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900-950°C, 8.5-9.0 kbar. The third metamorphic event caused decompression of the deeper crust up to 700-800°C, 6.0-6.5 kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2-H2O during the M3. Zircon U-Pb SHRIMP data suggest 781±9 Ma age for M3 event. Texturally constrained monazite U-Th-Pb EPMA data, on the other hand, yield a group age of 988±23 Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550-500 Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P-T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P-T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780 Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.
... This is interpreted as the age of amphibolite metamorphism in the Mount Creswell region, indicating that these rocks are part of the Beaver terrane. Our preliminary data suggest that the Ruker, Lambert and Beaver terranes amalgamated before peak metamorphism at 1000-900 Ma in the Beaver terrane, challenging the widely held view that there is a Cambrian suture in the Prince Charles Mountains and consistent with arguments that the Prince Charles Mountains might have assembled at ~1.0 Ga (Phillips et al., 2009;Mikhalsky et al., 2010). ...
Fossil testudinids are known in Europe since the Eocene. As well as relatively small taxa (usually < 30 cm in length), the European record includes several taxa of medium and large size. The largest size is achieved by several Neogene taxa, mainly early Miocene and Pliocene. The description of new specimens and a review of the previously published ones have allowed us to gain a better understanding of the morphology of the European large testudinids and to recognize that all these large taxa are part of a monophyletic lineage. However, we have identified a new European species, coming from levels near the Miocene–Pliocene limit that cannot be assigned to that lineage. This new taxon shares several characteristics with the extant African Centrochelys sulcata. The African lineage of Centrochelys has been recognized from pre-Messinian levels (Lapparent de Broin et al., 1999; Gmira et al., 2013).
The Messinian salinity crisis is one of the most important events in the history of the circum-Mediterranean area, causing major changes in the paleogeography and affecting the faunal assemblages in latest Miocene times, for example enabling the migration of representatives of the African fauna into Europe. The interaction between Europe and Africa has been demonstrated based on large and small mammal species, but so far there has been no evidence regarding the chelonian assemblages. The hypothesis proposing this new European tortoise as an African immigrant is evaluated here.
... Geological summary and geochemistry of metamorphic rocks in the northern PCMs This area was distinguished as a tectonic entity by Tingey (1982), and its structure and origin have remained the subject of much debate ever since (Kamenev et al. 1993;Mikhalsky et al. 2006aMikhalsky et al. , 2010. Based on lithological data, as well as a few Rb -Sr whole rock and U -Pb (TIMS) zircon ages, Kamenev et al. (1993) and Mikhalsky et al. (2001) distinguished two metamorphic complexes: the Beaver Complex (belt or terrane), largely composed of felsic granulites in the north, and the Fisher Complex (belt or terrane), largely composed of mafic amphibolites in the south (Fig. 2). ...
Within the Rayner Province in the Lambert Glacier area, two Proterozoic lithotectonic zones are distinguished, which differ in age and lithology. In the Fisher Zone, a significant juvenile component (ε Nd ( t )=+2 to +4) is represented by mafic, intermediate and felsic plutonic and volcanic rocks; the tectonomagmatic processes were concentrated at c. 1400–1200 Ma. In the Beaver Zone, orthogneisses record multiple emplacement, metamorphism and ductile deformation at c. 1150–930 Ma. New U–Pb SHRIMP-II zircon ages ( c. 1140 Ma and 1095 Ma – protolith emplacement; c. 950–850 and c. 540 Ma – metamorphism), chemical and Sm–Nd isotopic data indicate that both zones have their continuations in the eastern Amery Ice shelf coast. The Rayner Province has some geological features in common with the Albany-Fraser Orogen in Western Australia, suggesting that these regions evolved in similar tectonic environments at c. 1400–1300 Ma, followed by steady closure, from east to west, of the ocean that separated the Mawson Continent from Western Australia.
Supplementary material
Chemical compositions of rocks, a summary of trace element ratios, a summary of published U–Pb dates, field photo views, new U–Pb analyses by SIMS SHRIMP-II and new Sm–Nd data are available at www.geolsoc.org.uk/SUP18621
... However, a Rb-Sr age of ca 1360 Ma obtained by K.D. Collerson (personal communication to J.W. Sheraton; the data have apparently not yet been Aitken et al. (2014). Numbers indicate typical U-Pb zircon ages (from Fitzsimons, 2003, Mikhalsky et al., 2010, Bose et al., 2011, Veevers, 2012. Angular brackets indicate inherited zircons. ...
In this paper we present new U − Pb zircon age, Sm–Nd isotopic and chemical composition data for rocks cropping out in a few isolated nunataks in Wilhelm II Land in East Antarctica, namely Mirny oasis, Mt Brown and Gaussberg volcano, which contains xenogenic crustal material. These outcrops were subjects of geological investigations during the Soviet Antarctic Expedition of 1956–1957. Our data show that this region is underlain by a uniform crust which experienced a high-grade metamorphic event at ca 980 − 920 Ma, co-eval with the Rayner Orogeny in Kemp Land and the northern Prince Charles Mountains. Extensive indications of a ca 500 Ma event in coastal areas (granitoid intrusions in Mirny oasis and inherited zircons found in Gaussberg volcano), together with the lack of indications of this age in Mt Brown, point to a concentration of ca 500 Ma processes (roughly co-eval with the Prydz Orogeny) in the coastal part of Wilhelm II Land and their attenuation inland. We also determined a ca 1480 Ma age for a mafic magmatic protolith in Mt Brown which may be correlated with roughly co-eval orthogneiss in the Bunger Hills area. These observations suggest the conjugate positions of these crustal blocks in the early Mesoproterozoic and argue against a Cambrian suture running between them. In Gaussberg volcano a range of zircon 206Pb/238U ages of ca 320 Ma, ca 500 Ma, ca 980 Ma, and ca 2000–1800 Ma has been determined. The presence of ca 2000–1800 Ma zircons indicates involvement of mid-Palaeoproterozoic rocks in the structure of Wilhelm II Land. This argues for possible conjugation of this region with other East Antarctic blocks experienced the Palaeoproterozoic tectonic evolution and which have been considered to comprise the Mawson palaeocontinent.
... This is interpreted as the age of amphibolite metamorphism in the Mount Creswell region, indicating that these rocks are part of the Beaver terrane. Our preliminary data suggest that the Ruker, Lambert and Beaver terranes amalgamated before peak metamorphism at 1000-900 Ma in the Beaver terrane, challenging the widely held view that there is a Cambrian suture in the Prince Charles Mountains and consistent with arguments that the Prince Charles Mountains might have assembled at ~1.0 Ga (Phillips et al., 2009;Mikhalsky et al., 2010). ...
The genus Syringoalcyon was named in 1945. Its taxonomic assignment as well as its ecologic
implications have been a matter of discussion for a long time. Detailed morphological,
microstructural, nanostructural, geochemical and crystallographic analyses allow a closer
approach to characterization of Syringoalcyon. Samples from several locations and ages (Canada
to Morocco; Silurian to Carboniferous) have been studied by means of optical petrography using
thin and ultrathin sections, scanning electron microscopy, atomic force microscopy, electron
microprobe analysis and computer-integrated-polarization. The coral wall and the “epithecal
scales” show conspicuous characteristics:
Size: scales are larger than any other element known in Palaeozoic corals.
Microstructure continuity: the coral wall is characterized by a continuous frame composed of skeletal
elements (lamellae and fibres), which behave as a continuous structure. Microcrystalline elements
change gradually between the different morphologies, adapting their c-axes progressively.
However the step from lamellae to scales is abrupt.
Nanostructure: nanostructural elements of the scales have different shapes and sizes, whereas the
nanocrystalline elements of the Syrigoporicae keep the same form and size.
Mineralogy: The coral wall is low-Mg calcite except for some altered crystals located just in the
wall edges. On the other hand, the scales were originally high-Mg calcite. Some diagenetic
alterations have been observed in the skeletal elements but it is clear that these alterations did
not completely obliterate the structural and crystallographic properties, and some original
regions and their biogenic properties have been preserved.
This body of data implies that Syringoalcyon is a commensalistic or mutualistic association
between Syringopora and an epibiont. The analyses and the shape and distribution of the scales
also suggest that the epibiont was an Alcyonarian that attached to the syringoporoid, probably
for protection and proximity to sources of nutrients.
Literature references to epithecal scales in the Silurian seem to relate to a similar association of
coral and Alcyonarian, but the size and shape of scales clearly differ from the Carboniferous
ones. All the reliable Carboniferous records of the association are from the Upper Mississippian
of Palaeotethys, mainly in the northern border of Gondwana (Morocco and SW Spain).
... Taking these points together, we suggest that the Rayner Complex-Eastern Ghats represented a continental arc that we infer remained ocean-facing until the main phase of orogenesis at ca. 990-900 Ma (Fig. 13B). At this time the juvenile island arc rocks of the Fisher Terrane (Beliatsky et al., 1994;Mikhalsky et al., 1996Mikhalsky et al., , 1999 and the markedly older continental rocks of the Lambert Terrane (Boger et al., 2001Corvino et al., 2008Corvino et al., , 2011Mikhalsky et al., 2006Mikhalsky et al., , 2010 were accreted to the southern margin of the Rayner Complex. Although neither terrane is particularly large, we suggest that the collision of these small oceanic and continental terranes effectively terminated subduction along the Rayner-Eastern Ghats margin (Fig. 13B). ...
Complexly deformed gneisses in the Larsemann Hills, southern Prydz Bay, are customarily divided into a basement igneous complex (Søstrene Orthogneiss) and overlying metasediments (Brattstrand Paragneiss). New ion microprobe U–Pb zircon ages support this geological model and provide further age constraints for sediment deposition at ca. 1000 Ma and high-grade metamorphism at ca. 900 Ma. U–Pb zircon data for the Søstrene Orthogneiss, a prominent unit of the basement complex, indicate an igneous protolith age of 1126 ± 11 Ma. The igneous protolith of the Blundell Orthogneiss was emplaced at 968 ± 13 Ma. The Tassie Tarn Metaquartzite, a unit of the Brattstrand Paragneiss, has an estimated maximum depositional age of 1023 ± 19 Ma based on the weighted mean 207Pb*/206Pb* age of 1023 ± 19 Ma for the three youngest recognized detrital zircons, whereas the oldest inheritance is 2.54 Ga. Metamorphic rims on the detrital zircons define a broad discordia array between ca. 900 Ma and ca. 530 Ma which is interpreted to reflect metamorphic zircon growth or resetting at these times. Magmatic zircons in the Søstrene orthogneisses have narrow ranges of initial ɛHf (−2.8 to +3.6) and Hf model ages (TDM2 1.53–1.93 Ga), compared with much wider ranges (ɛHf = −16.4 to +6.6, TDM2 1.44–2.91 Ga) recorded in detrital zircons of similar age in the Tassie Tarn Metaquartzite. This allows a partial provenance link between Søstrene-type basement and overlying metasediments but suggests additional sedimentary contributions to the metaquartzite from older crustal sources. Such contributions may be represented in the metaquartzite by the older detrital zircons, which have significantly older Hf model ages (TDM2 2.45–2.91 Ga). A contribution from older crust is consistent with Nd isotope evidence for the Tassie Tarn Metaquartzite which has Nd model ages (TDM2) near 2.0 Ga, similar to Brattstrand Paragneiss in general, and older than Nd model ages in Søstrene Orthogneiss (TDM2 ca. 1.7 Ga). Relative age relationships between the Blundell Orthogneiss and Tassie Tarn Metaquartzite have been obscured by deformation, but our U–Pb zircon results permit Blundell Orthogneiss to be younger than the Brattstrand Paragneiss. Zircon Hf (ɛHf −1.0 to −3.7, TDM2 1.83–1.95 Ga) and whole rock Nd (ɛNd = −3.0 and −5.9; TDM2 1.77–1.98 Ga) isotopic data for the former allow the igneous protolith for this orthogneiss to be derived by partial melting or assimilation of both Søstrene Orthogneiss and Brattstrand Paragneiss.The rocks exposed in southern Prydz Bay bear similarities with those exposed the northern Prince Charles Mountains and we argue these regions probably represent a contiguous terrane, albeit with differing degrees of early Cambrian overprinting. We suggest that precursors of the Brattstrand Paragneiss were deposited in a back-arc basin located inboard of a ca. 1000 Ma continental arc that was active along the leading edge of the Indo-Antarctic craton. Collision with the Australo-Antarctic craton (ca. 530 Ma) merged these rocks into Gondwana and sutured them into their present position in Antarctica.
... On the other hand, similar source was also existed in other fragments of Columbia (e.g. Lambert Terrane, east Antarctica; Mikhalsky et al., 2010). ...
We present possible tectonic models for two crustal domains of the Proterozoic Eastern Ghats Belt, India based on recent petrological, geophysical and geochronological data. Although both the domains presently expose deep crustal sections, they evolved in two distinct time segments of the Precambrian through accretion–collision processes. This is why we argue that no unique model can explain the complexities of the belt. The southern part of the belt evolved through subduction-dominated accretionary processes encompassing India, east Antarctica, Australia and Laurentia as part of supercontinent Columbia during the span of ca. 1.90–1.60 Ga. To the contrary, the central domain witnessed a prolonged accretion–collision history initiated at ca. 1.50 Ga and culminated at ca. 0.90 Ga with the formation of supercontinent Rodinia. The latter united cratonic India with east Antarctica as a separate continent Enderbia that existed until about ca. 0.50 Ga. The pre-1.50 Ga history of this domain is ambiguous at the present state of knowledge. The northern domain has a much younger (ca. 0.90–0.50 Ga) tectonothermal history which is unrelated to either of the studied domains. The present models explain the reported petrotectonic processes including the ultra high temperature metamorphism in both the domains. The episodic growth of the Eastern Ghats Belt matches with Proterozoic supercontinent cycles.
... Data from Condie and Aster (2010), Kinny et al. (1993Kinny et al. ( , 1997, and Mikhalsky et al. (2010). Summary of tectonothermal evolution of the Vestfold Hills constructed by combining the metamorphic evolution described in Zulbati and Harley (2007), age of magmatism from Snape et al. (1997) and Black et al. (1991), and the metamorphic and detrital datasets acquired in this study. ...
The Vestfold Hills terrane in East Antarctica is a granulite facies terrane that preserves a record of sedimentation, magmatism and metamorphism that differs significantly from the other Archaean terranes exposed in East Antarctica. Sensitive High Resolution Ion Mass Spectrometry (SHRIMP) U-Pb isotopic data from detrital zircon cores, metamorphic rims and metamorphic zircon and monazite from the granulite facies Chelnok and Taynaya Paragneisses that demonstrate Archaean ages that are incompatible with the established ages of other East Antarctic source regions. The original sediments to the Chelnok and Taynaya Paragneisses were deposited between c. 2575 and c. 2520 Ma and underwent a protracted period of high-grade granulite-facies metamorphism from c. 2520 to c. 2450 Ma that is synchronous with the emplacement of the tonalitic Mossel Gneiss and the granitic to gabbroic rocks of the Crooked Lake Gneiss Group. The distinctive detrital zircon age populations and the period metamorphism recorded by the Vestfold Hills paragneisses lead us to speculate that: (1) these rocks were sourced from, and deposited on the margin of the crystalline basement to the North China Craton at the end of the Archaean, and (2) they underwent a period of high-grade metamorphism related to orogenesis driven by the collision of the North China Craton with the Archaean nucleus of South India during the late-Archaean to early-Paleoproterozoic.
... Standard spectrometers for LIBS typically have a resolution of ∼100 pm FWHM, which is insufficient for isotope measurements. In addition to measurements of special nuclear material, high-resolution LIBS may be useful in isotopic measurements for space exploration and geochronology [11][12][13][14][15][16][17][18][19][20][21]. Having access to high-resolution spectrometers will allow LIBS research to be conducted in these fields. ...
A Fabry–Perot etalon was coupled to a Czerny–Turner spectrometer to acquire high-resolution measurements in laser-induced breakdown spectroscopy (LIBS). The spectrometer was built using an inexpensive etalon coupled to a standard 0.5 m imaging spectrometer. The Hg emission doublet at 313.2 nm was used to evaluate instrument performance because it has a splitting of 29 pm. The 313.2 nm doublet was chosen due to the similar splitting seen in isotope splitting from uranium at 424.437 nm, which is 25 pm. The Hg doublet was easily resolved from a continuous-source Hg lamp with a 2 s acquisition. The doublet was also resolved in LIBS spectra of cinnabar (HgS) from the accumulation of 600 laser shots at rate of 10 Hz, or 1 min, under a helium atmosphere. In addition to the observed splitting of the 313.2 nm Hg doublet, the FWHM of the 313.1844 nm line from the doublet is reported at varying helium atmospheric pressures. The high performance, low cost, and compact footprint make this system highly competitive with 2 m double-pass Czerny–Turner spectrometers.
Compositions of mineral dust in ice cores serve as tracers of paleo-atmospheric circulation patterns, providing linkages between sources and sinks. Here we document the geochemical makeup of dust reaching continental West Antarctica, on late Holocene samples from the Siple Dome A ice core (spanning ∼1030–1800 C.E). The Nd–Sr isotope signature is unusual for Antarctic ice core dust samples. Siple Dome data are characterized by low Nd isotope ratios (as low as εNd = −16.3) along with low Sr isotope ratios (highest ⁸⁷Sr/⁸⁶Sr = 0.7102) compared with other Antarctic dust signatures. A well-defined inverse correlation between Sr–Nd isotope ratios indicates two primary mixing sources. The low εNd-values indicate involvement of ancient (Archean-to-early Proterozoic) continental crust, as either the direct source or as a precursor of the source, and the low Sr-values require low Rb/Sr ratios that often reflect high-grade metamorphism. The known Antarctic terrane with these characteristics is parts of Enderby Land, nearly at the opposite end of Antarctica. The isotopic signature of the second end-member is compatible with West Antarctic volcanoes or Patagonia in South America. The Sr–Nd isotopes and trace element abundances are also chemically compatible with mixing between volcanic material from Gaussberg, a small lamproite volcano in Kaiser Wilhelm II Land in coastal East Antarctica whose source is ancient lithospheric mantle, with dust from Patagonia or material from West Antarctic volcanoes. We assess these potential mixing scenarios and conclude that Siple Dome's unusual geochemical signature can best be explained by a mixture of Patagonian dust and a Gaussberg-like source, with additional minor contributions from old eroded Archean-to-early Proterozoic bedrock sources such as those in Enderby Land. Moreover, Siple Dome dust compositions are distinct from dust deposited on Taylor and Clark Glaciers in the McMurdo Dry Valleys of the western Ross Sea, precluding the Dry Valleys as a late Holocene dust source to this region of the eastern Ross Sea.
Remnants of ancient orogenic events provide a synoptic view on the Supercontinent amalgamation and breakup and hence enhance our understanding related to continental evolution. The Neoproterozoic Era is known to have registered rapid continental-scale movements and archived at least two major grouping of formerly dispersed continents known as Rodinia and Gondwana. The assembly of Rodinia and Gondwana is marked by the Grenvillian (~1000 Ma) and the Pan-African (500 Ma) events, respectively, which are well-recorded across continents. Present work attempts to characterize the time frame separating the two orogenic events by investigating the two widely spaced domains of India and Antarctica to understand the continental reconstructions of the Neoproterozoic era. Both these domains have reported Grenvillian orogenic event, however, the time span from Rodinia to Gondwana amalgamation remains enigmatic.
Domain 1 is part of the north-western Indian shield. Towards the southern end of the Grenvillian aged Delhi Fold Belt, a NW-SE trending magnetic anomaly, at high angle to the NNE-SSW ‘Delhi trend’, is recorded by a recent geophysical survey. Various granitic outcrops belonging to the Erinpura granite suite and an argillaceous-calcareous metamorphosed sequence of the Sirohi group, present near the Revdar town are examined. The petrographic and geochemical characteristics of the Erinpura granites have also been studied in context of the focus of the present work. Presence of amphibole bearing granite, besides other types, confirms the intermixed I-type characteristics. Orogenic characteristics of Erinpura granites is ascertained by strontium-neodymium isotopic analyses (87Sr/86Sr and 143Nd/144Nd). Mixing of three contrasting crustal components successfully explains the isotopic compositions of the granites and throws light on the continental orogenic magmatism which followed the Delhi orogeny. The Revdar metasedimentary sequence is deposited over the post-Delhi granitic basement. Investigation of the Revdar metapelite indicates presence of an upper-amphibolite grade metamorphic assemblage developed at 831±13 Ma which was partially reset at 718±34 Ma as estimated from chemical geochronology of texturally constrained monazite. The granites are dated to be 892±10 Ma and this age was partially reset at 815±43 Ma i.e. around the time of the younger Sirohi orogeny. The partial resetting of the Revdar metapelite can be ascribed to the extensive anorogenic Malani eruption that manifests the Rodinia breakup. An attempt is also made to decipher relationship of Erinpura granite emplacement to the older Delhi orogeny as well as the younger Sirohi orogeny. It is contended that the Rodinia break-up marked by MIS was preceded by an orogenic event which is reported during this work for the first time.
Domain 2 is Princess Elizabeth Land (PEL) of East Antarctica. It is one of the least explored inland sectors of East Antarctic shield, specifically in terms of sub-ice geology. Svenner Islands-Brattstrand Bluffs-Larsemann Hills constitutes ~70 km long coastal outcrops of PEL comprising complexly deformed and interlayered metapelites and orthogneisses. Investigations of pelitic granulites from these outcrops indicate high to ultra-high temperature (800-950°C) at low to medium pressure (2-5 kbar; exceptionally 10 kbar) conditions of metamorphism. A high pressure (~10 kbar) relict metamorphic event is inferred by using cordierite poor assemblage as a barometer, which is validated by the presence of rutile (present as inclusion in ilmenite) bearing field at high pressure in Effective Bulk Constrained (EBC) pseudosection modelling. Extensive development of cordierite coronas around restite phases and pseudosection analyses suggests a strong component of decompression of ~5kbar. Two set of ages are estimated (~700-800 Ma and ~500 Ma) by using chemical geochronology of texturally constrained monazites, corresponding to Tonian and Pan-African metamorphic events, respectively. Field data, petrographic studies and ages estimated from orthogneiss samples from the Brattstrand Bluffs and Grovnes Peninsula suggest that the orthogneiss unit is a product of in-situ melting of the pelitic granulites. It is proposed that the PEL and the Eastern Ghats Mobile Belt represent a contiguous terrane with two major orogenic imprints, reflecting Rodinia and Gondwana amalgamations. An attempt is made to mark out paleo-orogenic belt axes supported by both field as well as recent aero-magnetic signatures in interior PEL. Presence of a thinned lithosphere along the system of subglacial lakes-canyons confirmed by ICECAP/PEL consortium, in sub-ice PEL is interpreted.
Analog modelling is used to demonstrate influence of pervasive mechanical anisotropy of the basement in defining orientation of this rift system and its connection to the Lambert Graben.
This work substantiates evidence of swift configurational changes from Rodinia assembly to Gondwana amalgamation in Indo-Arabian as well as Indo-Antarctic terrains. It specifically highlights the geodynamic importance of a hitherto poorly recognized ~800 Ma orogeny in both the domains.
The Sandow Group in the Denman Glacier area consists of low-grade supracrustal (post-cratonic) strata. Such rocks are scarce and poorly studied in East Antarctica, but are significant for a better understanding of the geological history and tectonic evolution of the Precambrian supercontinents. We report U–Pb (LA-ICP-MS) detrital zircon ages which mostly fall into two groups of ca 1350−900 Ma and ca 1800−1500 Ma, which correspond to those of crystalline rocks exposed in the western Australo-Antarctica. The youngest zircons with magmatic zoning yield ages of ca 950–900 Ma which define the maximum age of sedimentation. Chemical and neodymium isotopic compositions of the Sandow Group rocks indicate derivation from a Proterozoic largely granitic source region. High-Ti mafic volcanic activity accompanied sedimentation, and therefore the Sandow Group should be considered a volcanic-sedimentary succession. The Sandow Group was presumably accumulated in a continental (pull-apart?) basin formed in the Neoproterozoic in relation to proto-Darling Fault system activity with its continuation into Antarctica. The Sandow Group may have its correlatives in Western Australia where sedimentary successions (e.g., Moora and Badgeradda Groups) occur along the proto-Darling Fault system.
The Rauer Islands and neighbouring Vestfold Hills are intruded by numerous mafic dykes. In the latter area the dykes are basically not deformed, albeit metamorphosed in the southwestern part, whereas in the former they are strongly deformed and metamorphosed. In Scherbinina Island they intrude Archaean rocks and their ages are between ca. 2800 Ma and ca. 530 Ma, while in Efremova, Filla, and Hop islands they intrude Mesoproterozoic ca. 1150 Ma or ca. 1000 Ma orthogneiss and pre-date ca. 1000–950 Ma tectonism. A comparison and possible correlation between dykes in the Rauer Islands and the Vestfold Hills is a crucial point in the interpretation of the regional tectonic evolution. We present ICP-MS analyses of trace elements and Nd isotopic data for mafic dykes from Rauer Islands and Vestfold Hills. Two chemically distinct dyke groups are distinguished in the Rauer Islands: low-LILE group which was sampled from Scherbinina, Efremova and west Filla islands, and high-LILE group which was sampled only from Hop and central Filla islands. The low-LILE dykes were emplaced into ca. 1150 Ma orthogneisses and more ancient rocks, but were not found within ca. 1000 Ma orthogneisses, whereas the high-LILE dykes intrude ca. 1000 Ma orthogneiss, but were not found within Archaean rocks. The low-LILE group displays many chemical and Nd isotopic features in common with high-Fe mafic dykes in the Vestfold Hills, but the age uncertainties preclude a correlation. The formation of the high-LILE mafic dykes in the Rauer Islands indicates magmatism in late-orogenic environments at the end of the Rayner Orogeny. Our data argue against direct correlation between mafic dykes in Rauer Islands and Vestfold Hills, in spite of similar tholeiitic whole rock compositions. The Vestfold Hills dykes experienced cooling to the Sm–Nd systematic closure temperature by 790 Ma and subsequent shearing at ca 635 Ma (garnet – whole rock). Considering the data published elsewhere we interpret that the Vestfold and Rauer crustal blocks experienced shared tectonothermal histories since ca 950 Ma but may have been conjugated in the present positions only by the late Neoproterozoic due to horizontal transport along a major transcurrent shear zone.
The configuration of the Greater Indian Landmass was achieved during the late Proterozoic era (Grenvillian-age) through tectonic cycles involving cratonic blocks of India and East Antarctica in the broad framework of the assembly of the supercontinent Rodinia. Geological evidences are recorded from orogenic belts separating southern, northern and western cratonic blocks of India and its transcontinental neighbor East Antarctica. Eastern Ghats Belt of India played a pivotal role in the continental amalgamation process and it evolved in tandem with the Central Indian Tectonic Zone and the Aravalli Delhi Mobile Belt. We have collated geological and geochronological evidences from the cratonic blocks and the bounding orogenic belts to trace back the Grenvillian-age tectonics surrounding India and its eventual manifestation as the configuration of the Greater Indian Landmass. The status of the Greater Indian Landmass as a part of Rodinia is debated and unresolved issues are highlighted.
The Prince Charles Mountains (PCM)-Prydz Bay region in East Antarctica experienced the late Mesoproterozoic/early Neoproterozoic (c. 1000-900 Ma) and late Neoproterozoic/ Cambrian (c. 550-500 Ma) tectonothermal events. The late Mesoproterozoic/early Neoproterozoic tectonothermal event dominates the Rayner Complex and spreads over the main part of the Prydz Belt. This event includes two episodes (or stages) of metamorphism accompanying the intrusion of syn- to post-orogenic granitoids at c. 1000-960 Ma and c. 940-900 Ma. The c. 1000-960 Ma metamorphism in the northern PCM and Mawson Coast records medium- to lowpressure granulite facies conditions accompanied by a near-isobaric cooling path, whereas the c. 940-900 Ma metamorphism in Kemp Land reaches relatively higher P-T conditions followed by a near-isothermal decompression or decompressive cooling path. The late Mesoproterozoic/ early Neoproterozoic orogeny (i.e. the Rayner orogeny) involved a long-lived (c. 1380-1020 Ma) magmatic accretion along continental/oceanic arcs and a protracted or twostage collision of the Indian craton with a portion of East Antarctica, forming the Indian-Antarctic continental block independent of the Rodinia supercontinent. The late Neoproterozoic/Cambrian tectonothermal event pervasively overprinted on both Archaean-Proterozoic basements and cover sequences in the Prydz Belt. Except for high-pressure granulite boulders from the Grove Mountains, the metamorphism of most rocks records medium-pressure granulite facies conditions with a clockwise P-T path. In contrast, this event is lower grade (greenschist-amphibolite facies) and localized in the PCM. Regionally, the late Neoproterozoic/Cambrian tectonothermal event seems to have developed on the southeastern margin of the Indo-Antarctic continental block, suggesting that the major suture should be located southeastwards of the presently exposed Prydz Belt. The precise dating for different rock types reveals that the late Neoproterozoic/ Cambrian orogeny (i.e. the Prydz orogeny) commenced at c. 570 Ma and lasted until c. 490 Ma, which is roughly contemporaneous with the late collisional stage of the Brasiliano/ Pan-African orogenic systems in Gondwanaland. Therefore, the final assembly of the Gondwana supercontinent may have been completed by the collision of a number of cratonic blocks during the same time period.
The Prince Charles Mountains have been subject to extensive geological and geophysical investigations by former Soviet, Russian and Australian scientists from the early 1970s. In this paper we summarise, and review available geological and isotopic data, and report results of new isotopic studies (Sm-Nd, Pb-Pb, and U-Pb SHRIMP analyses); field geological data obtained during the PCMEGA 2002/2003 are utilised. The structure of the region is described in terms of four tectonic terranes. Those include Archaean Ruker, Palaeoproterozoic Lambert, Mesoproterozoic Fisher, and Meso- to Neoproterozoic Beaver Terranes. Pan-African activities (granite emplacement and probably tectonics) in the Lambert Terrane are reported. We present a summary of the composition of these terranes, discuss their origin and relationships. We also outline the most striking geological features, and problems, and try to draw attention to those rocks and regional geological features which are important in understanding the composition and evolution of the PCM and might suggest targets for further investigations.
The North Mawson Escarpment, in Antarctica’s Prince Charles Mountains, forms part of a Palaeoproterozoic crustal complex which separates Archaean cratonic material to the south from Early Neoproterozoic and Early Palaeozoic metamorphic belts to the north. It consists of nappe-like masses of grey gneiss and metasupracrustal rocks that were subjected to repeated ductile deformation under upper amphibolite to lower granulite facies metamorphic conditions. In this paper, we report zircon U–Pb dating results that constrain the principal tectonothermal events to the periods 2490–2420 Ma, 2180–2080 Ma, 940–880 Ma and 530–490 Ma. The magmatic precursors of volumetrically important grey gneiss were produced, and reworked at least partly, during the 2490–2420 Ma and 2180–2080 Ma events. The superimposition of these events is clearly documented by U–Pb ages from several composite zircons. The formation of associated metasupracrustals, possibly in a passive margin setting, occurred between the 2490–2420 Ma and 940–880 Ma events. Both grey gneiss and metasupracrustals were subsequently reworked during the 940–880 Ma and 530–490 Ma events, corresponding to the superposition of both the Rayner and Prydz Belts onto Palaeoproterozoic lithosphere of the Lambert Complex. Transposition and peak metamorphism preceded the intrusion of leucogranite dykes at 905 Ma and, based on metamorphic zircon growth at around 930 Ma in metapelitic schist, are related to the Rayner orogeny. It is suggested that the North Mawson Escarpment was assembled to most coastal regions of the Antarctic sector between 45° and 80°E by at least 900 m.y. ago.
Since the 1960s, the structure and age of the Antarctic crust has been the object of systematic study [1, 2, and others]. East Antarctica is an ancient platform, while the West Antarctica and Transantarctic Mountains are composed of different-age Phanerozoic fold systems. It was suggested that the basement of the Antarctic Platform was formed in the Early Precambrian (mainly in the Archean) and then subjected to intense and repeated tectonothermal activation without significant mantle input [3]. The geodynamic nature and role of the Mesoproterozoic (Grenvillian) and Neoproterozoic‐ Early Paleozoic (Panafrican) stages of tectonogenesis in the crustal growth of East Antarctica remain controversial problems. Russian geologists attributed processes of activation to the Mesoproterozoic stage [2, 3], whereas some foreign authors suggested that Queen Maud Land (Fig. 1) is a continuation of the Grenvillian orogenic belt of North America [4]. Panafrican tectonogenesis was interpreted either as an accretionary orogenic process [1] or an activation process [2, 3]. The role of juvenile material in the Grenville and Panafrican structures was not studied specially and remains one of the key problems in the geological structure of East Antarctica. This paper is the first attempt to reconstruct the evolution of the Antarctic crust by generalization of Sm‐Nd isotope data on ancient crystalline rocks and diverse granitoids of Antarctica and to distinguish the T DM model age provinces. The age of primary sialic matter formed by melting of mantle wedge above subduction zone can be estimated using Sm‐Nd isotopic systematics of the rocks [5]. The model Sm‐Nd isotopic age ( T DM ) is interpreted as the extraction age of juvenile material from the depleted mantle. Subsequent crustal reworking (metamorphism, anatexis, erosion, and sedimentation) had no significant effect on Sm‐Nd fractionation [6, 7], with preservation of the initial Nd isotopic characteristics. Identification of isotopic provinces and subdivision of the crustal blocks of other continents by the model Sm‐Nd age was carried out in the course of many special studies, for example [8‐10]. The T DM ages were calculated in this work in compliance with model [11] using the following parameters: 147 Sm/ 144 Nd DM = 0.2136, 143 Nd/ 144 Nd DM = 0.513151. The rocks with extreme 147 Sm/ 144 Nd values (more than 0.14 and less than 0.09) were omitted from consideration. One- and two-stage model ages for samples with Sm/Nd ratios of 0.09‐0.14 differ by no more than 100‐200 Ma, having no significance for further
In situ electron microprobe monazite dating and mineral equilibria modelling of amphibolite-granulite-facies metapelites from the southern Prince Charles Mountains, East Antarctica has been carried out to unravel the P-T conditions, spatial extent and structural style of two overprinting orogenic records. This study shows that: (1) rocks of the northern Palaeoproterozoic Lambert Complex were pervasively reworked at peak conditions (6·5-7·1 kbar and 790-810°C) during the Early Neoproterozoic Rayner orogenic event; (2) rocks of the southern Lambert Complex experienced pervasive deformation and metamorphism at peak conditions (5·8-6·1 kbar and 625-635°C) during Early Palaeozoic Prydz orogenic activity; (3) in regions of the Lambert Complex reworked during the Rayner orogenic event, Prydz-aged orogenesis was highly localized. The distribution of orogenic activity pertaining to the Rayner and Prydz orogenic events in the southern Prince Charles Mountains can be attributed to (1) the development of a southward directed (current coordinates) orogenic front that propagated from an Early Neoproterozoic collision between India and Antarctica, and (2) rock fertility (i.e. availability of free fluid) during Early Palaeozoic intraplate orogenesis that was driven by far-field stresses generated by a collision of India-Antarctica with the Mawson Craton. © The Author 2009. Published by Oxford University Press. All rights reserved.
The results of the Soviet geological mapping program in the Prince Charles Mountains (Australian Antarctic Territory) are presented as the first major publication of the Soviet mapping program from 1983 and 1991. Except for a map of Else Platform, the maps published in this paper represent all maps completed by the 28th to 35th Soviet Antarctic Expeditions in the Prince Charles Mountains. The maps cover four suggested tectonic provinces, the Beaver Belt, Lambert Province, Fisher Belt and Ruker Terrane. The four terranes show a continuous increase in metamorphic grade from south to north. The Ruker Terrane is of a greenschist and lower amphibolite facies metamorphic grade, the Lambert Province consists of retrogressively metamorphosed Beaver Belt granulite and prograde metamorphosed greenschist of the Ruker Terrane and the Beaver Belt consists of high grade granulite. The Fisher Belt is a greenstone belt which is interpreted to be thrust later against the Lambert Province. Rock‐types of all four terranes as shown on the maps are discussed and an up‐to‐date summary of the work completed by the Soviet Antarctic Expeditions in the Prince Charles Mountains is given.
Sensitive High Resolution Ion MicroProbe (SHRIMP) UPb zircon ages obtained from felsic intrusive bodies elsewhere within the northern Prince Charles Mountains. Early Palaeozoic activity at Mount Kirkby is restricted to the emplacement of minor planar pegmatites at 517 ± 12 Ma, which provide a maximum age for local development of discrete extensional mylonites. No conclusive evidence of tectonic or metamorphic events at c. 800 Ma and c. 500 Ma, which have been recently postulated for the region, can be identified from the presently available U–Pb zircon data.
The Sr–Nd–Hf isotopic compositions of both saprolites and parent rocks of a profile of intensively weathered Neogene basalt in Hainan, South China are reported in this paper to investigate changes of isotopic systematics with high masses. The results indicate that all these isotopic systematics show significant changes in saprolites compared to those in corresponding parent rocks. The 87Sr/86Sr system was more seriously affected by weathering processes than other isotope systems, with εSr drifts 30 to 70 away from those of the parent rocks. In the upper profile (>2.2m), the Sr isotopes of the saprolites show an upward increasing trend with εSr changing from ~50 at 2.2m to ~70 at 0.5m, accompanying a upward increasing of Sr concentrations, from ~10μg/g to ~25μg/g. As nearly all the Sr of the parent rock has been removed during intensive weathering in this profile, the upward increasing of Sr concentrations in the upper profile suggests import of extraneous Sr. Rainwater in this region, which enriches in Sr (up to 139μg/L) from seawater, may be the important extraneous source. Thus, the Sr isotopes of the saprolites in the upper profile may be mainly influenced by import of extraneous materials, and the Sr isotopic characteristics may not be retained. In contrast, the εNd and εHf of the saprolites drift only 0–2.6 and 0–3.7 away from the parent rocks, respectively. The negative drifts of the εNd and εHf are coupled with Nd and Hf losses in the saprolites; i.e., larger proportions of Nd and Hf loss correspond to lower εNd and εHf. Compared with the relative high Nd and Hf concentrations of the saprolites, the contributions of extraneous Nd and Hf both from wet and dry deposits of aeolian input are negligible. Thus, the εNd and εHf changes in the profile are mainly resulted from consecutive removal of the Nd and Hf. Calculation indicates that the 143Nd/144Nd and 176Hf/177Hf ratios in saprolites are all significantly lower than their initial values in the parent rock. Simply removing part of the Nd and Hf by incongruent decomposing some of the minerals may not account for this. Fractionation should be happen, which 143Nd and 176Hf may be preferentially removed from the profile relative to 144Nd and 177Hf during intensive chemical weathering, resulting in lower 143Nd/144Nd and 176Hf/177Hf ratios in saprolites relative to the parent rock, even though details for this process is not known. A positive correlation is observed between the εNd and εHf of the saprolites. Interestingly, the saprolites with a net loss of Nd and Hf in the upper profile show good positive correlation, and the regression line parallels the terrestrial array. By contrast, saprolites with a net gain of Nd and Hf in the lower profile generally show higher εHf values at a given εNd value, and the regression line between these εNd and εHf appears to parallel the seawater array. This supports the hypothesis that the contribution of continental Hf from chemical weathering release is the key to the obliquity of the seawater array away from the terrestrial array of the global εNd and εHf correlation. Our results also indicate that caution is needed when using εSr, εNd, and εHf to trace provenances for sediments and soils.
2 Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg, 2, Hannover 30655, Germany Abstract Mafic and ultramafic rocks occurring as lenses, boudins, and tectonic slabs within metamorphic units in the southern Mawson Escarpment display mantle characteristics of either a highly enriched, or highly depleted nature. Fractionation of these mantle rocks from their sources may be as old as Eoarchaean (ca 3850 Ma) while their tectonic emplacement probably occurred prior to 2550 Ma (U-Pb SHRIMP data). These results provide for the first time evidence for Archaean suturing within East Antarctica. Similar upper mantle sources are likely present in the northern Mawson Escarpment. A younger age limit of these rocks is 2200 Ma, as indicated by presumably metamorphic zircon ages while their magmatic age may be constrained by single zircon dates at 2450-2250 Ma. The area of the northern Mawson Escarpment is most likely of ensimatic origin and includes mafic rocks which were derived from distinct mantle source(s) during Palaeoproterozoic time. Citation: Mikhalsky, E.V., F. Henjes-Kunst, and N.W. Roland (2007), Early Precambrian mantle derived rocks in the southern Prince Charles Mountains, East Antarctica: age and isotopic constraints, in Antarctica: A Keystone in a Changing World - online Proceedings of the 10 th ISAES,
Summary: We present new geochemical and U-Pb zircon data on mafic dykes from the southern Prince Charles Mountains. The dykes crystallised at ca 1700 Ma and 1300-1350 Ma. Apparently the oldest (ca 2400 Ma) are high-Mg orthopyroxene-bearing dykes which are also known from the Enderby Land and the Vestfold Hills. Abundant younger dykes are variously enriched in the LILE and comprise low- and high-LILE geochemical groups, as do the dykes in the abovementioned areas. The dykes in the southern Prince Charles Mountains are roughly co-eval and compositionally identical to those reported from the Enderby Land and the Vestfold Hills and were derived from the same or quite similar mantle source(s). This suggests that these parts of East Antarctica were conjugated and behaved as a single continental landmass since the early Palaeoproterozoic and questions a widely accepted model of Pan-African amalgamation of these blocks.
This geochemical classification of granitic rocks is based upon three variables. These are FeO/(FeO + MgO) = Fe-number [or FeOtot/(FeOtot + MgO) = Fe-*], the modified alkali-lime index (MALI) (Na2O + K2O - CaO) and the aluminum saturation index (ASI) [Al/(Ca - 1.67P + Na + K)]. The Fe-number (or Fe-*) distinguishes ferroan granitoids, which manifest strong iron enrichment, from magnesian granitoids, which do not. The ferroan and magnesian granitoids can further be classified into alkalic, alkali-calcic, calc-alkalic, and calcic on the basis of the MALI and subdivided on the basis of the ASI into peraluminous, metaluminous or peralkaline. Because alkalic rocks are not likely to be peraluminous and calcic and calc-alkalic rocks are not likely to be peralkaline, this classification leads to 16 possible groups of granitic rocks. In this classification most Cordilleran granitoids are magnesian and calc-alkalic or calcic; both metaluminous and peraluminous types are present. A-type granitoids are ferroan alkali-calcic, although some are ferroan alkalic. Most are metaluminous although some are peraluminous. Caledonian post-orogenic granites are predominantly magnesian alkali-calcic. Those with <70 wt % SiO2 are dominantly metaluminous, whereas more silica-rich varieties are commonly peraluminous. Peraluminous leucogranites may be either magnesian or ferroan and have a MALI that ranges from calcic to alkalic.
Shaw massif is situated in the central part of the Prince Charles Mountains and represents a complex with complicated fold structure and compositions that include biotite leucogneisses, garnet-biotite gneisses and plagiogneises (Lambert gneisses); amphibole-biotite melanogneisses, garnet-biotite plagiogneisses (Shaw melanogneisses). Also, there are poorly developed garnet-sillimanite-biotite gneisses (Isabelle paragneisses) which are met in the form of xenolith bodies among the Lambert gneisses and could be the fragments of the ancient sedimentary layer. The obtained U-Pb data reflect the two main geological events with ages 900-1100 Ma and 450-550 Ma corresponding to Rayner and Pan-African tectonothermal events. The Shaw Massif terrane has been affected by at least 5 deformation events and three stages of metamorphic reworking. The structural geological position of the Shaw Massif region could be interpreted as a younger, high grade metamorphic region framing the Fisher Province.
We present new U-Pb zircon (SHRIMP) data on rocks from Mt Newton and Cumpston Massif in the southern Prince Charles Mountains. Our data demonstrate that Mt Newton was affected by a newly proposed Palaeoproterozoic "Newton" Orogeny at ca. 2100-2200 Ma. Sedimentation, felsic volcanism (ca. 2200 Ma), metamorphism and folding, followed by granite intrusion (ca. 2100 Ma), suggest development of a trough or aulacogene in the area during the early Palaeoproterozoic. An orthogneiss from Cumpston Massif yielded an age of ca. 3180 Ma for granitic protolith emplacement, which is in good agreement with many U-Pb zircon ages from similar rocks in the southern Mawson Escarpment. A syn- to late-tectonic muscovite-bearing pegmatite from Cumpston Massif yielded a ca. 2500 Ma date of emplacement, which indicates early Palaeoproterozoic activity in this block, probably in response to a tectono-magmatic episode in the Lambert Terrane bordering the Ruker Terrane in the northeast. The correlation of tectono-magmatic events in both the Ruker and Lambert terranes of the southern Prince Charles Mountains provides evidence for their common evolution during the Proterozoic.
Fisher Massif consists of Mesoproterozoic (c. 1300 Ma) lower amphibolite-facies metavolcanic rocks and associated metasediments, intruded by a variety of subvolcanic and plutonic bodies (gabbro to granite). It differs in both composition and metamorphic grade from the rest of the northern Prince Charles Mountains, which were metamorphosed to granulite facies about 1000 m.y. ago. The metavolcanic rocks consist mainly of basalt, but basaltic andesite, andesite, and more felsic rocks (dacite, rhyodacite, and rhyolite) are also common. Most of the basaltic rocks have compositions similar to low-K island arc tholeiites, but some are relatively Nb-rich and more akin to P-MORB. Intermediate to felsic medium to high-K volcanic rocks, which appear to postdate the basaltic succession, have calc-alkaline affinities and probably include a significant crustal component. On the present data, an active continental margin with associated island arc was the most likely tectonic setting for generation of the Fisher Massif volcanic rocks.
The Prince Charles Mountains have been subject to extensive geological and geophysical inves- tigations by former Soviet,Russian and Australian scientists from the early 1970s. In this paper we sum- marise, and review available geological and isotopic data, and report results of new isotopic studies (Sm- Nd, Pb-Pb, and U-Pb SHRIMP analyses); field geological data obtained during the PCMEGA 2002/2003 are utilised. The structure of the region is described in terms of four tectonic terranes. Those include Ar- chaean Ruker, Palaeoproterozoic Lambert, Mesoproterozoic Fisher, and Meso- to Neoproterozoic Beaver Terranes. Pan-African activities (granite emplacement and probably tectonics) in the Lambert Terrane are reported. We present a summary of the composition of these terranes, discuss their origin and relations- hips. We also outline the most striking geological features, and problems, and try to draw attention to tho- se rocks and regional geological features which are important in understanding the composition and evo- lution of the PCM and might suggest targets for further investigations. Previous Work The Prince Charles Mountains (PCM) constitute by far the best exposed cross section through the East Antarctic Shield, extending for over 500 km along the drainage basin of the Lambert Glacier - Amery Ice Shelf system (Fig. 2.7-1). Australian geologists first visited this region between 1955 and 1957. The results of geological observations were presented by Stinear (1956) and Crohn (1959), who recorded in the northern PCM (NPCM) a range of high-gra- de metamorphic rocks of both sedimentary and igneous origin, as well as orthopyroxene granitoids, and an overlying coal-bearing Permian-Triassic sedimentary sequence. Geological investigations in the southern PCM (SPCM) showed that the rocks there are generally of much lower metamorphic grade (green-schist to amphibolite facies) than those of the NPCM; they include thick metasedimentary sequences and are cut by abundant mafic dykes. The early workers (Tingey 1982, 1991, and references therein), on the basis of numerous Rb-Sr ages, reported the PCM as comprising two major tectonic provinces roughly corresponding to the two parts of the mountain range (NPCM and SPCM). One of the most interesting results of this study (Tingey 1982, 1991) was the recognition that presumed gra- nitic basement and overlying metasediments in the SPCM were of Archaean age (whole-rock Rb-Sr isochrons 2 700 ±90, 2 750 ±400, and 2 760 ±200 Ma), whereas granulite-facies rocks of the NPCM were Meso- to Neoproterozoic (whole-rock Rb-Sr isochrons from 769 ±36 to 1033 ±85 Ma). This was at vari- ance with earlier ideas that the higher-grade rocks were likely to be older (e.g., Solovev 1972). Muscovite-bearing pegmatites cutting the metasediments in the SPCM were dated at 2 589, 2 100, 1 995, and 1 708 Ma, and it was suggested that Palaeoproterozoic, as well as Archaean sequences may be present. A few imprecise Mesoproterozoic isochron ages were also obtained (ca. 1 170 ±230, 1 400 ±150 Ma); these were interpreted as reset ages, and provi-
The eastern Amery Ice Shelf (EAIS) and southwestern Prydz Bay are situated near the junction between the Late Neoproterozoic/Cambrian high-grade complex of the Prydz Belt and the Early Neoproterozoic Rayner Complex. The area contains an important geological section for understanding the tectonic evolution of East Antarctica. SHRIMP U–Pb analyses on zircons of felsic orthogneisses and mafic granulites from the area indicate that their protoliths were emplaced during four episodes of ca. 1380 Ma, ca. 1210–1170 Ma, ca. 1130–1120 Ma and ca. 1060–1020 Ma. Subsequently, these rocks experienced two episodes of high-grade metamorphism at > 970 Ma and ca. 930–900 Ma, and furthermore, most of them (except for some from the Munro Kerr Mountains and Reinbolt Hills) were subjected to high-grade metamorphic recrystallization at ca. 535 Ma. Two suites of charnockite, i.e. the Reinbolt and Jennings charnockites, intrude the Late Mesoproterozoic/Early Neoproterozoic and Late Neoproterozoic/Cambrian high-grade complexes at > 955 Ma and 500 Ma, respectively. These, together with associated granites of similar ages, reflect late- to post-orogenic magmatism occurring during the two major orogenic events. The similarity in age patterns suggests that the EAIS–Prydz Bay region may have suffered from the same high-grade tectonothermal evolution with the Rayner Complex and the Eastern Ghats of India. Three segments might constitute a previously unified Late Mesoproterozoic/Early Neoproterozoic orogen that resulted from the long-term magmatic accretion from ca. 1380 to 1020 Ma and eventual collision before ca. 900 Ma between India and the western portion of East Antarctica. The Prydz Belt may have developed on the eastern margin of the Indo-Antarctica continental block, and the Late Neoproterozoic/Cambrian suture assembling Indo-Antarctica and Australo-Antarctica continental blocks should be located southeastwards of the EAIS–Prydz Bay region.
The only remaining areas of pristine 3.6-2.7 Ga crust on Earth are parts of the Kaapvaal and Pillbara cratons. General similarities of their rock records, especially of the overlying late Archean sequences, suggest that they were once part of a larger Vaalbara supercontinent. Here we show that the present geochronological, structural and palaeomagnetic data support such a Vaalbara model at least as far back as 3.1 Ga, and possibly further back to 3.6 Ga, Vaalbara fragmented prior to 2.1 Ga, and possibly as early as 2.7 Ga, suggesting supercontinent stability of at least 400 Myr, consistent with Neoproterozoic and Phanerozoic analogues.
The structural and metamorphic evolution of the Precambrian Vestfold Block, eastern Antarctic (68o35'S, 77o85'E) reflects the effects of several periods of granulite facies metamorphism and a complex deformational history which involved a number of periods of folding. During the Early and Middle Proterozoic, the Vestfold Block was intruded by several major swarms of dolerite dykes. These are correlated on petrographic, geochemical and isotopic grounds with similar dykes in Enderby Land. Sr and Nd isotopic data indicate that gneisses in the Vestfold Block experienced at least 2 granulite facies tectonothermal events during the Archaean (ca 2800-3000 Ma and ca 2400-2500 Ma ago). South of the Vestfold Block, in the Rauer Islands, gneiss and dyke relationships show the effect of reworking (deformation and in situ anatexis) during a Late Proterozoic granulite facies event ca 1100 Ma ago.-from Authors
In the southern Mawson Escarpment, southern Prince Charles Mountains (Antarctica), lenses and blocks of compositionally highly diverse ultramafic and relatively rare mafic rocks are mostly confined to generally east-west trending high-strain shear zones. These rocks consist of amphibole (actinolite, tremolite, anthophyllite or, rarely hornblende), sporadically orthopyroxene, olivine and rarely dinopyroxene. Secondary talc, serpentine, epidote, phlogopite, carbonate, chlorite, and titanite are developed sporadically. Less sheared rocks include amphibole orthopyroxenite and amphibole dunite. The geochemical features of the ultramafic rocks point to a strong influence of accumulation processes. Sm-Nd whole rock and mineral separate data point to an origin from a highly heterogeneous Archaean mantle which comprises at least a highly depleted and an enriched component. The latter may represent a metasomatically reworked depleted reservoir. The LILE enrichment probably occurred already in the early Archaean. U-Pb zircon SHRIMP dating of zircon from a syn-tectonic leucocratic quartz-feldspar vein associated with the ultramafics in a high-strain shear zone yields ages of 2539 ± 61 Ma (lower intercept) and 3333 ± 60 Ma (upper intercept). The ca. 3.3 Ga date is interpreted as a close estimate of the age of syn-tectonic vein formation and thus also the formation of the high-strain shear zone while the ca. 2.5 Ga date probably reflects a (tectono-)thermal overprint. The occurrence of lenses and blocks of ultramafic and subordinate mafic rocks of highly variable lithological, geochemical and Sm-Nd isotope composition in high-strain shear zones of the soothern Mawson Escarpment is interpreted as a tectonic melange indicative of major deep-reaching crustal shear processes in Paleoarchaean times.
In the southern Prince Charles Mountains (SPCM) apparently undeformed post-tectonic granites are dated by zircon U-Pb (SHRIMP) study at c. 525-515 Ma. Early Palaeozoic granites in the SPCM may be correlated with peraluminous leucogranite type. Origination of these rocks as a result of voluminous mafic underplate at the base of the crust during the course of an intraplate orogeny is possible. Granites in some parts of the Ruker Terrane (Mts Dummett, Stinear, and Newton) contain inherited zircon populations with Palaeoproterozoic or Mesoproterozoic ages, which are not known from the Ruker Terrane. Granites in the Prydz Bay coast form two magmatic phases, the earlier one was pre- or syn-tectonic and is dated at c. 505 Ma. The later phase has A-type granite features (high HFSE, Ga/Al, biotite with high Fe, and F) and originated in within-plate tectonic setting.
Granitic rocks in the southern Prince Charles Mountains vary widely in both composition and field appearance. Generally, the granitoids form syn- to post-tectonic sheet-like bodies. Variously deformed (pre-tectonic) basement granitoids also occur as large bodies. Subvertical dykes occur in many localities, and sporadically form dense networks grading into larger bodies with only scarce rafts of the country rocks. In a few localities concentrated in the Fisher Glacier area stock-like bodies occur. The deformation style also varies widely. Variously deformed granitic bodies prevail in the northern Mawson Escarpment and nearly undeformed granites occur in the Fisher Glacier area. The granite structure varies from homogeneous, equigranular to augen or highly stretched gneissic. Two distinct gneissic rock groups occur in the southern Mawson Escarpment: biotite or hornblende-biotite granite-gneiss, and orthopyroxene-bearing granite-gneiss. The latter was probably formed during a charnockitisation process or may be magmatic, as no biotite break-down reaction has been preserved and some rocks reveal apparently magmatic structures. In the Cumpston Massif plagioclase-rich orthogneisses containing magnetite and fluorite occur. More calcic gneisses predominate in Clemence Massif. The presumed Early Palaeozoic granitoids form three distinct groups. The granites in the northern Mawson Escarpment are biotite and rarely biotite-garnet or biotite-hornblende-bearing, in Harbour Bluff mostly muscovite-garnet-bearing, and elsewhere in the southern Prince Charles Mountains mostly muscovite or muscovite-biotite-bearing. Distinctive granitic rocks crop out on Landing Bluff (Prydz Bay coast), where they are more mafic (biotite) and contain essential amounts of accessory allanite, titanite, and fluorite. These rocks cannot be correlated with granites in the southern Prince Charles Mountains, which suggests different origins for the granites in these two regions.
Laser ablation inductively coupled mass spectrometry (LA-ICPMS) dating of detrital zircon has been employed to tighten geochronological constraints from the southern Prince Charles Mountains, East Antarctica. The grains of detrital zircon are from extensive metasedimentary units that define different stratigraphic levels. Provenance information from this study has identified three lithostratigraphic units that range in age from Archaean to Neoproterozoic times. The newly defined Tingey Complex contains the oldest known strata, and consists of an Archaean felsic basement overlain by three stratigraphic layers, distinguished by ca. 3200 Ma, ca. 2800 Ma and ca. 2500 Ma detrital zircon grains. The Lambert Complex consists of a metasedimentary package, characterised by ca. 2100 Ma, ca. 1900-1800 Ma and ca. 2600 Ma detrital zircon grains that possibly overlies late Palaeoproterozoic orthogneiss. The Neoproterozoic Sodruzhestvo Group comprises the youngest exposed unit and consists of a thick, clastic-dorninated sequence that is distinguished by ca. 1170-970 Ma grains. This study suggests that the isotopic differences reported from the southern Prince Charles Mountains are a result of stratigraphic stacking, rather than due to juxtaposition via collision and accretion tectonics. The discovery of ca. 250OMa detrital zircon grains within the Palaeoproterozoic metasedimentary rocks of the Tingey Complex strengthens correlations with Archaean fragments exposed in neighbouring regions of East Antarctica. Constraining the deposition of the Sodruzhestvo Group to the mid-Neoproterozoic period suggests a prominent period of basin development occurred within the southern Prince Charles Mountains at this time. (c) 2006 Elsevier B.V. All rights reserved.
The Prince Charles Mountains consist mainly of a complex of Archean to upper Proterozoic metamorphic rocks, locally intruded by Cambrian granites and unconformably overlain by a small enclave of upper Permian sedimentary strata. Metamorphic grade ranges from greenschist to granulite facies, and at least two major metamorphism - one Archean, the other late Proterozoic - have been distinguished despite geologic, metamorphis, and isotopic complexities caused by the overprinting of the later metamorphism. The wide range of ⁸⁷Sr/⁸⁶Sr initial ratios obtained in geochronologic studies is interpreted as evidence that both major metamorphisms involved crustal formation and reworking processes. The Prince Charles Mountains provide probably the best cross section of the East Antarctic metamorphic shield and contain the only Archean cratonic block as yet identified in Antarctica. Comparisons with other parts of Gondwanaland reveal important similarities with Africa and SW Australia but few correlations with peninsular India and Sri Lanka, the areas most commonly juxtaposed against the Prince Charles Mountains area in Gondwanaland reassemblies. The research described in this paper demonstrates yet again that the highest grade metamorphic rocks in an area are not necessarily the oldest, and it highlights the importance of geochronology in studies of the East Antarctic shield.-Author
High-grade metamorphic and felsic igneous rocks from the northern Prince Charles Mountains, East Antarctica, have been characterised geochemically and dated from SHRIMP zircon geochronological data. Around 980 Ma ago, voluminous magmas representing a combination of mantle-derived and intracrustal melts, including orthopyroxene-quartz monzonite ('charnockite') on Loewe Massif and granitic and syenitic intrusions on Mount Collins, were emplaced during a regional high-grade tectonothermal event. Garnet leucogneiss sheets on Mount McCarthy, the products of local partial melting, were also emplaced at about this time. The geology of Fisher Massif is exceptional in that a ca 1280-Ma metavolcanic sequence and coeval granodiorite have been metamorphosed only to to the lower amphibolite facies, and intruded by a ca 1020-Ma biotite granite. None of the analysed samples shows in its isotopic systematics the effects of 500-Ma events prominent elsewhere in East Antarctica.
The following major structural types are created by the Precambrian tectonic environments of the Antarctic shield: 1) Archean protocratonic blocks; 2) Proterozoic Wegener-Mawson mobile belt; and 3) Late Proterozoic sedimentary-volcanogenic protoaulacogens. Each type reflects successive stages of evolution of the Antarctic shield in the Precambrian. Protocratonic blocks were formed between 3900 and 2700 Ma, when the environments of the charnockite-enderbite nuclei and of the granite-greenstone terranes dominated. The Wegener-Mawson mobile belt strikes throughout East Antarctica from east to west. It was formed between 2500 and 500 Ma, when the environments of granulite-gneiss terranes dominated. A polycyclic evolution with four cycles of tectonic activity culminating at 2400, 1700, 1000 and 550 Ma is a very important feature of this mobile belt. Proterozoic protoaulacogens were formed between 1200 and 500 Ma. Their formation marked the transition to the rift stage evolution of the Antarctic shield. This kind of structural interpretation of the Antarctic shield allows a more accurate definition of the position of Antarctica within Gondwana. -from Author
The Lambert Glacier graben extends S from the coast for almost 700km, and the amplitude of bedrock relief across the graben is as high as 3000-3500m. Magnetic data, however, reveal bedrock depressions 5km or more in depth, filled with nonmagnetic rocks. The rift zone is sharply discordant relative to structural grain in the older rocks, mainly lower Precambrian complexes. Deep seismic-sounding results indicate deep faults bounding the rift graben. Beneath the graben, crustal thickness is as low as 22- 24km, while on both sides of the graben, the crust is 30-34km thick. The beginning of rifting is provisionally dated as late Mesozoic, and it was probably associated with extensive crustal upwarping. Available evidence indicates a decrease in age of tectonic activity in a W direction. The W side of the rift seems more heterogeneous than the E side, which may indicate that the rift zone inherited some ancient major lineament in the crust, perhaps as old as late Archean.- Authors
Stratigraphic and structural data support the existence of a thick and extensive low-grade sedimentary cover sequence of relatively young age at Cumpston Massif and Mount Rubin compared with the underlying Archaean-Palaeoproterozic basement rocks of the southern Prince Charles Mountains. The stratigraphy of these sequences suggests sediment deposition was within a shallowing-up marine basin. Folding within the basin displays a simple structural style in comparison to older, multiply deformed rocks in the adjacent nunataks such as Mount Stinear and Mount Ruker. D1 folding and fabric development within the basin has formed in response to a northeast-southwest shortening. This stress regime may be responsible for late stage mylonite zones, thrust faults and transposed fabrics that overprint earlier structures in the basement that represent the basin margins. At Cumpston Massif, the base of the basin sediments is incorporated into a 100 m wide low-angle shear zone, with the meta-sediments ramping over deformed felsic gneiss. Similar relationships at Mount Maguire suggesting continuation of the basin further south, yet absent at Mount Rubin, creating uncertainties in extrapolating basin margins to the west. Early deformation within basement sequences prior to basin deposition suggests at least two phases of non-coaxial deformation, preserved in the folded banded iron formations at Mount Ruker. Such structures are partially obscured at Mount Stinear due to mylonitisation, and possible exhumation of the underlying crystalline basement.
Precambrian cratonic pelites from the Kaapvaal Craton in southern Africa have similar REE patterns with relative LREE enrichment and absence of significant depletion in HREEs. They have a narrow range of ratios with a mean value of 0.118, which is identical to the mean value of ≈450 worldwide fine-grained samples of all ages obtained by isotopic dilution analyses. This value is probably the best estimate for the upper continental crust. The Kaapvaal pelites also have distinct Cr/Th ratios, but overlap in Eu/Eu∗ ratios, suggesting that variable provenance and sedimentary recycling were important both during and after the Archean. Because the light REE budget is controlled chiefly by granitoids, which mask contributions of mafic-ultramafic components, the relatively uniform Sm/Nd ratios in sediments do not indicate a near-constant composition for the upper continental crust.Most Kaapvaal pelites have negative ϵNd(T) values, indicating important contributions of older crustal sources. Overall, there is a slight decrease of ϵNd(T) values with decreasing age, but no clear distinction is apparent at the A/P boundary at 2.5 Ga. Almost all of Kaapvaal pelites have TDM ages greater than their depositional ages but younger than 3.6 Ga, suggesting an absence of rocks older than 3.6 Ga in the Kaapvaal Craton.The debate on growth or no-growth of continents depends much on the choice of parameters in model calculations. The crucial parameters include sediment flux in subduction zones and delaminated lower crust, and the Sm/Nd ratio of continental crust. Unfortunately, the available data are ambiguous in modelling studies. Neodymium isotopic data and Sm/Nd ratios cannot be taken as a robust argument against the no-continental-growth model advocated by R. L. Armstrong (1991).
Interpretations of the existing magnetic data in the Lambert region raise questions about the nature of the southern Lambert Rift system. Preliminary interpretations of this data have allowed distinction of major geological blocks and magnetic trends, which can be correlated with the known geology of the Southern Prince Charles Mountains (PCMs). The objective of this investigation was to extend the magnetic data to the south and also acquire ice penetrating radar and gravity data to assist in understanding the Lambert / Amery rift system. This will provide a better understanding of the formation and breakup of Gondwana. Ice radar data will also contribute to ice mass balance analysis of this major ice drainage area in Antarctica. This research presents the methodology, data and preliminary interpretations of the airborne data acquired as part of the Prince Charles Mountains Expedition of Germany and Australia 2002/03 (PCMEGA). The area of study covered part of the southern PCMs and the adjacent polar ice cap, from approximately 72.5 to 77.5 South and 62 to 72 East. Within a month of field work more than 20000 km of survey lines at 5km line spacing and 25 km tie-line spacing was acquired over an area of approximately 81000 square kilometers. Transit flights between the base camp at Mt. Cresswell and the survey grid were utilized to collect ice radar data over the major ice tributaries feeding the Lambert Glacier. Increasing surface elevation towards the southern region of the survey grid made it necessary to divide the survey into three separate flying elevations of 2160 m, 2760 m and 3360 m (GPS height). The aeromagnetic image is characterized by long wavelength magnetic anomalies which display different trends. The southern region of the image is dominated by alternating high-low northeast-trending magnetic anomalies. These anomalies have been truncated by a northwest trending feature suggesting separation of major blocks by crustal scale faults / shear zones. The gravity data presented here is simply free-air gravity. The gravity image displays long wavelength anomalies which are contrasted by sharp gradients. North to north-north-east trending features are truncated in the northern region of the grid by a north-west trending gravitational low. The high gravitational response in the south-east region of the grid is interpreted as the `foothills' of the Gamburtsev Mountains. Detailed maps of sub-ice topography were produced that allow a 3-dimensional ice thickness correction of the gravity data and the production of crustal thickness maps. The PCMEGA airborne survey provided new elevation and ice thickness data of the upper Lambert glacier basin extending to 78 South. This data can be used to assess the state of balance by computed balance fluxes based on an improved DEM and fluxes derived from ice thickness and velocity. Maps illustrating the sub-ice topography are one of the major results of the PCMEGA project and the basis for a range of geological and glaciological interpretations.
Southwestern Australia has a long dynamic Precambrian history of crustal fragmentation and aggregation by continental collision and accretion. This interpretation contrasts with the widely held belief that most of Australia was part of a Proterozoic supercontinent in which all tectonic, magmatic, and metamorphic activity was intracontinental. The Pilbara and Yilgarn cratons are two quite different fragments of Archean continental crust that collided to form the Capricorn orogen between 2000 and 1600 Ma. The Albany-Fraser orogen formed along the southern margin of the Yilgarn craton during another major continental collision at 1300 to 1100 Ma. Rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 Ma. Subsequent continental collision along this rifted margin formed the Paterson orogen at 700 to 600 Ma. Therefore, the assembly of this considerable part of Gondwana may not have been completed until about 600 Ma.
Ar-40/Ar-39 systematics within metasedimentary rocks exposed in the southern Prince Charles Mountains, East Antarctica, were thermally reset during a period of Early Palaeozoic (between 524 +/- 1 Ma and 486 +/- 2 Ma) orogenesis. This event affected three temporally distinct (Archaean to Neoproterozoic) stratigraphic levels that are now exposed in the upper crust. In the structural record, evidence of orogenesis during Early Palaeozoic times is preserved as late-stage, subvertical mylonite zones in the Archaean orthogneiss-metasedimentary basement and thin-skinned folding and thrusting of the overlying Neoproterozoic metasedimentary rocks. Synchronous cooling ages, contrasting structural styles and similar peak metamorphic conditions are interpreted as reflecting basement-involved thin-skinned deformation that was the result of inversion of a Neoproterozoic basin. The presence of pre-existing crustal heterogeneities is the mechanism that localized Early Palaeozoic orogenesis within the region. This interpretation differs from previous models that attribute Early Palaeozoic orogenesis within the southern Prince Charles Mountains to a collisional tectonic setting. An Early Palaeozoic intra-cratonic setting for the region suggests that amalgamation between India and Antarctica was likely to have occurred prior to the final construction of Gondwana.
New U-Pb SHRIMP ages from East Antarctica point to the existence of a laterally continuous orogenic belt that bisects the East Antarctic craton. This orogenic belt juxtaposes Archean crust to the south and east against Neoproterozoic metamorphic rocks to the north and west. It defines the margin of a separate lithospheric block that consists of a large section of East Antarctica and India that did not form part of east Gondwana or Rodinia as they are currently reconstructed. Instead, this Indo-Antarctic continent accreted with west Gondwana along the Mozambique suture shortly before collision and suturing along a second "Pan-African" suture now cropping out in the southern Prince Charles Mountains and Prydz Bay regions of Antarctica. This scenario is consistent with (1) the abrupt termination of ca. 990-900 Ma tectonism recognized in the northern Prince Charles Mountains-Rayner Complex-Eastern Ghats against Paleozoic orogenic belts, (2) the lack of terranes of equivalent age found elsewhere in either Antarctica or other previously adjacent continents, and (3) the distinct detrital-zircon populations obtained from either side of this proposed suture.
New isotopic (Sm–Nd) and geochemical data are presented for volcano-sedimentary and granitic lithotypes of the Tulawaka East gold deposit in the Late Archean Sukumaland Greenstone Belt of the Tanzanian Craton. The data help to characterize the geological environment of the greenstone belt/gold deposit and the crustal evolution of the Tanzanian Shield. The volcano-sedimentary units were intruded by leucogranites and aplitic dykes that were deformed and metamorphosed to amphibolite facies grades. The Au mineralization occurs in thrust faults at the contact between the aplite dykes and the volcano-sedimentary units. The metavolcanic rocks are largely basaltic to intermediate in composition with negative Nb anomalies and flat rare earth element (REE) profiles varying from 10 to 100× chondritic values. Initial ɛNd 2.8Ga values vary from +0.9 to +5.3 and Nd model ages (Tdm) range from 2.8 to 3.0Ga. The metasedimentary rocks are generally enriched in light REE (100× chondrite) with weak negative Eu anomalies and ɛNd 2.8Ga values vary from 0.0 to +2.6. The leucogranites are garnet-rich and peraluminous with strong negative anomalies in Eu and Ti and with flat REE profiles (10–100× chondrite). The aplite dyke is also peraluminous with similar negative Eu and Ti anomalies and a flat light REE, but is depleted in heavy REE. The similarity in composition with the leucogranite suggests that the two are cogenetic and formed by fractionation of a more mafic parental magma. The combination of the flat REE element patterns and negative Nb anomalies among the mafic volcanic rocks suggests formation as an immature (island?) arc at ca. 2.8Ga. However, Nd isotope signatures in the metasedimentary rocks provide evidence of an older crustal sedimentary provenance (ca. 3.0–3.1Ga) and proximity of a continental influence. The age of the leucogranite and aplite dyke are constrained by a Sm–Nd garnet-whole-rock age of ca. 2.5Ga, indicating that the shear zone-hosted gold mineralization is younger than 2.5Ga. The range of isotopic compositions found in the Tanzanian Shield overlap with those of the Zimbabwe Craton to the south.
Laser ablation inductively coupled mass spectrometry (LA-ICPMS) dating of detrital zircon has been employed to tighten geochronological constraints from the southern Prince Charles Mountains, East Antarctica. The grains of detrital zircon are from extensive metasedimentary units that define different stratigraphic levels. Provenance information from this study has identified three lithostratigraphic units that range in age from Archaean to Neoproterozoic times. The newly defined Tingey Complex contains the oldest known strata, and consists of an Archaean felsic basement overlain by three stratigraphic layers, distinguished by ca. 3200 Ma, ca. 2800 Ma and ca. 2500 Ma detrital zircon grains. The Lambert Complex consists of a metasedimentary package, characterised by ca. 2100 Ma, ca. 1900–1800 Ma and ca. 2600 Ma detrital zircon grains that possibly overlies late Palaeoproterozoic orthogneiss. The Neoproterozoic Sodruzhestvo Group comprises the youngest exposed unit and consists of a thick, clastic-dominated sequence that is distinguished by ca. 1170–970 Ma grains. This study suggests that the isotopic differences reported from the southern Prince Charles Mountains are a result of stratigraphic stacking, rather than due to juxtaposition via collision and accretion tectonics. The discovery of ca. 2500 Ma detrital zircon grains within the Palaeoproterozoic metasedimentary rocks of the Tingey Complex strengthens correlations with Archaean fragments exposed in neighbouring regions of East Antarctica. Constraining the deposition of the Sodruzhestvo Group to the mid-Neoproterozoic period suggests a prominent period of basin development occurred within the southern Prince Charles Mountains at this time.
The Capricorn Orogen in central Western Australia records the Palaeoproterozoic collision of the Archaean Pilbara and Yilgarn Cratons. Until recently only one orogenic event was thought to be the cause of this collision, the 1830–1780Ma Capricorn Orogeny. However, recent work has uncovered an older event, the Glenburgh Orogeny that occurred between 2000 and 1960Ma. The Glenburgh Orogeny reflects the collision of a late Archaean to Palaeoproterozoic microcontinent (the Glenburgh Terrane) with the Archaean Yilgarn Craton and is therefore tectonically distinct as well as significantly older than the widespread 1900–1800Ma tectonothermal events recorded in northern Australia.The Glenburgh Terrane preserves a different history from either the Yilgarn or Pilbara Cratons. Granitic gneiss protoliths dated at ca. 2550Ma were intruded by widespread granite magmatism dated at 2005–1970Ma, accompanied by high-grade metamorphism and deformation throughout the terrane. At ca. 1960Ma silicic granite of the Bertibubba Supersuite intruded the northern margin of the Yilgarn Craton along the Errabiddy Shear Zone, a crustal-scale shear zone that today marks the contact of the Glenburgh Terrane and Yilgarn Craton. At ca. 1950Ma silicic dykes intruded the southernmost part of the Glenburgh Terrane, marking the end of the Glenburgh Orogeny. East of the Glenburgh Terrane the Glenburgh Orogeny resulted in the cessation of mafic volcanism in the Bryah Basin, and the basin’s eventual closure. Siliciclastic, carbonate and chemical sedimentary rocks were deposited in the Padbury Basin that formed a retro-arc foreland basin on top of the Bryah Basin, and probably records the later stages of the Glenburgh Orogeny collision.
Ion microprobe dating of structurally constrained felsic intrusives indicate that the rocks of the northern Prince Charles Mountains (nPCMs) were deformed during a single, long-lived Neoproterozoic tectonic event. Deformation evolved through four progressively more discrete phases in response to continuous north–south directed compression. In the study area (Radok Lake), voluminous granite intrusion occurred at ∼990 Ma, contemporaneous with regionally extensive magmatism, peak metamorphism, and sub-horizontal shearing and recumbent folding. Subsequent upright folding and shear zone development occurred at ∼940 Ma, while new zircon growth at ∼900 Ma constrains a final phase of deformation that was accommodated along low-angle mylonites and pseudotachylites. This final period of deformation was responsible for the allochthonous emplacement of granulites over mid-amphibolite facies rocks in the nPCMs. The age constraints placed on the timing of deformation by this study preclude the high-grade reworking of the nPCMs as is postulated in some of the recent literature. Furthermore, 990–900 Ma orogenesis in the nPCMs is at least 50 Myr younger than that recognised in other previously correlated Grenville aged orogenic belts found in Australia, east Africa and other parts of the Antarctic. This distinct age difference implies that these belts are probably not correlatable, as has been previously suggested in reconstructions of the supercontinent Rodinia.
Geochemical and Sm-Nd isotopic data are presented on the sediments and their potential source rocks from the Late Proterozoic-Cambrian Adelaide Fold Belt in southern Australia. The data indicate that the Archean to Mid-Proterozoic basement rocks of the Gawler Craton in southern Australia record a history of additions from the contemporary depleted mantle, some of which assimilated preexisting crust. The chemical and isotopic data are consistent with a mode in which deformation and subsequent rapid exhumation during the Delamerian Orogeny provided the source for the thick Ordovician-Silurian flysch in the Lachlan Fold Belt to the east. While the data indicate a model of regional, intracontinental additions via advection of mantle melts accompanied by assimilation of preexisting crustal materials, they do not support a model of purely intracrustal recycling.
Derivation of Phanerozoic zircon 206Pb/238U ages by SHRIMP depends on calibration against an independently dated standard. The qualities of four different zircon standards (SL13, QGNG, AS3 and TEMORA 1) are assessed herein. Not all of these behave consistently on SHRIMP with respect to their ages as determined by IDTIMS. SL13, the most commonly used standard over the past decade and a half, is the most heterogeneous in Pb/U. In addition, when SL13 is used as the calibration standard, the varied ages resulting from that heterogeneity are generally younger than ages derived from the other three standards. AS3-calibrated ages are the oldest of the group. Only QGNG and TEMORA 1, when calibrated relative to each other, yield ages on SHRIMP that are consistent with their IDTIMS ages. Of these two, TEMORA 1 has the distinct advantage of producing consistent IDTIMS ages at high precision. Because of these factors and its availability, we recommend its use in geological studies where precise and accurate Pb/U zircon ages are imperative. Approximate conversion factors have been derived to improve quantitative inter-comparison between SHRIMP ages that have been calibrated against the different standards. These refinements significantly advance the role that SHRIMP can play in the numerical calibration of the Phanerozoic timescale.
U–Pb ion microprobe analysis of zircon indicates that the oldest rocks from the southern Prince Charles Mountains, east Antarctica, consist of granitoid rocks of the Mawson Suite that were emplaced between 3185 and 3155Ma. These granitoids are tectonically intercalated with the Menzies Series, a thick sequence of Cr-quartzite, marble, metaconglomerate and kyanite-bearing metapelite. Together these rocks were deformed during a single Late Archaean tectonothermal event that occurred between 2790 and 2770Ma based on the ages of two syn-tectonic leucosomes. This event deformed the terrane via south to southwest-directed shortening and metamorphosed the rocks to upper-amphibolite facies. A sample of post-tectonic pegmatite with an age of 2645Ma further confirms the Archaean age of deformation and metamorphism recorded by these rocks. These new age constraints demonstrate that: (1) the sialic basement (Mawson Suite+Menzies Series) of the southern Prince Charles Mountains formed entirely in the Archaean and, (2) these rocks do not share a common geologic history with the other known exposures of pre-Gondwana basement from the East Antarctic Craton, nor with the rocks of the previously continuous Gawler Craton of southern Australia. This latter point implies that the East Antarctic Craton probably did not exist as a single entity in the Archaean and Early Proterozoic, but rather formed in the Middle to Late Proterozoic via the amalgamation of a number of discrete lithospheric blocks.
The marginal part of the East Antarctic Craton, the northern Prince Charles Mountains included, is traditionally thought to be a fragment of the extended Late Proterozoic (1300‐900 Ma) orogenic belt. Its initiation and development is synchronous with the formation of some metamorphic belts in India, eastern Africa, and Australia. These belts were considered to represent a primary accretionary system, development of which resulted in the formation of East Gondwana during the growth and consolidation of Rodinia [1]. Subsequent isotopic studies in East Antarctica revealed the relatively intense development of Paleozoic tectonothermal processes in the latter [2]. This allowed the inference that East Gondwana is presumably a collage of continental blocks that were amalgamated only in the Paleozoic [3]. Granulite‐gneisses developed in the northern part of the Prince Charles Mountains have served as the object of numerous studies. Some researchers [4] conclude that the degree of thermal reworking in the Paleozoic in this region was insignificant. Based on study of metamorphism and Sm‐Nd data, others assume at least two tectonothermal events that reworked its rocks approximately 800 and 630‐500 Ma ago [5]. This contradiction cannot be overcome unless the conditions and age of magmatism and metamorphism are reconstructed. In this work, we present the results of isotopic dating of metamorphic rocks from the Radok Lake area in the northern part of the Prince Charles Mountains. The northern Prince Charles Mountains are formed by ridges and mountainous massifs separated by outlet glaciers. These mountainous structures are located in the southeastern wall of the large Emery shelf glacier. Granulite rocks constitute mountainous massifs, which were subdivided previously into the sedimentary Larsemann and largely igneous Reinbolt groups. The Reinbolt Group unites pyroxene plagiogneisses and charnockite gneisses, which enclose small slices and bodies of amphibole‐pyroxene‐plagioclase crystalline schists and subordinate biotite‐garnet gneisses. The largest massifs of slightly deformed porphyry-like charnockites associate spatially with the rocks of this group. The Larsemann Group is represented by migmatized biotite‐ garnet gneisses with cordierite and sillimanite, plagiogneisses, and crystalline schists. They enclose subordinate stratiform and lenticular bodies of charnockite‐gneisses, amphibole‐pyroxene‐plagioclase schists, amphibolites, and quartzites. The rocks of the Reinbolt Group usually form dome-shaped structures, which are enveloped by migmatized and intensely deformed rocks of the Larsemann Group. In the Radok Lake area, Permian‐Triassic slightly deformed coaliferous sedimentary sequences and Cenozoic moraine cover are outcropping. The structural‐tectonic relationships between these groups remain unclear thus far. This is explained by their occurrence in the form of fragmentary outcrops and development of metamorphic processes, which mask the primary relationship of the rocks. For example, charnockitoids and garnet‐biotite gneisses of the Larsemann Group grade frequently into each other, while garnet‐biotite gneisses demonstrate relicts of substrate rocks (charnockitoids). All these features may indicate that some garnet‐biotite gneisses may have originated from enderbite‐charnockite rocks during their granitization. At the same time, hypersthene plagiogneisses‐enderbites and pyroxene schists of the Reinbolt Group enclose lenses of plagioclases (labradorites), while charnockitoids contain shadow structures formed by relicts of pyroxene schists. This points as well to the long formation history of the rocks constituting this group.
The East Antarctic Shield consists of a variety of Archaean and Proterozoic-Cambrian high-grade terranes that have distinct crustal histories and were amalgamated at various times in the Precambrian-Cambrian. High-grade Pan-African tectonism at 600-500 Ma is recognized from four distinct belts: the Dronning Maud Land, Lützow-Holm Bay, Prydz Bay and Denman Glacier Belts. These high-grade belts juxtapose distinct Mesoproterozoic and Neoproterozoic crustal provinces (Maud, Rayner and Wilkes), the Rauer Terrane, and have also marginally affected Archaean cratonic remnants in the Napier Complex and southern Prince Charles Mountains. The Wilkes Province experienced its principal tectonothermal events prior to 1130 Ma and was not affected by the younger events that characterize the Maud Province (1150 and 1030-990 Ma), the Rayner Province (990-920 Ma) and the Rauer Terrane (1030-990 Ma). These differences between the isotopic/event records of the basement provinces now separated by the Pan-African belts require that the older provinces were not formerly parts of a continuous 'Grenville' belt as proposed in the SW US-East Antartic model. East Antartica was not a single unified crustal block within either East Gondwana or Rodinia until the Cambrian, which is now demonstrated to be the key phase of high-grade and ultrahigh-temperature (UHT) metamorphism associated with supercontinent assembly. The high-grade Pan-African tectonism is characterized by extensive infracrustal melting, clockwise P-T paths, rapid post-peak exhumation along isothermal decompression paths to shallow-or mid-crustal levels by 500 Ma and the generation, at least locally, of UHT conditions. A significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects. Whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust, these one-dimensional models are inconsistent with present crustal thicknesses of 25-35 km in the Pan-African domains of the East Antarctic Shield.
Metapelitic rock samples from the NE Shackleton Range, Antarctica, include garnet with contrasting zonation patterns and two age spectra. Garnet porphyroblasts in K-rich kyanite-sillimanite-staurolite-garnet-muscovite-biotite schists from Lord Nunatak show prograde growth zonation, and give Sm-Nd garnet, U-Pb monazite and Rb-Sr muscovite ages of 518 ± 5, 514 ± 1 and 499 ± 12 Ma, respectively. Geothermobarometry and P-T pseudosection calculations in the model system to 650°C/7.5 kbar, and partial resorption during a subsequent P-T decrease to <650°C at <6 kbar. All data indicate that rocks from Lord Nunatak were affected by a single orogenic cycle. In contrast, garnet porphyroblasts in K-poor kyanite-sillimanite-staurolite-garnet-cordierite-biotite-schists from Meade Nunatak show two growth stages and diffusion-controlled zonation. Two distinct age groups were obtained. Laser ablation plasma ionization multicollector mass spectrometry in situ analyses of monazite, completely enclosed by a first garnet generation, yield ages of c. 1700 Ma, whereas monazite grains in open garnet fractures and in most matrix domains give c. 500 Ma. Both age groups are also obtained by U-Pb thermal ionization mass spectrometry analyses of matrix monazite and zircon, which fall on a discordia with lower and upper intercepts at 502 ± 1 and 1686 ± 2 Ma, respectively. Sm-Nd garnet dating yields an age of 1571 ± 40 Ma and Rb-Sr biotite analyses give an age of 504 ± 1 Ma. Integrated geochronological and petrological data provide evidence that rocks from Meade Nunatak underwent a polymetamorphic Barrovian-type metamorphism: (1) garnet 1 growth and subsequent diffusive garnet annealing between 1700 and 1570 Ma; (2) garnet 2 growth during the Ross Orogeny at c. 500 Ma. During the final orogenic event the rocks experienced peak P-T conditions of about 650°C/7.0 kbar and a retrograde stage at c. 575°C/4.0 kbar.
The West Australian Craton and its adjacent orogens have a Precambrian history of repeated generation, dispersal, and aggregation of continental crust. They indicate the mobility of rafts of Precambrian continental crust and the operation of plate tectonic processes that were at least as active as those of the present. Major episodes of continental rifting and of collision and aggregation of crustal fragments are recorded. These episodes of continental aggregation coincide with similar activity seen in other Precambrian crust around the Earth. They may reflect the formation of Precambrian supercontinents. -from Author
Three Precambrian basement provinces extend from the southern coast of Australia into East Antarctica when reconstructed in a Gondwana configuration. These are, from east to west, the Mawson Craton, and the Albany-Fraser and Pinjarra Orogens. The Mawson Craton preserves evidence for tectonic activity from the late Archaean until the earliest Mesoproterozoic. It is exposed in the Gawler Craton of South Australia, the Terre Adelie and King George V Land coastline of East Antarctica, and the Miller Range of the central Transantarctic Mountains. It may form a significant part of the ice-covered East Antarctic Shield, although insufficient data are available to constrain its lateral extent. The Mawson Craton underwent late Palaeoproterozoic tectonism along its eastern margin (the Kimban Orogeny) and the occurrence of c. 1700 Ma eclogites in the Transantarctic Mountains implies that this was, in part, a collisional event, although elsewhere it was characterized by low P/T metamorphism. The western margin of the Mawson Craton collided with a continental fragment comprising the Nawa Domain of the Gawler Craton, the Coompana Block and the Nornalup Complex of Western Australia at c. 1560 Ma during the Kararan Orogeny. The western edge of the Nornalup Complex later collided with the Biranup and Fraser Complexes and Yilgarn Craton to form the Albany-Fraser Orogen during two stages of tectonism at c. 1350-1260 and 1210-1140 Ma. The Pinjarra Orogen truncates the western margin of the Yilgarn Craton and Albany-Fraser Orogen, and contains allochthonous 1100-1000 Ma gneissic blocks transported along the craton margin during at least two stages of Neoproterozoic transcurrent movement. It divides East Gondwana into Australo-Antarctic and Indo-Antarctic domains, which are distinct continental fragments with different Proterozoic histories that were juxtaposed by oblique collision at 550-500 Ma during the assembly of Gondwana. The path taken by the Pinjarra Orogen beneath the Antarctic ice sheet is unknown, but it is of similar width and length to the East African Orogen, and must have been a fundamental Neoproterozoic boundary of critical importance to supercontinent assembly and breakup.
The basement in the Pointe Geologie Archipelago, around the French Dumont d'Urville station in Terre Adelie, comprises a metapelitic migmatitic complex with a 1.7 Ga metamorphic evolution differing from that generally found in other areas of the East Antarctic Shield. In Terre Adelie, although the oldest crustal precursors (Nd T (sub DM) model ages) are ca. 2.2-2.4 Ga old, inherited zircon SHRIMP ages are ca. 1.73-1.76, 2.6 and 2.8 Ga. The migmatitic evolution is restricted to a single event which is dated at 1.69 Ga by newly formed zircons (SHRIMP) and by U-Pb and (super 207) Pb/ (super 206) Pb evaporation TIMS ages of monazite. When interpreted as cooling ages, Sm-Nd garnet (1.60 Ga) and Rb-Sr micas (1.50 Ga) ages would be indicative of a slow cooling rate, suggestive of a long-lived major thermal anomaly. Geological processes such as sediment deposition, HT-LP metamorphism and anatexis and coeval intrusion of mafic magmas occurred during a very short time. This suggests that the migmatite complex is related to a major lithospheric thinning associated with a thermal anomaly coeval with syn-metamorphic mafic magmatism. Such thinning may have developed in a 2.8/2.4 Ga old basement, comparable with the Port Martin formations located 50 km further east. In the Gawler Craton (South Australia) similar units are found which could have formed, together with the Terre Adelie basement, as a single shield by a collage of various terrains that existed prior to ca. 1.5 to 1.6 Ga ago, comprising the tt" Mawson Continenttt" .
New Sm–Nd isotopic measurements made on granulite-facies metamorphic rocks from East Antarctica provide firm evidence that crust of ~3,500-Myr age exists in the Fyfe Hills. Zircon U–Pb data provide further documentation for a granulite-facies event 2,500 Myr ago, during which Rb, U, Sm and Nd were highly mobile. The U–Pb and Rb–Sr isotopic systems were seriously disrupted and in most samples give meaningless model ages. In contrast, Sm–Nd model ages were offset only slightly. A large time interval of 1,000 Myr between the times of crust formation and granulite-facies metamorphism has not previously been reported for Archaean rocks, and suggests that 2,500 Myr ago the Fyfe Hills may have been located in an Andean- or Himalayan-type continental margin where crust already 1,000-Myr old was involved in an orogenic event.