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A synopsis of events related to the assembly of Eastern Gondwana
Abstract
The assembly of the eastern part of Gondwana (eastern Africa, Arabian–Nubian shield (ANS), Seychelles, India, Madagascar, Sri Lanka, East Antarctica and Australia) resulted from a complex series of orogenic events spanning the interval from ∼750 to ∼530 Ma. Although the assembly of Gondwana is generally discussed in terms of the suturing of east and west Gondwana, such a view oversimplifies the true nature of this spectacular event. A detailed examination of the geochronologic database from key cratonic elements in eastern Gondwana suggests a multiphase assembly. The model outlined in this paper precludes the notion of a united east Gondwana and strongly suggests that its assembly paralleled the final assembly of greater Gondwana. It is possible to identify at least two main periods of orogenesis within eastern Gondwana. The older orogen resulted from the amalgamation of arc terranes in the Arabian–Nubian shield region and oblique continent–continent collision between eastern Africa (Kenya–Tanzania and points northward) with an, as of yet, ill-defined collage of continental blocks including parts of Madagascar, Sri Lanka, Seychelles, India and East Antarctica during the interval from ∼750 to 620 Ma. This is referred to as the East Africa Orogen (EAO) in keeping with both the terminology and the focus of the paper by Stern [Annu. Rev. Earth Planet. Sci. 22 (1994) 319]. The second major episode of orogenesis took place between 570 and 530 Ma and resulted from the oblique collision between Australia plus an unknown portion of East Antarctica with the elements previously assembled during the East African Orogen. This episode is referred to as the Kuunga Orogeny following the suggestion of Meert et al. [Precambrian Res. 74 (1995) 225]. Paleomagnetic data are currently too few to provide a rigorous test of this proposal, but the extant data do not conflict with the notion of a polyphase assembly of eastern Gondwana. The major conclusion of this paper is that east Gondwana did not exist until its Cambrian assembly.
... In many cases, IBC has been shown to occur during the retrograde stage of counter-clockwise P-T paths (Harley 1989;Bohlen 1991), but hybrid P-T paths showing early ITD and late IBC have also been reported (e.g., White et al. 2002;Baba et al. 2019). In general, many metamorphic terranes show evidence of ITD, which is considered to reflect the rapid exhumation of lower crustal rocks due to orogenic collapse or isostatic rebound of over-thickened crust formed by collisional orogeny South India, andMadagascar (e.g., Shiraishi et al. 1994, 2008;Meert 2003;Boger et al. 2015;Osanai et al. 2016;Durgalakshmi et al. 2021). Detailed metamorphic studies of the LHC have been conducted at several exposures along the Sôya Coast ( Fig. 1b; e.g., Rundvågshetta: Kawasaki et al. 2011, Hiroi et al. 2019Skallevikshallsen: Kawakami et al. 2016), revealing peak P-T conditions of 13-15 kbar and ~ 1040 °C, and that ITD cooling was involved with the interaction of a Cl-rich fluid (Kawakami et al. 2016) and the supercooling of melt inclusions (Hiroi et al. 2019). ...
... The LHC, an Ediacaran to Cambrian orogenic belt, occupies a vast area of about 500 km between the Western Rayner Complex (WRC) and the Yamato Mountains in East Antarctica ( Fig. 1a and b; Shiraishi et al. 1994;. Many studies have referred to the LHC as a 600-500 Ma continent collisional belt that also extends through Sri Lanka, South India, and Madagascar (e.g., Shiraishi et al. 1994Shiraishi et al. , 2008Meert 2003;Boger et al. 2015;Osanai et al. 2016). ...
... The Lützow-Holm Complex (LHC) is situated adjacent to the East African-Antarctic Orogen (EAAO). Key sutures and orogenic belts are taken from Fitzsimons (2000) and Meert (2003) Dunkley et al. (2020). Main tectonic boundary in the Sør Rondane Mountains is taken from and Osanai et al. (2013). ...
This paper reports the metamorphic texture of cordierite megacrysts and the metamorphic P–T path of a newly exposed section of gneiss in East Antarctica. We used mineral textures and pseudosection modeling to reconstruct the metamorphic P–T path of cordierite- and spinel–garnet-bearing gneisses from Botnnuten, an isolated nunatak located ~ 60 km from the southern edge of Lützow-Holm Bay in East Antarctica. The gneisses underwent low-P granulite-facies metamorphism at 5.0–6.1 kbar and 850 ± 20 °C followed by isobaric cooling. The isobaric cooling path implies long residence in the middle to shallow crustal level without rapid exhumation. This contrasts with the widely recognized clockwise P–T path of basement rocks of the Lützow-Holm Complex. The rocks at Botnnuten have long been considered part of the Lützow-Holm Complex based on their petrographical features and geothermobarometric data. However, the present results, combined with a reevaluation of available data, indicate the metamorphic history of the Botnnuten gneisses is more comparable to that of the Yamato Mountains, located southwest of the study area.
... The assembly of the Gondwana supercontinent was mainly governed by continent-continent collision, high-grade metamorphism, crustal anatexis and post-collisional magmatism, leading to the development of various Pan-African orogenic belts (Fitzsimons, 2003;Meert, 2003;Collins and Pisarevsky, 2005;Santosh et al., 2017;Boger et al., 2019;Mulder et al., 2019). The formation of Gondwana assembly is associated with two orogenic belts -the East African orogen and the Kuunga orogen. ...
... The N-S striking East African orogen ($750-620 Ma) is formed due to the closure of Mozambique Ocean, resulting in the collision between Sahara-Kalahari-Congo crustal block to the west and India-Western Australia-East Antarctica to the east (Stern, 1994;Fritz et al., 2013). However, oceans still existed between southern and eastern India, Congo Craton, Kalahari Craton, Western Australia and East Antarctica, which were subsequently closed by $ 500 Ma (e.g., Meert, 2003;Collins and Pisarevsky, 2005). This ocean closure led to the development of the Kuunga orogen ($635-488 Ma), marking the youngest orogenic event in the Gondwana assembly ( Fig. 1a; Meert, 2003). ...
... However, oceans still existed between southern and eastern India, Congo Craton, Kalahari Craton, Western Australia and East Antarctica, which were subsequently closed by $ 500 Ma (e.g., Meert, 2003;Collins and Pisarevsky, 2005). This ocean closure led to the development of the Kuunga orogen ($635-488 Ma), marking the youngest orogenic event in the Gondwana assembly ( Fig. 1a; Meert, 2003). This orogeny has resulted in high-grade metamorphism along the margins of Congo and Kalahari cratons (557-555 Ma; 650-875°C at 6.7-11.0 ...
... In the early Neoproterozoic, three prominent oceans existed in the world: the Mirovoi Ocean (Meert and Lieberman, 2008), the Mawson Sea (Meert, 2003;Meert and Lieberman, 2008), and the Mozambique Ocean (Collins et al., 2003;Collins and Pisarevsky, 2005). Among them, the Mozambique Ocean was considered as a Pacific-sized ocean, and to have existed mainly between India and Arabia-Africa (Li et al., 1995(Li et al., , 2008Milton et al., 2017;Liao et al., 2018;Merdith et al., 2017;Mole et al., 2018;Hu et al., 2022). ...
... Among them, the Mozambique Ocean was considered as a Pacific-sized ocean, and to have existed mainly between India and Arabia-Africa (Li et al., 1995(Li et al., , 2008Milton et al., 2017;Liao et al., 2018;Merdith et al., 2017;Mole et al., 2018;Hu et al., 2022). Its evolution, from north to south, is primarily recorded in the rock strata of Turkey, the Levant, Arabia, Oman, India, Mozambique, Madagascar, Sri Lanka, and East Antarctica (e.g., Meert, 2003;Jacobs and Thomas, 2004;Bybee et al., 2010;de Wall et al., 2012;Fritz et al., 2013;Santosh et al., 2017;Mole et al., 2018;Collins et al., 2021;Baba et al., 2022 and references therein). Recently, some scholars discovered rocks providing evidence of the Neoproterozoic oceanic crustal rocks in the central and southern parts of Tibet, suggesting that they may represent the remnants of the Mozambique Ocean (Zhang et al., 2014aHu et al., 2016Hu et al., , 2018aZeng et al., 2018a;Zhang et al., 2021;Yu et al., 2023 and references therein). ...
... The EAO is a vast orogenic belt that stretches over 6000 km on the earth, from Turkey, Arabia, and the Levant along the margins of eastern African and western Indian into East Antarctic (e.g., Meert, 2003;Jacobs and Thomas, 2004;Fritz et al., 2013;Collins et al., 2021). The northern EAO is marked by the Mozambique Ocean, which probably was a Pacific-sized ocean basin that divided the landmass of India and the Arabian-African from around 1080-600 Ma (Meert, 2003). ...
... In Kenya, Tanzania, and Mozambique, the belt is composed principally of the Eastern and Western Granulites, the Irumide Belt and the Nampula Block. The formation of the Mozambique Belt and the wider East African Orogen spans an orogenic cycle beginning with the breakup of Rodinia from ~ 850 Ma, the polyphase amalgamation of Gondwana (750 and 530 Ma), and later (≤ 530 Ma) post orogenic extension and magmatism (Stern 1994;Meert 2003;Collins and Pisarevsky 2005;Fritz et al. 2013;Fritz and Hauzenberger 2021). ...
... It is now established that the polyphase amalgamation of Gondwana led to two separate and distinct orogenic phases which are recorded in the Mozambique Belt (Stern 1994;Meert 2003;Collins and Pisarevsky 2005;Fritz et al. 2013). The earlier phase known as the "East African" (Stern 1994) or "Mozambique" Orogeny (Fritz and Hauzenberger 2021) is traditionally framed as the collision of "Eastern" and "Western" Gondwana (e.g., Stern 1994) but specifically corresponds to the collision of Azania, the Arabian-Nubian Shield and the Congo-Tanzania-Bangweulu cratons, and the closure of the Mozambique Ocean (Collins and Pisarevsky 2005;Fritz et al. 2013). ...
... India and Australia and the final assembly of Gondwana finally concluding at ~ 500 Ma (Meert 2003;Collins and Pisarevsky 2005). Records of the Kuungan Orogeny are most prominent in the Western Granulites of Tanzania and Mozambique and within the Nampula and Irumide belts, as is post orogenic extension and voluminous magmatism (Cutten et al. 2006;Johnson et al. 2006;Hauzenberger et al. 2007;Bingen et al. 2009;Thomas et al. 2010Thomas et al. , 2014. ...
The direct dating of gem-quality garnet mineralization has been extremely limited, even though it has been known for decades that garnet may be dated by the U–Pb method. Here, we demonstrate the application of in situ laser U–Pb geochronology on gem-quality tsavorite to determine the timing of mineralization from two localities in the Mozambique Belt, Tanzania.
U–Pb dating of tsavorite from Merelani and Umba provides ages of 569.5 ± 6.8 Ma and 540.0 ± 5.8 Ma, respectively. Due to the high closure temperature of the U–Pb system in garnet, we argue that these ages correspond to tsavorite mineralization. These ages postdate the East African Orogeny (650–620 Ma), the most significant metamorphic episode recorded in the Mozambique Belt, which had been previously considered to be the main tsavorite mineralization event. Instead, these dates correspond to the later Kuungan orogenic episode (570–530 Ma), associated with the final amalgamation of Gondwana. The mineralization of tsavorite tens of millions of years after the East African Orogeny in the Mozambique Belt illustrates the benefits of direct dating of gem-quality garnet to determine mineralization timing and style.
... For example, Jacobs and Thomas (2004) proposed an East African-Antarctic Orogen (EAAO; Fig. 1a), which was an extension in Antarctica of the East African Orogen (EAO) of Stern (1994), and which constitut-ed one huge orogenic belt that was active from~650 to 500 Ma. On the other hand, Meert (2003) proposed two crossing orogens, with the East African Orogen active during 750-620 Ma and the Kuunga Orogen during 580-500 Ma (Fig. 1b). Since the SRM lie within an orogen in any model, they are recognized as a key region for understanding the geological phenomena during the collisions and for testing the proposed tectonic models. ...
... Since the SRM lie within an orogen in any model, they are recognized as a key region for understanding the geological phenomena during the collisions and for testing the proposed tectonic models. The tectonic models of the SRM are still under debate, with some interpretations close to those of Jacobs and Thomas (2004) (e.g., Osanai et al., 2013), others similar to those of Meert (2003) (e.g., Grantham et al., 2013;Tsukada et al., 2017), and with no consensus so far. ...
... If such a boundary were to be found over a wide area of the SRM, the tectonics of the entire SRM could be explained by thrust nappe movements that occurred during two collisional events at~650-600 Ma and~570-550 Ma. With regard to possible tectonic models for the final stages of formation of the Gondwana supercontinent, our results support the idea of a two-stage amalgamation, as proposed by Meert (2003). ...
The Sør Rondane Mountains, East Antarctica have been thought to be situated in the collision zone between East and West Gondwana during the final stage of amalgamation of the Gondwana supercontinent. They are therefore recognized as a key region for understanding the geological phenomena during the collisions and for testing the proposed tectonic models. We identified metamorphic rocks with different pressure–temperature–time paths that are bounded by a ductile shear zone at Oyayubi ridge, Brattnipene, Sør Rondane Mountains. Based on field and microscopic observations, chemical analyses of minerals, and zircon U–Pb dating, the sillimanite–garnet–biotite gneisses (i.e., pelitic gneisses) from higher structural level show a peak metamorphism at ca. 590 Ma that took place under conditions of ca. 830–840 °C and 0.8–0.9 GPa, and these high-temperature conditions lasted until ca. 550 Ma. These rocks underwent isothermal decompression and then retrograde hydration under lower pressure–temperature conditions than 530 °C and 0.4 GPa at ca. 530 Ma. In contrast, the orthogneisses that consist of hornblende–biotite gneiss and garnet–clinopyroxene gneiss from lower structural levels did not undergo metamorphism at ca. 600 Ma, but underwent metamorphism at ca. 570 Ma and reached peak conditions of 700–760 °C and 0.6–0.9 GPa at ca. 560–550 Ma. These observations suggest thrusting of the pelitic gneiss over the orthogneiss at ca. 570–550 Ma, causing a prograde metamorphism of the orthogneisses and a decompression of the pelitic gneisses as well as uplift and subsequent rapid denudation. The results indicate two stages of collision in the Sør Rondane Mountains, and that the ductile shear zone that bounds the pelitic gneiss and orthogneiss units may have been part of the continental plate collision boundary at ca. 570–550 Ma.
... year that the assembly of Gondwana was not achieved through one orogeny along a single suture, but rather through the assembly of multiple terranes along different orogenic belts during a long-lasting period (Fig. 1a, c, and d, Collins and Pisarevsky, 2005;Fritz et al., 2013;Meert, 2003;Meert and Van Der Voo, 1997;collins et al., 2021a, 2021b. There is now a consensus that Gondwana is formed through two major orogenic events, with an earlier event usually termed as the East African Orogeny (~850 -620 Ma, from accretion to final collision) and a relatively younger event often named as the Kuunga Orogeny (~570 -530 Ma, Meert, 2003, Meert andVan Der Voo, 1997; or ~600 -500 Ma, Fritz et al., 2013; or ~570 -500 Ma with a coeval Malagasy orogeny, Collins Cawood et al., (2007), and Collins and Pisarevsky (2005). ...
... year that the assembly of Gondwana was not achieved through one orogeny along a single suture, but rather through the assembly of multiple terranes along different orogenic belts during a long-lasting period (Fig. 1a, c, and d, Collins and Pisarevsky, 2005;Fritz et al., 2013;Meert, 2003;Meert and Van Der Voo, 1997;collins et al., 2021a, 2021b. There is now a consensus that Gondwana is formed through two major orogenic events, with an earlier event usually termed as the East African Orogeny (~850 -620 Ma, from accretion to final collision) and a relatively younger event often named as the Kuunga Orogeny (~570 -530 Ma, Meert, 2003, Meert andVan Der Voo, 1997; or ~600 -500 Ma, Fritz et al., 2013; or ~570 -500 Ma with a coeval Malagasy orogeny, Collins Cawood et al., (2007), and Collins and Pisarevsky (2005). (b) is modified after Stern (1994). ...
... (c) is after Boger and Miller (2004), and Boger et al., (2001). (d) is modified after Meert (2003). and Pisarevsky, 2005), although the details of them are still topics of discussions (Fig. 1a-d, Collins and Pisarevsky, 2005;Fritz et al., 2013;Kröner, 2001;Meert, 2003;Meert and Van Der Voo, 1997;Satish-Kumar et al., 2013;Stern, 1994;Torsvik and Cocks, 2013;Veevers, 2017;Schmitt et al., 2018). ...
The reconstruction of megacontinent Gondwana was arguably the first crowning achievement of paleogeography, nonetheless the kinematics of its assembly remains controversial. The now-outmoded concept that Gondwana assembly was simply the amalgamation of East and West Gondwana has been replaced by models involving multiple terrane accretions and continental collisions along different orogenic belts. Although the affinities of large cratons are well established, figuring out the relationships between the multiple “Pan-African” orogenic belts has been hindered by poorly defined smaller intervening terranes. At the center of Gondwana, the polymetamorphic terranes in Sri Lanka have been correlated to various crustal blocks without broad consensus, mainly because of a paucity of high-quality geochronological results. Terrane correlations and figuring out the spatial distributions of “Pan-African” orogenic belts in the central part of Gondwana are, therefore, hampered by the controversies about Sri Lanka. We present new data on the high-grade metamorphic rocks occurring in the Highland Complex of Sri Lanka, which reveal the widespread Paleoproterozoic magmatism with U-Pb ages of ≥2465 – 1803 Ma and uniform Archean Hf model ages. Our data confirm the pervasive metamorphic ages of ~610 – 510 Ma, and for the first time, we present multiple episodes of metamorphism at Paleoproterozoic (1854 – 1803 Ma) and Neoproterozoic (~637 – 635 Ma) which are comparable with those reported from the East African Orogen. Based on a comparison with neighboring crustal blocks, we suggest that these early Precambrian basement components as well as the multiple metamorphism of the Highland Complex in Sri Lanka can be correlated with micro-continent Azania. These new data not only confirm the widespread early Precambrian basement components in Sri Lanka, but also open up new ways for terrane correlations from East Africa through Sri Lanka to East Antarctic.
... T he growth of megacontinent Gondwana resulted from plate reorganization following the breakup of Rodinia during the late Neoproterozoic-Cambrian interval. Gondwana assembly involved the suturing of different blocks within the East African, Brasiliano, Damara and Kuunga orogens and concomitant destruction of the Mozambique, Brasiliano, and Damaran oceans [1][2][3][4][5][6][7][8] . The East African Orogen (EAO) is a longlived (>400 Ma) accretionary-style margin at one side of the Mesoproterozoic-Neoproterozoic Mozambique Ocean, which separated India and Azania (central Madagascar, Somalia, eastern Ethiopia and Arabia) from the rest of Africa [6][7][8][9] . ...
... Azania collided with eastern parts of Africa between 640 and 600 Ma 6 . This was followed by final Gondwana amalgamation between 550 and 500 Ma [1][2][3] . The assembly of Gondwana coincides with a period of Earth's history marked by dramatic changes in atmospheric circulation, oceanic circulation, the rapid motion of continents, nucleation of the inner core, hyperactive reversing magnetic field, a decrease of geothermal gradients along subduction zones, climatic variations, steep increase in O 2 and the rise of metazoan life [10][11][12][13][14][15][16][17] . ...
... Various models that deal with the progressive assembly of Gondwana have been proposed [2][3][4][5][6]22,23 . Recently, coeval Neoproterozoic orogenic activity was identified in the Tarim craton 24 and the Lhasa Terrane hinting at possible links to orogenic events in eastern Gondwana 25 . ...
The serpentine orogenic belts that formed during the Neoproterozoic assembly of Gondwana resulted in geodynamic changes on the planet in advance of the Cambrian radiation. The details of Gondwana assembly associated with the closure of the Mozambique Ocean are enigmatic. We compile published geological and paleomagnetic data to argue that the Tarim block was associated with the Azania and Afif-Abas-Lhasa terranes and they were the locus of long-lived Andean-type subduction during the~900-650 Ma interval. Our model suggests a subduction system reorganization between 750-720 Ma, which resulted in two distinct phases of Mozambique ocean evolution. Between 870-750 Ma, a N-S oriented subduction system marks the locus of ocean crust consumption driven by the extension of the Mozambique Ocean. Beginning~720 Ma, a newly developed~E-W oriented subduction system began to consume the Mozambique Ocean and led to the assembly of eastern Gondwana. Our new reconstruction uses true polar wander to constrain the relative paleo-longitude of Tarim, South China and West Africa. In this scenario, the closure of the Mozambique Ocean and formation of Gondwana was orthogonal to the preceding super-continent Rodinia.
... Whereas the Maud Complex, Barue Complex and Nampula Terrane are correlatable (Grantham et al., 2011, there are significant differences between the geology underlying Central Dronning Maud Land (CDML) and the Nampula Terrane which are juxtaposed in reconstructed Gondwana (Fig. 1b). The geology of DML is a subject of debate between differing views of the extent of, and relationships between, the East African Orogeny (EAO) (Stern, 1994) and the Kuunga Orogeny (Meert, 2003) (Figs. 1a and 1b). ...
... Grantham et al. (2008) similarly infer a major crustal boundary along the Lurio Belt of N. Mozambique (Fig. 1b) and suggested it is correlatable with the boundary separating the Highlands and Vijayan Complexes in Sri Lanka, located to the east in a reconstructed Gondwana (Fig. 1b). Meert (2003) recognized a younger E-W oriented belt cross-cutting the EAO, termed the Kuunga Orogeny, extending westwards through the Zambezi Belt to the Damara Belt of Namibia and eastwards through Dronning Maud Land, Antarctica into Sri Lanka (Fig. 1a). The Kuunga Orogeny is also recognized east of Enderby Land, in the Prince Charles Mountains and at Prydz Bay (Boger, 2011), the Denman Glacier area of Antarctica (Daczko et al., 2018) and in China (Li et al., 2017). ...
... Differences in ages between the KO and EAO are 530-570 Ma and 650-900 Ma respectively (Stern, 1994;Meert, 2003). Bingen et al. (2011) also recognized overprinting of EAO lithologies by the KO progressing southwards toward the Lurio Belt in N. Mozambique. ...
The ~550 Ma Kuunga Orogeny extends from the Damara in Namibia, through the Zambesi and Lurio orogenic belts in Zambia and Mozambique, southern Africa, through Dronning Maud Land and Princess Elizabeth Land, Antarctica into western Australia. Sverdrupfjella is located at the western end of Dronning Maud Land where the Kuunga Orogeny is inferred to post-date and overprint the East African Orogeny.
Three complexes are recognized in Sverdrupfjella western Dronning Maud Land , Antarctica. A western basal ~1140 Ma Jutulrora Complex, consisting mostly of arc-related tonalitic trondjhemitic orthogneiss with evolved Sr - Nd isotopic signatures with TDm ages >2 Ga. It is structurally overlain by the Fuglefjellet Complex, comprising supracrustal ~800 – 900 Ma carbonates intercalated with quartzo-feldspathic gneisses with detrital zircons of ~1000 - 1200 Ma age with ~500 Ma overgrowths. The Fuglefjellet Complex is overlain in the east by the Rootshorga Complex containing paragneisses with minor orthogneisses (~1100 – 1200 Ma), intruded by granitic orthogneiss of similar age. Strontium - Nd isotopic signatures from the Rootshorga Complex has TDm ages <1.8 Ga.
D1 and D2 planar fabrics typically dip to SE with vergence top-to-NW in all complexes. D3 deformation verges top-to-the-SE. In the Jutulrora Complex, D3 comprises ~100m scale folds with NW dipping axial planes, cut by SE dipping dilational granite sheets. In the Rootshorga Complex D3 is characterised by syntectonic granite veins with extensional and compressional displacements with top-to-the SE shear. Discordancies are consistent with low angle thrust planes at Fuglefjellet and Kvikjolen with probable repetition of carbonate layers.
Zircon ages of the granitic sheets are 490 - 500Ma. Strontium and Nd isotopic signatures of the granitic sheets intruded into all complexes are consistent with melting of Jutulrora Complex crust with Archaean and Mesoproterozoic xenocrysts in some samples. Top-to-SE shear zones displace pegmatites with an inferred age of 520 Ma and are syntectonic with layer parallel ~490 Ma granite sheets.
P-T-t studies from the Rootshorga Complex yield isothermal decompression paths at ~ 800 – 900 oC with decompression from ~1.4 GPa at ~570Ma to ~700oC and ~0.7 GPa at ~500Ma whereas P-T-t estimates from the Jutulrora Complex are ~ 600 – 700 oC and <~0.8 GPa at ~500 Ma with a path consistent with crustal loading. The Rootshorga and Fuglefjellet Complex are inferred to comprise a mega-nappe, emplaced during the Kuunga Orogeny ~500 Ma ago, over the footwall Jutulrora Complex. Aerogravity, satellite gravity and seismic tomography data reflecting unusually thick crust are consistent with this interpretation.
... During the Ediacaran-Cambrian transition, the Yangtze Block, bordered by two narrow margin-slope zones along the northern and south-southwest flanks (Chen et al., 2009), experienced significant geological changes influenced by global continental rearrangements. Specifically, these changes included the rifting of Laurentia from western Gondwana (Meert, 2003) and the simultaneous amalgamation of Australia with East Antarctica and eastern Gondwana, which coincided with the collision between East and West Gondwana (Kirschvink, 1992;Meert, 2003). These tectonic events indirectly influenced sedimentation patterns on the Yangtze Platform (Goldberg et al., 2007). ...
... During the Ediacaran-Cambrian transition, the Yangtze Block, bordered by two narrow margin-slope zones along the northern and south-southwest flanks (Chen et al., 2009), experienced significant geological changes influenced by global continental rearrangements. Specifically, these changes included the rifting of Laurentia from western Gondwana (Meert, 2003) and the simultaneous amalgamation of Australia with East Antarctica and eastern Gondwana, which coincided with the collision between East and West Gondwana (Kirschvink, 1992;Meert, 2003). These tectonic events indirectly influenced sedimentation patterns on the Yangtze Platform (Goldberg et al., 2007). ...
Marine shale gas has emerged as a prominent unconventional petroleum resource in recent years, known for its abundant reserves and energy potential. Based on the database of geochemical, mineralogy and physical lab measurements, this study investigates the paleoenvironmental conditions and shale gas potential of the Carboniferous Dawuba and Cambrian Niutitang shales in the Upper Yangtze Platform, South China. Analysis of the paleoclimate and water conditions reveals that the Dawuba shale was deposited under a warm and arid climate with reducing conditions that favored organic matter (OM) preservation, transitioning towards marine conditions with increasing salinity. The Niutitang shale experienced a cooler, arid climate with prevalent saltwater and reducing conditions, also conducive to OM preservation. Both formations have reached the post-mature stage, displaying good to excellent source rock potential. The Dawuba shales are characterized by Type II2 kerogens, while the Niutitang shales predominantly contain Type I kerogens, indicating high gas generation potentials for both. The formations are composed of mixed and argillaceous shales, exhibiting ultra-low porosity and permeability but featuring development of dissolution pores, OM pores, and micro-fractures essential for gas storage. Comparative analysis shows the Dawuba shales have superior BET-specific surface areas, total pore volumes, and average pore diameters than the Niutitang shales. However, gas contents in both formations are relatively low, underscoring the necessity for further research on shale gas preservation conditions. The Qiannan Depression in Guizhou, particularly the Shangyuan and Zongdi areas of the Dawuba Formation, are identified as promising regions for shale gas exploration due to favorable geological characteristics. This study highlights the significant shale gas potential in the Upper Yangtze Platform and calls for focused research to optimize exploration and extraction efforts.
... The Grenvillian Orogeny (1.3-0.9 Ga) is extensively recorded in both Laurentia and Gondwana (Fig. 7c-j) (Fitzsimons, 2000;Meert, 2003;Wang et al. 2016;Olieook et al. 2019). In northern East Gondwana, Sibumasu also contains a significant percentage of Greenlandian detrital zircons (Cai et al. 2017;Wu et al. 2023). ...
... Palaeomagnetic results show that during the Pan-African Orogeny, India, East Antarctica, and Australia converged to form East Gondwana (Fitzsimons, 2000(Fitzsimons, , 2003Powell et al., 2001;Pisarevsky et al., 2003). From 570 to 510 Ma, the collision of India-Antarctica and Australia-Antarctica resulted in the formation of the Kuunga Orogeny (Meert, 2003;Meert & Lieberman, 2008;Boger, 2011). The area between India and Western Australia, which is called the Pinjarra Orogen (Fitzsimons, 2003;Harley et al. 2013), records significant regional deformation and high-grade metamorphism because of convergence (Halpin et al. 2008;Pankhurst et al. 2008;Boger, 2011). ...
During the existence of Proto-Tethys Ocean (550–430 Ma), microcontinents in northern East Gondwana merged with the northern margin of India-Australia, completing the assembly of Gondwana. Ongoing controversy surrounds the disappearance of the Proto-Tethys Ocean, the dynamic mechanisms of suturing and the palaeogeographic relationships among microcontinents in northern East Gondwana, contributing to the uncertainty about the tectonic evolution of the region. This paper concerns the lower Silurian Zusailing Formation in the Hainan Island and focuses on the affinity between Hainan Island and various microcontinents in northern East Gondwana during the early Silurian. We use detrital zircon geochronology to reconstruct the closure process of the Proto-Tethys Ocean and show that the detrital zircon U–Pb age groups of the lower Silurian Zusailing Formation are 2800–2200, 2100–1350, 1250–950, 600–480 and 480–430 Ma, with a significant age peak of ca. 449 Ma. Furthermore, the analysis of detrital zircon geochemistry and europium anomalies shows that the Hainan Island crust continued to thicken during 600–434 Ma. Comparing the age spectrum of early Palaeozoic detrital zircons from Hainan Island and various microcontinents in northern East Gondwana, as well as the affinity among them during the Silurian, we conclude that the closure of the eastern Proto-Tethys Ocean evolved from unidirectional subduction (600–480 Ma) to bidirectional subduction (480–430 Ma).
... The late Neoproterozoic to Cambrian history of East Africa is characterized by two major thermal events. The periods from approximately 750 to 620 Ma [69,70,86,87] and 580 to 510 Ma [88,89] are thought to relate to the closure of the Mozambique Ocean, resulting in the amalgamation of Gondwanaland. There are contrasting opinions as to which period represents the final closure of the ocean. ...
... Hulscher and Fitzsimons [93] suggested that tectonism between 580 and 510 Ma was largely driven by extension in the early closure model based on patterns of tectonic deformation at approximately 550 Ma observed in central Madagascar, whereas convergencerelated shortening predominated in the model for final amalgamation at approximately 550 Ma; this is consistent with age determinations for the Angavo shear zone [69,86,92]. At approximately 540 Ma, deformation in the cover was dominated by sinistral transpression, which continued until approximately 530 Ma, when lateral escape could no longer be accommodated. ...
Madagascar is globally recognized as an important producer of high-quality flaky graphite. However, current research on graphite deposits in Madagascar remains insufficient. Previous studies have linked the genesis of Madagascan graphite deposits to the metamorphism of sedimentary organic matter. Here, we provide a case study of graphite deposits in Madagascar, combining new data from the Ambahita graphite deposit (AMG) in southern Madagascar with data from the Antanisoa graphite deposit (ANG) in central Madagascar and the Vohitasara graphite deposit (VOG) on the east coast of Madagascar. We note that the mineral assemblages of graphite-bearing rocks in the AMG, ANG, and VOG are not typical of metamorphic mineral assemblages but rather the results of filling and metasomatism by mantle-derived fluids that occurred after peak metamorphism. Electron microprobe analysis indicates that the graphite of the AMG, VOG, and ANG is usually associated with phlogopite or Mg-biotite; the phlogopite shares a common genesis with other widespread phlogopite deposits across Madagascar. We reveal that the distribution of graphite deposits in Madagascar is primarily controlled by ductile shear zones between blocks. Ductile shear zones that extend deep into the mantle can provide an ideal migration channel and architecture for the emplacement of mantle-derived fluids. The graphite mineralization formed no earlier than the peak metamorphism (490 Ma) and no later than the intrusion of pegmatite veins (389 ± 5 Ma). The distribution of graphite deposits, graphite orebody morphologies, mineral associations, and geochemical data suggest that the genesis of graphite deposits in Madagascar is linked to mantle-derived fluid filling rather than the metamorphism of sediments, as previously suggested. These findings have important implications for similar deposits in Madagascar and potentially globally.
... The youngest, and likely therefore least overprinted and easiest to interpret, structural episode was a period of collisional orogenesis that saw amphibolite and granulite grade metamorphism at~560-500 Ma (e.g. Axelsson et al., 2020;Boger, 2011;Kröner and Williams, 1993;Meert, 2003;Veevers, 2009). ...
... They proposed that the Marion plume's ascent and spread beneath the southern part of this boundary applied Figure 11 -Fit reconstruction in present-day India reference frame. 1: structural trends in selected terranes, in Antarctica from magnetic anomalies (Golynsky et al., 2018a), in India after Wandrey (1998) and Axelsson et al. (2020), and in Sri Lanka after Kröner et al. (2003) (Axelsson et al., 2020;Meert, 2003;Veevers, 2009). 5: Late Paleozoic-Mesozoic Godavari (G) and Mahanadi (M) basins. ...
Models of past plate motions in the Indian Ocean help map the supercontinent Gondwana and investigate how mantle plumes influence plate tectonics. Reducing confidence in this, however, the range of available models all produce large pre-94 Ma movements, in various kinematic senses, between India and Madagascar. There is no observational evidence for any of these motions, suggesting along with their diversity that they are artefacts stemming from contrasting resolutions of techniques used for reconstructing India and Madagascar to Antarctica. A higher resolution approach to India-Antarctica reconstruction concentrates on geophysical records of relative plate motion azimuths. Applying its results regionally eliminates Indo-Malagasy motions before 94 Ma, and prompts new hypotheses of two small tectonic plates. The early Cretaceous Mandara plate, in the Enderby Basin off East Antarctica, may have initiated and rotated at a mid-ocean ridge that was supplied by excess melt from the Kerguelen plume. The late Cretaceous Vasuki plate may have conveyed Sri Lanka southwards across the western Bay of Bengal. The 85°E and Comorin ridges may have formed at active transform fault zones along Vasuki's margins that were supplied with excess melt from the Crozet and Marion plumes. The model confidently implies the presence of 500,000 km 2 of continental crust beneath the Kerguelen Plateau, places Sri Lanka 1000 km further east within Gondwana than previous reconstructions, and casts doubt on the existence of plate kinematic signals that have previously been attributed to the arrival and spread of the Marion plume beneath India and Madagascar at~105 Ma.
... The Pan-African Movement (PAM) was a Precambrian-Cambrian tectonic movement across the African continent and Gondwana. This crustal movement was primarily characterized by tectonic-thermal events [59]. It resulted from the collision of a series of micro-plates, forming the stable Precambrian crystalline basement of the large "Pan-Cratonic Basin" in the Middle East-North Africa, which is clearly exposed in the Arabian Shield in the Middle East and the Hoggar Shield in southern Algeria in North Africa ( Figure 3). ...
... The Pan-African Movement (PAM) was a Precambrian-Cambrian tectonic movement across the African continent and Gondwana. This crustal movement was primarily characterized by tectonic-thermal events [59]. It resulted from the collision of a series of microplates, forming the stable Precambrian crystalline basement of the large "Pan-Cratonic Basin" in the Middle East-North Africa, which is clearly exposed in the Arabian Shield in the Middle East and the Hoggar Shield in southern Algeria in North Africa ( Figure 3). ...
In this study, we elucidate the genesis and distribution patterns of Silurian hot shale hydrocarbon source rocks by utilizing a comparative analysis of the evolutionary characteristics of plate tectonic activity in the Paleo–Tethys Ocean and the sedimentary filling characteristics of key basins in North Africa, the Middle East, and South China. We propose an explanation for the sedimentary genesis of world-class Silurian hydrocarbon source rocks in the Paleozoic craton basin of the ancient Tethys tectonic domain. This is achieved by scrutinizing the plate tectonic activity and evolution of the ancient Tethys Ocean and combining these findings with the paleotectonic sedimentation background of North Africa, the Middle East, and South China. Additionally, we compare Silurian hydrocarbon source rocks from these regions. The deep-water stagnant environment of the land shelf favors the preservation of organic matter, thereby forming high-quality hydrocarbon source rocks. Conversely, the shallow-water body of the land shelf is more turbulent, thus resulting in the poorer preservation of organic matter and, consequently, lower-quality hydrocarbon source rocks.
... Subsequent to Mesoproterozoic events, the "Pan-African" orogeny is a broad term to describe the protracted Neoproterozoic to Cambrian orogeny in Africa. High-grade metamorphism attributed to this orogeny in eastern and southern Africa ranges from ca. 800 to 470 Ma (compilation in Meert, 2003). Three main frequency maxima of tectonic activity are apparent in the data, at ca. 760 to 730 Ma, 660 to 610 Ma and 570 to 530 Ma, respectively. ...
... Three main frequency maxima of tectonic activity are apparent in the data, at ca. 760 to 730 Ma, 660 to 610 Ma and 570 to 530 Ma, respectively. The third of these events is referred to as the "Kuunga orogeny" by Meert (2003). ...
The geology of northeastern Mozambique has been remapped at 1:250 000 scale. Proterozoic rocks, which make up the bulk of
the area, form a number of gneiss complexes defined on the basis of their lithologies, metamorphic grade, structures, tectonic
relationships and ages. The gneiss complexes, which contain both ortho- and paragneisses, range from Palaeo- to Neoproterozoic
in age, and were juxtaposed along tectonic contacts during the late Neoproterozoic to Cambrian Pan-African Orogeny. In this paper
we describe the geological evolution of the terranes north of the Lurio Belt, a major tectonic boundary which separates the
complexes described in this paper from the Nampula Complex to the south. The Marrupa, Nairoto and Meluco Complexes are
dominated by orthogneisses of felsic to intermediate compositions. Granulitic rocks, including charnockites, are present in the
Unango, M’Sawize, Xixano and Ocua Complexes (the last forms the centre of the Lurio Belt). The Neoproterozoic Geci and
Txitonga Groups are dominated by metasupracrustal rocks at low metamorphic grades and have been tectonically juxtaposed with
the Unango Complex. Geochemical data integrate and support a model of terrain assembly in northeast Mozambique, which is
largely published and mainly derived from our new geochronological, lithostratigraphic and structural work. This model shows
the contrast between the mainly felsic lower tectonostratigraphic levels (Unango, Marrupa, Nairoto and Meluco Complexes) and
the significantly more juvenile overlying complexes (Xixano, Muaquia, M’Sawize, Lalamo and Montepuez Complexes), which were
all assembled during the Cambrian Pan-African orogeny. The juxtaposed terranes were stitched by several suites of Cambrian
late- to post-tectonic granitoids.
... The ANS was initially established between ca. 900-650 Ma as part of the northern activities of the East African Orogeny (EAO) [4][5][6][7][8]. The ANS in the North Eastern Desert (NED) and Sinai are equivalent, dominated by posttectonic (ca. ...
... The whole Red Sea rift system Is flanked by the basement rocks of the ANS, which were initially formed by mass accumulation of continental fragments, island arcs, and oceanic plateaus during the EAO in the time span from ca. 900 to and 650 Ma [6,8]. These basement rocks in Egypt are constructed mainly of (1) the island arc suite representing the EAO's oldest activity that prolonged between ca. ...
The Suez Rift developed as a northern extension of the Red Sea rift during the Oligocene-Miocene, whose flanks were constructed from the Neoproterozoic basement rocks of the Arabian–Nubian Shield. These basement rocks are comprised of the whole tectonic history since their formation. The Suez Rift initiation model and proposed thermal overprint role in the rifting process and flank development remain uncertain. Additionally, the amplitude of different regional tectonic events’ effects on the region is still debatable. Integration of fission-track thermochronology data with modeling of the time-temperature history has demonstrated efficiency in addressing such issues. In the context of this study, eleven representative samples were collected from the different rock units in the Wadi El-Dahal area at the northern tip of the western flank of the Suez Rift. These samples revealed Carboniferous zircon fission-track cooling ages of 353 ± 9 Ma and 344 ± 11 Ma. Meanwhile, the apatite fission-track analysis provided two spatially separated age groups: Permian-Triassic and Late Cretaceous, with average ages of 249 ± 11 Ma and ca. 86 ± 10 Ma, respectively. The time-temperature modeling revealed four possible cooling pulses representing exhumation events, which were initiated as a response to four tectonic activities: the accretion-subsequent event of erosion during the Neoproterozoic, the Hercynian (Variscan) tectonic event during the Devonian-Carboniferous, the Mid-Atlantic opening during the Cretaceous, and the Suez Rift opening during the Oligocene-Miocene. The western flank of the Suez Rift suggests a passive mechanical type with no extra thermal overprint, as indicated by the dominance of older thermochronological ages, modest rift flank elevations, and a reduction in the heat flow.
... These rocks underwent metamorphism with clockwise pressure (P)-temperature (T ) trajectories (e.g., Hiroi et al., 1983a;Shiraishi et al., 1994;Motoyoshi and Ishikawa, 1997;Yoshimura et al., 2008;Kawasaki et al., 2011), with the exception of the early Neoproterozoic metamorphic rocks of Cape Hinode (Dunkley et al., 2014). The complex has long been recognized as one of key regions to any reconstructions of the Gondwana supercontinent, which can be viewed as a single long-lived orogenesis, the 'East Africa-Antarctic Orogen (EAAO)' (Jacobs and Thomas, 2004) or a series of orogens, 'East African Orogeny (EAO)' and 'Kuunga Orogeny (KO)' (Meert, 2003) (Fig. 1). The large-scale continent-continent collision between the west and east Gondwana produced the EAAO during~650-500 Ma (Jacobs and Thomas, 2004) (Fig. 1a). ...
... The westward collision of the~1130-1040 Ma metamorphic terrane of the Maud Belt to the Proto-Kalahari Craton in the south part of the EAAO was followed by the accretion of the Tonian Oceanic Arc Super Terrane which is a series of juvenile oceanic arcs formed around 1000-900 Ma (Fig. 1a). An alternative proposal by Meert (2003) (Fig. 1b) is that the Gondwana assembly was initiated by the N-S trending EAO during~750-620 Ma, and was completed by the E-W trending KO at some 570-530 Ma. Thus, it is obvious that an understanding of the geological events that have affected the LHC is central to constraining any of the proposed models of the tectono-thermal history of the central part of the Gondwana supercontinent. ...
This paper reports laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) zircon U–Pb ages of a suite of high-grade metamorphic rocks collected from Sinnan Rocks, Akebono Rock, Niban Rock, Gobanme Rock, Tenmondai Rock, Akarui Point, Cape Omega, and Oku-iwa Rock along the Prince Olav Coast, in the Lützow-Holm Complex (LHC), East Antarctica. The dating results indicate that a newly detected ~ 990 Ma metamorphism of garnet–sillimanite–biotite gneiss from Niban Rock. A thermal event at 931.7 ± 9.8 Ma is recorded in zircon from staurolite-bearing garnet–gedrite–biotite–chlorite gneiss in Akebono Rock. The metamorphic zircon grains in other analyzed samples provide Ediacaran to Cambrian ages. Their multi-growth textures and age populations are possibly interpreted to exhibit three metamorphic stages during >600–580 Ma, 580–550 Ma, and 550–500 Ma. Combined with previous reports, the metamorphic rocks in Cape Hinode, Niban-nishi Rock of Niban Rock, and Akebono Rock might have experienced earlier high-temperature metamorphism at ~ 990–930 Ma without younger overprinting. Extensive high-grade metamorphism during ~ 650–500 Ma is recorded from not only the granulite-facies zone in the west of the LHC but also the amphibolite-facies zone in its east. The main metamorphic episode in the LHC is likely to be subdivided into a preceding thermal event (either independent single metamorphic event or prograde stage) at pre-580 Ma, near-peak condition stage during 580–560 Ma, and subsequent retrograde stage after 550 Ma. In regional context this indicates that the assembly at the central Gondwana started with the collision of early and late Neoproterozoic terranes prior to 580 Ma, as a part of the East Africa-Antarctic Orogeny. Subsequent collisions took place among late Neoproterozoic igneous terrane, above terranes collided at pre-580 Ma, and Neoarchean terrane, which were probably driven by the Kuunga Orogeny.
... Africa and Antarctica split apart between the Kalahari Craton and Dronning Maud Land along 580-550 Ma-old Pan-African orogens (Bauer et al. 2003;Veevers 2003;Buiter and Torsvik 2014). When Gondwana split apart, the breakup progressed to eventually separate India from Africa along the East African Orogen, along which eastern Africa and India-Madagascar had previously collided to form Gondwana after the breakup of Rodinia (Meert 2003;Gray et al. 2008;Li et al. 2008). ...
... Ridge jumps and the formation of microcontinents between India and Australia, which also began about 160 Ma, were associated with the rifting process. The oldest known magnetic anomalies show that India broke away from Antarctica and Australia at 132 Ma, with most of the breakup occurring along the Gondwana-forming 610-510 Ma-old Kuugan Orogen (Meert 2003;Gray et al. 2008). ...
What drives the breakup of a supercontinent remains contentious. Previously proposed mechanisms include mantle plumes, subduction retreat, and basal traction from mantle convection. Here we review the geological record of plumes, orogens, and subduction zones during the Pangea breakup and investigate the potential roles played by these factors through 4D spherical geodynamic modelling. We found that mantle plumes provided the dominant force that drove Pangea's breakup, particularly in triggering the initial breakup. Young orogens as continental lithospheric weak zones generally guided the development of continental rifts, consistent with the geological record that rifting within Pangea commonly developed along pre-existing orogens. However, the marginal drag force produced by subduction retreat, and basal traction associated with subduction-related mantle flow, likely also played a role in Pangea's breakup. In addition, the weakening effect of plume-induced melts can sometimes help to break the continental lithosphere away from orogens, as exemplified by the breakup between Antarctica and Australia. Furthermore, geodynamic modeling suggests that subduction is responsible for generating mantle plumes. A particular such example is the formation of the Kerguelen plume, triggered by subduction along the northern margin of Australia, which facilitated the breakup between East Antarctica and Australia.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6670136
... 530-470 Ma Andean-type orogen (i.e., Bhimphedian orogen) along the Indian-Australian Gondwanan margin (Cawood et al., , 2021. By contrast, they are comparable with those of the 560-520 Ma Kuunga-Pinjarra interior orogen (Kuunga-Pinjarra interior orogen) of East Gondwana ( Fig. 9; Meert et al., 1995;Meert, 2003;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007;Gray et al., 2008). Therefore, the Bureya-Jiamusi-Khanka superterrane may be a missing part of the Kuunga-Pinjarra interior orogen, which extends thousands of kilometers from the Maud Queen's Land, Lytso-Holm Bay, and Pritz Bay-Grove Mountain of East Antarctica via the Eastern Ghats Belt of Eastern India to the Darling-Pinjarra of Western Australia (Meert et al., 1995;Meert, 2003). ...
... By contrast, they are comparable with those of the 560-520 Ma Kuunga-Pinjarra interior orogen (Kuunga-Pinjarra interior orogen) of East Gondwana ( Fig. 9; Meert et al., 1995;Meert, 2003;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007;Gray et al., 2008). Therefore, the Bureya-Jiamusi-Khanka superterrane may be a missing part of the Kuunga-Pinjarra interior orogen, which extends thousands of kilometers from the Maud Queen's Land, Lytso-Holm Bay, and Pritz Bay-Grove Mountain of East Antarctica via the Eastern Ghats Belt of Eastern India to the Darling-Pinjarra of Western Australia (Meert et al., 1995;Meert, 2003). This raises a question: Where should the Bureya-Jiamusi-Khanka superterrane be located within the Kuunga-Pinjarra interior orogen? ...
There is general agreement that a series of East Asian blocks has always lain outboard of both India and Australia along the North Indo−Australie peripheral orogen. However, whether the East Asian blocks were involved in the interior orogens of East Gondwana remains equivocal. The geochronology and geochemistry of Neoproterozoic−Late Triassic rocks in the Russian Far East, together with existing paleontological and detrital zircon data, offer an opportunity to determine the tectonic origin and drift history of the Bureya−Jiamusi−Khanka superterrane. Biotite and amphibole 40Ar/39Ar dating results define a distinctive episode of Late Pan-African (ca. 550 Ma) metamorphism and a local Late Triassic (ca. 219−200 Ma) episode of deformation for the Bureya−Jiamusi−Khanka superterrane. Zircon U−Pb ages and whole-rock geochemical data indicate that the Early Ordovician (483 ± 3 Ma) highly fractionated I-type monzogranites were emplaced in a post-collisional setting linked to the collapse of a Late Pan-African orogen, while the Late Triassic (ca. 234−223 Ma) A-type quartz syenites and I-type granite aplite dikes were formed in a slab-pull−induced passive continental margin of the subducting Mudanjiang oceanic plate. These crucial archives, complemented by data from the literature, reveal that the Bureya−Jiamusi−Khanka superterrane made up the northernmost Kuunga-Pinjarra interior orogen during the final assembly of East Gondwana. As a result of Devonian rifting after Early Ordovician orogen collapse, the Bureya−Jiamusi−Khanka superterrane escaped from the Kuunga-Pinjarra interior orogen and subsequently migrated to Northeast Asia by the Late Triassic to Jurassic due to the subduction and closure of the Paleo-Tethys and Paleo-Pacific oceans.
... The ANS is dominated by low-grade volcano-sedimentary rocks associated with plutons and ophiolitic remnants [4,[15][16][17][18][19], and represents the juvenile terrane. However, the MB in the south part of the EAO is a tract of largely older continental crust that was extensively deformed and metamorphosed in the Neoproterozoic/Cambrian ( [10,[20][21][22]; Figure 1). Minerals 2024, 14, x FOR PEER REVIEW 3 of 20 Figure 1. ...
The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO2) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K2O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (87Sr/86Sr)i values of 0.70088 to 0.70275, positive εNd(t) values of 3.26 to 7.28, together with the positive εHf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al2O3 in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny.
... The Sinsk event followed a long phase of Neoproterozoic to early Paleozoic global tectonic reorganization, including breakup of the supercontinent Rodinia and reassembly of most cratonic masses into Gondwana (5). Collisional suturing during the East African and Kuunga orogenies culminated in amalgamation of East Gondwana (modern Africa, Antarctica, Australia, and India) during the Cambrian (6). Gondwana supercontinent assembly included suturing along the East African-Antarctic Orogen, broadly fusing East (Indo-Antarctica) and West (Africa) Gondwana between ~600 and 540 Ma (7)(8)(9)(10). ...
The Cambrian explosion, one of the most consequential biological revolutions in Earth history, occurred in two phases separated by the Sinsk event, the first major extinction of the Phanerozoic. Trilobite fossil data show that Series 2 strata in the Ross Orogen, Antarctica, and Delamerian Orogen, Australia, record nearly identical and synchronous tectono-sedimentary shifts marking the Sinsk event. These resulted from an abrupt pulse of contractional supracrustal deformation on both continents during the Pararaia janeae trilobite Zone. The Sinsk event extinction was triggered by initial Ross/Delamerian supracrustal contraction along the edge of Gondwana, which caused a cascading series of geodynamic, paleoenvironmental, and biotic changes, including (i) loss of shallow marine carbonate habitats along the Gondwanan margin; (ii) tectonic transformation to extensional tectonics within the Gondwanan interior; (iii) extrusion of the Kalkarindji large igneous province; (iv) release of large volumes of volcanic gasses; and (v) rapid climatic change, including incursions of marine anoxic waters and collapse of shallow marine ecosystems.
... The Arabian-Nubian Shield was formed (ca. 900-550 Ma) during the East African Orogeny through accretion of island arcs and microcontinental fragments onto Archean continental crust or via the accretion of juvenile crust (e.g., Azer et al. 2014;Abbo et al. 2020;Stern 1994;Meert 2003;Ali et al. 2013;Mahdy et al. 2015;Adam et al. 2020). The granitoid rocks at Sinai Peninsula belong to the late of Pan-African activity that marked by some syn-and post-tectonic granitoids (e.g., Sturchio et al. 1985;Willis et al. 1988). ...
This paper discusses the geochemical constraints on genesis of dispersed mineralized quartz-fluorite veins (QFV) at south west Sinai Peninsula, Egypt. These veins range from colorless to pale to deep violet in color and extend continuously and/or discontinuously in NE-SW, E-W, N-S, and NW-SE trends. They exhibit varying thicknesses ranging from a few centimeters to approximately 0.3 m. The scanning electron microscope (SEM) analysis has revealed the existence of secondary uranium minerals, notably kasolite Pb(UO2)SiO4.(H2O), in association with other minerals such as galena (PbS), atacamite (Cu2Cl(OH)3), and fluorite (CaF2) within the quartz-fluorite veins (QFV). Furthermore, the SEM analysis indicates a significant presence of fluorine incorporated into the biotite lattice of the host granitic rocks. Geochemically, there is a reasonable difference between the host granitic rocks and QFV, especially, silica and alumina contents. Also, some trace elements experienced enrichment in QFV such as Cu, U, Pb and Ag. The chondrite normalized pattern of QFV rare earth elements (REE) shows conspicuous negative Tb anomalies while the host rocks showed negative Eu anomalies. It is noticeable that there is a closed relation between uranium and fluorine in QFV. The Th/U ratios are < 1 in QFV samples indicating that the QFV had not been derived from magmatic origin. Furthermore, the REE and the mineral assemblages of QFV imply to hydrothermal origin (meteoric water) at shallow depth and low temperature < 200 °C under oxidation condition (epithermal genesis).
... Gem-zircon-bearing pegmatites in southern Malawi formed during this episode (Chakraborty et al. 2023). The subsequent assembly of Gondwana led to closure of the oceanic basins during the ~ 690-600 Ma East-African Orogeny (collision of East and West Gondwana) and the ~ 580-520 Ma Kuunga Orogeny (collision of the Kalahari Craton, Dronning Maud Land/Antarctica; e.g., Grantham et al. 2003Grantham et al. , 2013Meert 2003;Fritz et al. 2013;Oriolo et al. 2017; Fig. 1). All pegmatites discussed here formed between 555 and 485 Ma and are related to the Kuunga Orogeny and its post-orogenic aftermath (Chakraborty et al. 2023). ...
Late-Pan-African granitic pegmatites in Malawi host gem mineralization (tourmaline, beryl/aquamarine/heliodor). We use major and trace element chemistry of mica and tourmaline as proxies to describe the geochemical characteristics and to analyze the evolution of the pegmatite-forming melts. Trace element contents and ratios of pegmatitic micas and tourmalines show characteristic fractionation trends. Mica from highly fractionated pegmatite typically shows high Rb, Cs, Zn, Nb, Ta, F, and Li concentrations but low Ni, Co, V, Ti and Sc concentrations. In their less fractionated counterparts, these compositional patterns are largely reversed. Exceptions in these element patterns are related to the presence or absence of other phases that may fractionate specific elements more strongly than mica. Tourmaline shows similar fractionation trends in major and trace elements. The observed patterns indicate fractional crystallization as the dominant process of melt evolution. A near exponential decrease of alkali element ratios, such as K/Rb and K/Cs, and an increase in Rb, Cs and Li in white mica from the less to the more strongly differentiated zones suggest Rayleigh fractional crystallization. The modelling of these element ratios shows that in different pegmatite bodies the least differentiated zone formed at a fractionation coefficient of F = 0.35–0.5. Zones of intermediate fractionation show F = 0.85–0.9. Gem mineralization is associated with the most highly fractionated pegmatites or pegmatite zones (F = ~ 0.99). These highly fractionated pegmatites show strong enrichment of Li, Rb and Cs in mica and tourmaline forming from melts rich in incompatible elements. The crystallization of gem phases depended on this highly enriched environment.
... Re-Os isotopic plots reflect the role of ancient depleted SCLM and the large variations in ɣ Os values attest to involvement of both SCLM and depleted MORB component thereby contributing to pronounced Os isotopic heterogeneities in the upper mantle that in turn manifest inputs of discrete depleted and enriched mantle components during opening and closure of ocean basins synchronized with assembly and dispersal of continental blocks (Tsuru et al., 2000). The 720 to 549 Ma melt extraction ages for the studied samples correspond to multiple melt extraction and mantle depletion events preceding the opening of Neo-Tethyan seaway and SCLM delamination concurrent with subduction driven ocean basin closure and amalgamation of Gondwana Supercontinent (Fig. 9a) (Meert and Van der Voo, 1997;Rogers and Santosh, 2003;Meert, 2003). The model ages 1142 Ma and 466-250 Ma possibly indicate some melt extraction in the sub-continental lithospheric mantle of Rodinia and Pangea supercontinent respectively. ...
... Therefore, the original magma of the K-bentonites from the two sections may come from the crust. Some workers (Meert, 2003;Kröner and Stern, 2004;Mukhopadhyay and Basak, 2009) believe that there is still crustal movement in the form of tectonic-thermal events caused by the Pan-African orogeny during 600-550 Ma, resulting in the formation of the Gondwana supercontinent. The intense tectonic movement will trigger a series of volcanic activities. ...
Several K-bentonite beds have been discovered in the upper part of the Ediacaran system in South China. Existing researches mainly focus on the zircon U-Pb geochronology of the K-bentonites. However, the nature of the primary magmas of the K-bentonites, the tectonic setting of their source volcanoes, the significance of their geochemical correlation, and their potential implications to evolution of late Ediacaran life have not been unraveled. Here, whole-rock and zircon geochemical studies have been carried out on the K-bentonites in the top of the Miaohe Member from the Jiuqunao section, and in the basal Liuchapo Formation and the lower Dengying Formation from the Fanglong section. The major and trace element contents of the K-bentonites and the trace element contents of volcanic zircons in the K-bentonites suggest that the nature of the primary magmas of the K-bentonites
from the Fanglong and Jiuqunao sections is trachyandesitic. The oxygen isotope compositions of the volcanic zircons in the K-bentonites suggest that the source magmas of the K-bentonites from the two sections are mainly from the crust. The whole-rock Y-Nb, Ta/Yb-Th/Yb, Yb-Th/Ta, and Ta/Hf-Th/Hf diagrams, and the volcanic zircon Hf-U/Yb, Y-U/Yb, Th/U-Nb/Hf, and Th/Nb-Hf/Th diagrams of the K-bentonites show that the tectonic setting of source volcanoes of the K-bentonites was a convergent environment, which may be the result of the assembly of Gondwana during late Ediacaran. The geochemical results suggest that the K-bentonites in the basal Liuchapo Formation at the Fanglong section are correlative with the K-bentonite in the top of the Miaohe Member at the Jiuqunao section. Therefore, the geochemical correlation of the K-bentonites indicate that the age
of 550.5 ± 1.0 Ma for the K-bentonite in the top of the Miaohe Member may be too young to be used as the end time of the Doushantuo negative carbon isotope excursion (DOUNCE), and that the end time of this event should be older than the age 557 ± 3 Ma of the K-bentonite in the lower part of the Dengying Formation at the Fanglong section. Thus, the termination of the DOUNCE and the Shuram carbon isotope excursion (terminated at 567.3 ± 3.0 Ma) may be isochronous. As volcanic ashfall events are known to supply nutrients to the oceans, we hypothesise that the widespread volcanism of the late Ediacaran may have enhanced oceanic productivity and play a role in the evolution of life at this time.
... Symbols are the same as those in Fig. 3 later than the final assembly of Gondwana (ca. 570-520 Ma), hence eliminating the likelihood of Gondwana's final assembly (Meert 2003;). ...
Geochemistry, zircon U–Pb geochronology, and Hf isotope data for the Early Paleozoic granites in the Baoshan Block reveal the Early Paleozoic tectonic evolution of the Proto-Tethys. The samples are high-K, calc-alkaline, strongly peraluminous rocks with A/CNK values of 1.37–1.46, are enriched in SiO2, K2O, and Rb, and are depleted in Nb, P, Ti, Eu, and heavy rare earth elements, which indicates the crystallization fractionation of the granitic magma. Zircon U–Pb dating indicates that they formed in ca. 480 Ma. The Nansa granites have εHf(t) values ranging from − 16.04 to 4.36 with corresponding TCDM ages of 2.10–0.81 Ga, which suggests the magmas derived from the partial melting of ancient metasedimentary with minor involvement of mantle-derived components. A synthesis of data for the Early Paleozoic igneous rocks in the Baoshan block and adjacent (Tengchong, Qiangtang, Sibumasu, Himalaya, etc.) blocks indicates that these blocks were all aligned along the proto-Tethyan margin of East Gondwana in the Early Paleozoic. The Early Paleozoic S-type granites from Nansa were generated in a high-temperature and low-pressure (HTLP) extensional tectonic setting, which resulted from Andean-type orogeny instead of the final assembly of Gondwana or crustal extension in a non-arc environment. In certain places, an expanding environment may exist in opposition to the tectonic backdrop of the lithosphere's thickening and shortening, leading the crust to melt and decompress, mantle-derived materials to mix, and a small quantity of peraluminous granite to emerge.
... The final arc event recorded in this section of the Iberian Cadomian orogen overlaps the Ediacaran -Cambrian boundary. The cessation of arc magmatism may represent a shift along the Gondwana margin, and collapse of the arc sections (Stern 1994, Meert 2003Fritz et al. 2013). In the OMC, layers of andesitic-dacitic metabreccias, massive metaandesites, metarhyolites and metadacites, metacinerites, and metasedimentary rocks ( Figure 4(b)) unconformably overlie the Serie Negra Group and the metaigneous complexes. ...
The evolution of the Gondwana along the flank of the West African Craton was complex and is far from
understood. Subduction-related activity along this margin spanned between c. 750 and 500 Ma.
Sections close to African cratons record the earliest stages, while Autochthonous and Allochthonous
domains of the Variscan Belt preserve the latest stages of the arc system, essentially between c. 540 and
500 Ma. The geochemistry of the Ediacaran-early Cambrian siliciclastic series deposited along this
Cadomian active margin preserves the evolutionary history of their sources, which are related to activity
in the arc and nearby continental areas. In this sense, the SW Iberian Massif (Ossa-Morena Complex)
preserves a section of this Ediacaran-early Cambrian peri-Gondwanan arc. Its evolution can be tracked
through the characterization of the subduction-related magmatism (including the Mérida Massif) and
coeval metasedimentary record (Serie Negra Group and Malcocinado Formation) during a time interval
spanning almost 100 m.y., from pre-602 Ma to at least c. 534 Ma. This study reveals that arc magmatism
is closely linked with synorogenic deposition in a complex way so far unexplored. Arc recycling is
revealed by the isotopic equivalence of synorogenic strata to the first magmatic event (pre-602 Ma),
and by geochronological data of the arc-building pulses. The earliest magmatic pulses (c. 602–550 Ma)
are characterized by significant crustal input, likely favoured by subduction erosion. Subsequently,
magmatism evolved towards larger mantle involvement (c. 540–534 Ma), likely associated with progressive
variation in the slab angle. These slab-mantle-upper plate interactions generated changes in
the arc dynamics leading to an extensional setting with alkaline magmatism during the Cambrian. This
review proposes a model of petrogenetic and geodynamic arc evolution between the Ediacaran and
the Early Cambrian. The gathered data could improve the accuracy of future palaeogeographic
reconstructions for the northern margin of Gondwana.
... Therefore, it is necessary to establish a correlation between different continental fragments to constrain the spatiotemporal extent, which forms a necessary component for the geodynamic interpretation on a regional scale. UHT granulites from the MB, including those in this study and elsewhere, can be correlated with similar occurrences in the dispersed relics of the Gondwana supercontinent, encompassing present-day Antarctica, Australia, India, Madagascar, Africa, and South America (Meert, 2003). Although these disparate blocks have different protolith ages, the mid-lower crust of much of eastern Gondwana records evidence of high to UHT metamorphism at c. 550 Ma coinciding with the final assembly of the Gondwana supercontinent. ...
The Granulite Terrane of Southern India is a collage of Mesoarchean–Neoproterozoic crustal blocks that underwent high‐grade metamorphism associated with the final assembly of the Gondwana supercontinent during late Neoproterozoic–Cambrian. Here, we investigate the charnockites and associated sapphirine‐bearing semipelitic granulites from the eastern part of the Madurai Block (MB). We present new petrographic, mineral chemistry, and geochronological data to constrain the P – T – t evolution of the block and unravel the timescale and source of heat for the ultrahigh‐temperature metamorphism. Both the rock types contain coarse‐grained porphyroblastic garnet and orthopyroxene, yielding peak P – T conditions of 950 ± 30°C at 10.5 ± 0.8 kbar and 970 ± 40°C at 10 ± 0.5 kbar for semipelite and charnockite, respectively, using conventional thermobarometry. Peak ultrahigh temperatures are further supported by high Al content in the orthopyroxene (8.78 wt% Al 2 O 3 ) coexisting with garnet ( X Mg : up to 0.57) and feldspar thermometry of the mesoperthites and antiperthites in the semipelite, yielding 950–980°C at 10 kbar. Subsequent decompression has led to the formation of coronal orthopyroxene3 + plagioclase3 in the charnockite and symplectic orthopyroxene3 + cordierite ± sapphirine ± plagioclase3 in the semipelite, yielding P – T range of 950–850°C and 9.5–6.8 kbar for semipelites and 950–820°C and 8–6.5 kbar for charnockite. Based on the obtained P – T estimates, preserved reaction textures, and phase equilibria modelling in the MnNCKFMASHTO system, a clockwise P – T evolution with isothermal decompression followed by cooling is inferred for both the rock types.
Texturally constrained in situ monazite dating and rare earth element (REE) patterns show that the core of matrix monazite having low‐Th, Y, and extreme heavy rare earth element (HREE) depletion, yielding weighted mean ages of 582 ± 12 and 590 ± 22 Ma for semipelite and charnockite, respectively, dates the prograde evolution. The mantle of the matrix monazite in semipelite and comparable rim in charnockite, having relative Th‐enrichment compared to the core, yielding weighted mean ages of 552 ± 9 and 557 ± 13 Ma, respectively, dates extensive dissolution–reprecipitation from the melt at the peak stage. The relatively Th‐ and Y‐rich and moderately HREE‐depleted rim of matrix monazite in the semipelite, yielding weighted age of 516 ± 6 Ma, date initial garnet breakdown during post‐peak melt crystallization. By contrast, compositionally homogenous HREE + Y‐enriched monazite in the symplectite and retrograde monazites yielding weighted mean ages of 487 ± 47 Ma for semipelites and 508 ± 19 Ma for charnockites dates extensive garnet breakdown during final stages of melt crystallization and subsequent cooling. Our findings point to collision initiation at ~590 Ma, with the peak conditions attained at ~550 Ma followed by extensional collapse at ~510–490 Ma, resulting in rapid exhumation of lower crustal rocks to mid‐crustal levels under sustained ultrahigh‐temperature (UHT) conditions, followed by cooling to reach a stable geotherm. Our results suggest a long‐lived hot orogeny in the MB, where the UHT conditions were sustained for at least 40 MYr. The UHT conditions were most likely attained in the core of a long‐lived hot orogen by the combined effect of conductive heating through radioactive decay and mantle heat supply, with the former being the primary driver.
... The petrogenesis of igneous rocks and their space-time distribution in a continent-continent collision zone would provide clarification of the magmatic processes with the transition of the source region for the collisional event. Dronning Maud Land, East Antarctica was situated within a collision zone between the West and East Gondwana continents (Shiraishi et al., 1994;Jacobs et al., 2003;Meert, 2003;Asami et al., 2005;Shiraishi et al., 2008;Osanai et al., 2013). The collisional event is regarded to have a geological time scale from the late Neoproterozoic to the early Paleozoic, known as the Pan-African orogeny. ...
The Vengen Granite, one of early Paleozoic granitic rocks crops out of the southern end of the Vengen ridge, the Kanino-tsume Peak at the Main Shear Zone (MSZ) of the Sør Rondane Mountains, East Antarctica. This granite is composed of medium- to fine-grained mylonitic biotite granite and cuts the MSZ and Kanino-tsume Shear Zone. The fine-grained two-mica granitic dykes locally intrude the Vengen Granite. The two-mica granitic dykes have foliations parallel to mylonitic foliations of the Vengen Granite. The Vengen Granite is composed of plagioclase, quartz, K-feldspar, biotite, and muscovite with trace amounts of titanite, allanite, apatite, zircon and opaques as accessory minerals. The granite is geochemically characterized by a high-K content, which resembles adakitic affinity. These chemical data combined with rare earth elements and Sr-Nd isotope geochemistry suggest that the source magma of the Vengen Granite was derived from partial melting of the meta-tonalite with minor amounts of the pelitic gneisses in the SW-terrane subducted under the NE-terrane during collision of the West and East Gondwana continents.
... In addition, $750 Ma bimodal volcanic rocks are exposed in the north parts of the NASB (Fig. 1c) and were interpreted to have formed in an extensional setting . The timing of these extensional events coincides with the breakup of Rodinia (Meert, 2003;Li et al., 2008;Merdith et al., 2017). ...
The Yangtze Craton hosts significant Zn-Pb deposits in Neoproterozoic to Carboniferous carbonates (> 60 Mt Pb + Zn metals), accounting for 30% of China's Zn-Pb resources. However, determining the timing of zinc and lead mineralization in these reservoirs is challenging. This study employs LA-ICP-MS U-Pb geochronology on calcites to date Zn-Pb deposits hosted in Lower Cambrian limestone in the Huayuan orefield. Three generations of calcite formation were dated: the first recorded the pre-ore deposition of Lower Cambrian limestone at 517 ± 10 Ma, the second marked a hydrothermal event linked to stratiform sphalerite ore formation at 501.4 ± 8.4 Ma, and the third was associated with discordant breccia-hosted Zn-Pb mineralization at 397.5 ± 9.6 Ma. Our results indicate that Paleozoic carbonate-hosted Pb-Zn mineralization in the Yangtze Craton is linked to (1) the final assembly of Gondwana in the late Cambrian-early Ordovician (520 − 480 Ma); and (2) the intracontinental orogeny response to Jiangnan Uplift (420 − 400 Ma). This study highlights the spatial-temporal relationship between low temperature carbonate-hosted mineralization and orogenic events that are consistent with classic Mississippi Valley-type models worldwide. Furthermore, it demonstrates the potential of in situ U-Pb calcite geochronology to date ore deposits lacking syn-ore minerals suitable for traditional dating methods.
As a tectonic window into the Lesser Himachal Himalaya, India, a group of metasediments and gneissic rocks, known as the Jutogh Group and Wangtu Gneissic Complex (WGC), occurs near the Jhakri thrust to the west and Wangtu to the east. In the Jutogh Group, chlorite-mica schist, garnet-staurolite schist and sillimanite-schist develop successively. The formation of chemically zoned garnet, which destabilized low-temperature assemblages, is predicted to be at 550–650 °C and 0.8–0.9 GPa by phase equilibria modelling. The retrograde segment consists of exhumation and cooling, yielding a tight clockwise P–T path. Moreover, textural observations and in-situ U-Th-Pb chemical dating indicate that metasedimentary rocks contain Cambrian monazites. These monazites have ages that cluster around 500 Ma. The ƐNd[1.8Ga] of Jutogh rocks ranges from − 1.0 to -8.1, with depleted mantle-model ages between 3.07 and 2.25 Ga. The garnet core and its leachates yield an Sm-Nd isochron age of 472 Ma. Another Sm-Nd isochron age of 454 Ma is obtained from biotite, garnet rim, and garnet rim leachate. According to phase equilibrium modelling, Sm-Nd dating, and monazite geochronology, the Jutogh Group experienced metamorphism along the northeast margin of Gondwana during the Cambro-Ordovician accretion.
Here we present a detailed investigation of the tectono-metamorphic history of the two-pyroxene mafic granulite located in the southern region of the Sonapahar area. This involves conducting monazite chemical dating, analyzing petrological and geochemical characteristics, applying geothermobarometry, performing phase equilibria modeling, and tracing a pressure-temperature (P-T) path.
Wegener's Continental Drift Theory has laid the foundations of modern plate tectonics. However, despite decades of work and studies around the globe, modern plate tectonics still does not explain all the datasets acquired up to now and is well overdue for a major update. We propose a new theory, the orogenic bridge theory, which partly builds on the Continental Drift Theory and modern plate tectonics and reconciles them with the idea put forward by a competing theory, the Land Bridge Theory (or Isthmian Links). The orogenic bridge theory states that the style of continental rifting is directly controlled by preexisting orogenic structures. On the one hand, preexisting orogens trending parallel to an opening rift facilitate breakup and rift propagation and control the strike and geometry of rift-related structures. This endmember has already been broadly studied worldwide. On the other hand, orogens oriented orthogonal (or highly oblique) to the opening rift will act as strong barriers forcing the rift to step, therefore delaying or impeding breakup and rift propagation and localizing the formation of major-offset transform faults. In the present contribution, we review the evidence in favor of a correlation between rift-orthogonal orogens and major transforms and discuss some of the main implications of the orogenic bridge theory.
Granitic batholiths of the ∼500 Ma Ross Orogen in Antarctica are voluminous in scale, reflecting prolific magmatism along the active early Paleozoic convergent margin of Gondwana. New age and isotopic analysis of zircons from a large suite of Ross granitoids spanning >2,000 km along the orogen provide a wealth of geochronologic, tracer, and inheritance information, enabling us to investigate the pace of magmatism, along‐strike temporal and geochemical trends, magmatic sources, and tectonic modes of convergence. Because granitoids penetrate the crust of the earlier Neoproterozoic rift margin, they also provide insight into the age and composition of the largely ice‐covered East Antarctic craton. Zircon U‐Pb ages from these and other samples indicate that active Ross magmatism spanned 475–590 Ma, much longer than generally regarded. Most samples have heavy zircon δ¹⁸O values between 6.5 and 11.5‰ and initial εHf compositions between 0 and −15; their isotopic co‐variations are independent of age, as in other contemporary continental arcs, and reflect largely crustal melt sources. Samples near Shackleton Glacier have distinctly more mantle‐like isotope composition (i.e., radiogenic εHf and low δ¹⁸O) and separate two regions with distinctive isotopic properties and inheritance patterns—a more juvenile section of Mesoproterozoic crust underlying the southern TAM and an older, more evolved region of Paleoproterozoic and Archean crust in the central TAM. The isotopic discontinuity separating these regions indicates the presence of a cryptic crustal boundary of Grenvillian or younger age within the East Antarctic shield that may be traceable into the western Laurentian part of the Rodinia supercontinent.
Reliable reconstruction of global paleogeography through deep geologic time provides a key surface boundary condition for investigating many first-order Earth system and geodynamic processes such as climate change, geomagnetic field stability, regional geological and tectonic history, and biological evolution. Over the past decade, the development of the GPlates software led to a resurgence of community efforts in creating state-of-the-art plate tectonic models that integrate paleomagnetic, geological, and paleontological datasets, resulting in a plethora of reconstruction models. In this paper, we briefly review the strengths and weaknesses of existing global models, which depict alternative and sometimes contradictory tectonic scenarios. We then provide an overview of the general procedure in our construction of a revised Phanerozoic global paleogeographic model, including (1) evaluation of the paleomagnetic data that quantitatively dictate continental paleolatitudes and orientations, (2) selection of reference frames in which continents were positioned, and (3) calibration of continental longitudes in deep time. We update the apparent polar wander paths (APWPs) of the major continents using a recently developed weighted running mean approach, which rectifies two major issues with the conventional running mean approach regarding missing paleopoles in age windows and the enforced assumption of the Fisherian distribution. We re-evaluate the Phanerozoic continental reconstructions in a paleomagnetic framework using the updated APWPs, and calibrate continental paleolongitudes following the extended orthoversion hypothesis by placing the centroids of supercontinents Rodinia and Pangea 90◦ _apart, with that of Rodinia at ~90◦E. We emphasize that the resulting global model is not intended to provide solutions to all global tectonic issues throughout the entire Phanerozoic Eon. Rather, we present our results as one viable model of Phanerozoic tectonic history which, like many existing interpretations, is built upon our understanding of the paleomagnetic, geological, and paleontological observations. Our goals are for this study to highlight the fundamental differences between reconstruction models and to serve as a starting point for future studies to fill key data gaps and test alternative hypotheses and tectonic scenarios.
The Lesser Qinling area is the largest outcrop of the Precambrian basement in the southern margin of the NorthChina Craton (S-NCC). Notably, many carbonatite-related polymetallic deposits are distributed in this area,including the Jialu deposit with light and heavy REE mineralization. Carbonatite and granite from the Jialudeposit contain diverse monazite and zircon grains, and deciphering the age distributions and chemical com-positions of these monazites and zircons is crucial for comprehending the multi-stage magmatic and meta-morphic events in the S-NCC. Type I monazite from banded REE ore veins yields a U-Pb age of 217.0 ± 5.0 Ma,representing the formation age of carbonatite. Type II monazite from granite yields consistent U-Pb and Sm-Ndages of ~1.95 Ga, representing the emplacement age of granite. Type III monazite is hydrothermal in origin, andyields two dominant age peaks at ~550 Ma and ~525 Ma. Types I, II and III zircons are xenocrysts from theTaihua Group and yield two main age peaks at ~2.35 and ~2.17 Ga. Of note, type III zircon also records an earlyPaleozoic tectonothermal event by a lower intercept age of 532 ± 59 Ma, which overlaps the ages recorded byhydrothermal monazite. The early Paleozoic tectonothermal events discovered may be a manifestation of theglobal Pan-African Orogeny in the S-NCC. This new finding further implies that the S-NCC was significantlyaffected by the assembly of the Gondwana supercontinent during the early Paleozoic.
The landscape of the northern part of Jodhpur located in western Rajasthan, India is endowed with a wide variety of volcanic and sedimentary type geoheritage of global signifcance. These are represented by rocks of Malani Igneous Suite (MIS)
of Cryogenian age forming basement for overlying Ediacaran Jodhpur Group (JG) of Marwar Supergroup (MSG). Unique and rare volcanic features of MIS and its interface with the sandstone of JG have been declared as the National Geologi�cal Monuments of India. The site-specifc landscape of the Soorsagar Formation (SSF) of JG covering about 54 sq. km area in the northern rural part of Jodhpur provides an outstanding record of seven types of geoheritage. Among these, the most signifcant sedimentary and paleontological geoheritage is represented by a treasure of sedimentary structures and a rich assemblage of Ediacaran fossils of marine paleo-ecosystem. Such records of past tectonics, climate, paleogeography,
paleoecology, and environments showcasing 200 million years of Earth’s history characterize the land-sea interaction and distribution in this part of Eastern Gondwana land. Thus, it displays global geodiversity of both intrinsic and extrinsic geo�heritage values that provide eminent narratives for geo-education and geotourism. However, the unique geoheritage of the SSF landscape is under great threat to degradation and damage dominantly due to anthropological activities. To study such threats and damage, a study is conducted using various geological and remote sensing techniques. Interpretation of satellite images of about ffty years reveals that dominantly sandstone mining along with urbanization activities is responsible for damaging the signifcant geoheritage of SSF. The present paper embodies geoheritage characterization and assessment of the landscape of SSF with its progressive damage to understand the necessity for its conservation through protected status by Geopark creation in the northern rural part of Jodhpur.
There is a consensus that volcanism along the East African Rift System (EARS) is related to plume activities. However, because of our limited knowledge of the local lithospheric mantle, the dynamics of the plume are poorly constrained by magma chemistry. The Turkana Basin is one of the best places to study plume‐related volcanism because the lithospheric mantle there is unusually thin. New Ar‐Ar geochronology and geochemical data on lavas from western Turkana show that Eocene volcanics have relatively low ²⁰⁶Pb/²⁰⁴Pb (<19.1) and high εNd (>3.78). Their relatively high Ba/Rb (35–78) ratios suggest contributions from the shallow lithospheric mantle. Oligo‐Miocene Turkana volcanics have HIMU‐ and EMI‐ type enriched mantle signatures with overall lower Ba/Rb ratios, which is consistent with partial melting of plume material. Pliocene and younger Turkana volcanics have low Ba/Rb and Sr‐Nd‐Pb isotope ratios that resemble those of Ethiopian volcanics with elevated ³He/⁴He ratios. This temporal variation can be reconciled with a layered plume model where an outer layer of ancient recycled oceanic crust and sediment overlies more primitive lower mantle material. Beneath Ethiopia, the outer layer of the plume is either missing or punctured by the delamination of the thicker overlying lithospheric mantle at ca. 30 Ma, an event that would have facilitated the rapid upwelling of the inner portion of the plume and triggered the Ethiopian flood volcanism. The outer layer of the plume may be thicker in the southern EARS, which could explain the occurrence of young HIMU‐ and EMI‐type volcanics with primordial noble gas signatures.
The Sør Rondane Mountains (SRM) in East Antarctica, lie within the late Neoproterozoic–early Paleozoic collision zone between East and West Gondwana. Many studies have been carried out in the eastern SRM, whereas fundamental questions on the western SRM remain unanswered, for example, tectonic division and detailed metamorphic age. This paper describes zircon U–Pb ages from gneisses in the western SRM, and the tectonic division of this area is discussed.
The rocks of the study area are divided into units 1 to 3 based on their lithology and structural position. Units 1 and 2, which are divided by the Kanino–tume shear zone (KSZ), are mainly composed of greenschist/amphibolite–facies gneisses and amphibolite/granulite–facies gneisses, respectively. Unit 3 is mostly occupied by the Proterozoic GTTG. It is, in this study, revealed that the metamorphic ages of units 1 and 2 are, respectively, ca. 600–550 Ma and ca. 670–600 Ma. The distribution of the KSZ has been inferred by mapping, but the present results on the distribution of metamorphic ages confirm this. The KSZ of the low–angle shear zone may be a critical tectonic boundary dividing the two gneiss units of ca. 600–550 Ma and ca. 670–600 Ma within the East African–Antarctic orogen.
Prior to the Grenvillian continentcontinent collision at about 1.0 Ga, the southern margin of Laurentia was a long-lived convergent margin that extended from Greenland to southern California. The truncation of these 1.8-1.0 Ga orogenic belts in southwestern and northeastern Laurentia suggests that they once extended farther. We propose that Australia contains the continuation of these belts to the southwest and that Baltica was the continuation to the northeast. The combined orogenic system was comparable in length to the modern American Cordilleran or Alpine-Himalayan systems. This plate reconstruction of the Proterozoic supercontinent Rodinia called AUSWUS (Australia-Southwest U.S.) differs from the well-known SWEAT (Southwest U.S.-East Antarctic) reconstruction in that Australia, rather than northern Canada, is adjacent to the southwestern United States. The AUSWUS reconstruction is supported by a distinctive "fingerprint" of geologic similarities and tectonic histories between Australia and the southwestern United States from 1.8 to 0.8 Ga, and by a better agreement between 1.45 and 1.0 Ga paleomagnetic poles for Australia and Laurentia.
Two monazite grains occurring as inclusions within garnet in a granulite facies metapelite from Chittikara, within the Kerala Khondalite Belt in southern India, were analysed for U, Th and total Pb, employing a precise electron microprobe. Within a single monazite grain, concentrations range from 4.88 to 6.89 wt percent for ThO2, 0.508 to 0.948 wt percent for UO2 and 0.194 to 0.665 wt percent for PbO. Ages were calculated from each electron microprobe analysis and we could distinguish different ages for the core and rim of individual monazite grains. The ages obtained range from ca 2000 to 1700 Ma for the core, and ca 590 to 520 Ma for the rim. This study indicates that the monazite grains preserved their relict cores with older ages through the resetting and overgrowth of younger rims. The resetting and overgrowth of monazite are considered to have taken place at around 590-520 Ma, most possibly during the Pan-African tectonothermal event which is manifested in the East Gondwanaland crustal fragments surrounding South India.
A major alkali province of late Panafrican age occupies central Madagascar and takes the form of a thick sequence of ‘stratoid’(sheet-like)
granites emplaced in a mid-crustal gneissic basement This alkaline magmatism has been interpreted as a consequence of extensional
tectonics accompanying the collapse of the Mozambique belt. The rocks belong to three petrographic types: subsolvus granites,
hypersolvus alkaline granites and syenites. Major and trace element analyses have typical A-type characteristics. Two distinct
magmatic suites are recognized: a mildly alkaline suite including all the subsolvus granites and a strongly alkaline suite
including the hypersolvus alkaline granites and the syenites. We propose that the mildly alkaline suite was derived from a
granodioritic crustal protolith. Some of the strongly alkaline granites and the quartz syenites display low δ18O isotopic signatures of around +6‰.The parental magmas for this suite are most probably of mantle derivation. The more evolved
compositions are consistent with crystal fractionation processes. Contemporaneous alkaline silicicplutonism occurs in many
parts of the Panafrican belt of Eastern Africa; however, sheet-like intrusions have rarely been described. As a large-scale
province, the nearest analogues of the stratoid granites of Madagascar are the rapakivi granites of earlier Proterozoic age
in Scandinavia and Greenland.
Lead, uranium and thorium can be analyzed with precision in monazite using the electron microprobe. The concentrations can be interpreted directly as an age with a typical precision of ±30 Ma for a 300 Ma age and ± 100 Ma for a 3.0 Ga age. For samples of known age, the discrepancy between the microprobe age and the isotopic age is less than the errors. This method is an in situ dating technique, which can be used to date domains at the microscopic scale, with a spatial resolution of a few microns. The first results indicate that, as for zircon, monazite can display age heterogeneity, preserving old domains in a more recent crystal. There is an abridged English version. -English summary
We present new palaeomagnetic and isotopic data from the southern Victoria Land region of the Transantarctic Mountains in East Antarctica that constrain the palaeogeographic position of this region during the Late Cambrian and Early Ordovician. A new pole has been determined from a dioritic intrusion at Killer Ridge (Ar-40/Ar-39 biotite age of 499 +/- 3 Ma) and hornblende diorite dykes at Mt. Loke (21 degrees E, 7 degrees S, A95 = 8 degrees, N = 6 VGPs). The new Killer Ridge/Mt. Loke pole is indistinguishable from Gondwana Late Cambrian and Early Ordovician poles. Previously reported palaeomagnetic poles from southern Victoria Land have new isotopic age constraints that place them in the Late Cambrian rather than the Early Ordovician. Based upon the new palaeomagnetic and isotopic data, new Gondwana Late Cambrian and Early Ordovician mean poles have been calculated.
The Chewore Inliers are isolated outcrops of the Zambezi Mobile Belt within the Mesozoic Lower Zambezi Rift Valley in Zimbabwe. Detailed mapping has recognized four terranes: the Zambezi, Quartzite, Granulite and Ophiolite Terranes. Apart from the Ophiolite Terrane, all are dominated by supracrustal gneisses with concordant granitic orthogneiss units of 1071 ± 8 and 1083 ± 8 Ma age. These terranes experienced low-P-high-T metamorphism (M1) terminated by isobaric cooling at 945 ± 34 Ma. M1 assemblages of sillimanite-spinel-garnet, garnet-orthopyroxene and two-pyroxene mafics are recorded in the Granulite Terrane, and conditions of formation were 4.4 ± 1.7 kbar and <800°C. M1 mineral parageneses and associated ductile deformation structures dominate the Granulite Terrane, but M1 mineral parageneses are only preserved as sillimanite-spinel inclusions in garnet cores in the other terranes. The Zambezi, Quartzite and Ophiolite Terranes were almost totally recrystallized during reworking in the M2 metamorphic cycle. M2 metamorphism accompanied NE over SW directed transport during Pan-African orogenesis of the Zambezi Belt at 524 ± 16 Ma. Average peak MI2 conditions, calculated using THERMOCALC V2.0b, were 7.9-8.6 kbar and 590 ± 95°C, 630 ± 95°C and 717 ± 95°C from the south and north Zambezi Terranes and Quartzite Terrane, respectively M2 involved a clockwise P-T path from the chloritoid stability field with matrix assemblages crystallized in the kyanite-staurolite field or at the kyanite-sillimanite transition, and near-isothermal decompression occurred through the peak of metamorphism into the sillimanite field. In contrast, the Granulite Terrane was incorporated within the Zambezi Belt as a thrust-bound slab and experienced only minor structural reworking during M2. Granulite Terrane samples with 2 km of the basal thrust margin preserve M1 mineral assemblages but these minerals were chemically re-equilibrated without recrystallization during M2 at conditions of 5.6 ± 1.5 kbar and 631 ± 100°C. Granulite Terrane samples were totally recrystallized in shear zones at the margin of this terrane. These samples equilibrated at conditions identical to the peak of M2 at 7.7 ± 1.9 kbar and 590 ± 110°C. The re-equilibrated and recrystallized sample sets define two points on the clockwise P-T path experienced by the Granulite Terrane during further burial and reworking in the Pan-African Orogeny, and are consistent with the M2 P-T path documented for the other terranes.
The doleritic dike of Mt. Timna intrudes relatively homogeneous alkali granite that
was previously fractured and intruded by rhyolitic, andesitic, and andesitic-rhyolitic
composite dikes. The doleritic dike directly underlies the sandstone of the Amudei
Shelomo Formation of Early Cambrian age. The sandstones do not exhibit any sign of
contact metamorphism. Similar doleritic dikes were found intruding the Neoproterozoic
volcanic rocks of Mt. Amram, 13 km south of Mt. Timna. Radiometric dating
of the doleritic dikes using the K-Ar method yielded a mean age of 546.3 ± 10.1 Ma
for Mt. Timna (two samples) and 508.9 ± 9.2 Ma for a sample at Mt. Amram. An 4°Ar/
39 Ar plateau age of 531.7 ± 4.6 Ma represents 67% of the 39 Ar that was released during
the analysis. This is the best estimate for the formation age of the doleritic dike at Mt.
Timna. Since the dikes intruded the youngest Precambrian units and did not affect
overlying Cambrian sediments, they represent the youngest magmatic event in the
crystalline basement of the northern part of the Arabian-Nubian Shield and are of
Cambrian age.
New U-Pb zircon ages and Sm-Nd and Rls-Sr isotopic data are presented for orthogneisses from north-central Madagascar, including Ile Sainte Marie, Alaotra-Beforona, Maevatanana, and Ambatolampy-Ambatomarina. A migmatite tonalite gneiss from Ile Sainte Marie is dated precisely at 3187 +/- 2 Ma and has a Sm-Nd model age (T-DM) of 3204 Ma, thereby establishing a Middle Archean age for the oldest, juvenile gneisses in northeast Madagascar. Dated orthogneisses, intrusive into the schist/paragneiss sequences, range in age between 2522 and 2494 Ma and have Sm-Nd model ages (T-DM) between 3207 Ma and 2541 Ma. These data establish a Late Archean or older age for two of the schist/paragneiss sequences of Madagascar and suggest that the cratonal regions of north-central Madagascar and south India were once contiguous. Strontium and neodymium isotopic data from the Late Archean rocks are interpreted to reflect mixing between depleted mantle magmas and evolving Middle Archean crust. U-Pb geochronology of other plutonic igneous rocks demonstrates that the Middle Neoproterozoic (800-640 Ma) represents an important period of igneous activity throughout north-central Madagascar. In addition, a latest Neoproterozoic-Early Cambrian (580-520 Ma) period of high-grade metamorphism and intrusive igneous activity is recorded in western and central parts of north Madagascar. We attribute this later activity to the effects of continental collision between East and West Gondwana.
The Heimefrontfjella mountains, Western Dronning Maud Land (East Antarctica), are dominantly composed of Grenville-aged (≈ 1.1 Ga) rocks, which were reworked during the Pan -African orogeny at ≈500 Ma. Three discontinuity-bounded Grenville-aged terranes have been recognized namely (from north to south) the Kottas, Sivorg and Vardeklettane terranes. The terranes contain their own characteristic lithological assemblages, although each is made up of an early supracrustal sequence of metavolcanic and/or metasedimentary gneisses, intruded by various (predominantly granitoid) suites. No older basement upon which the protoliths of these older gneisses were deposited has been recognized. In each terrane the older layered gneisses were intruded by various plutonic suites ranging in age from ≈ 1150 to ≈1000 Ma. The Vardeklettane terrane is characterized by abundant charnockites and two-pyroxene granulite facies parageneses in metabasites, whereas the Sivorg and Kottas terranes were metamorphosed to amphibolite facies grade. P-T estimates show that peak metamorphic conditions changed from ≈600°C at 8 kbar in the south, to ≈700 °C at 4 kbar in the northern Sivorg terrane. Regional greenschist retrogression of high-grade assemblages may be of Pan-African age. The Heimefrontfjella terranes were juxtaposed and pervasively deformed during a complex and protracted period of E-W collision orogenesis in a transpressive regime at ≈ 1.1 Ga. This is manifest as early, gently dipping thrust-related shear fabrics (D1), succeeded by the initiation of an important (D2) steep dextral shear zone (Heimefront shear zone, HSZ), during which the early fabrics and structures were steepened and rotated in an anticlockwise sense. The HSZ is a curvilinear structure which changes from a dextral oblique strike-slip lateral ramp in the north to a steep dip-slip frontal ramp in the south, where it forms the boundary between the Sivorg and Vardeklettane terranes. The Pan-African event is manifested as discrete, low- to medium-temperature ductile to brittle shears (D3) and numerous K/Ar cooling ages.
Southern Madagascar comprises a complex Precambrian terrain of high-grade metamorphic rocks with a history of polyphase deformation and metamorphism. Two prominent N-S trending late Neoproterozoic ductile shear zones, the Ampanihy and Vorokafotra shears, each with projected strike length of >450 km and between 10 and 20 km in width, crosscut the region. A third set of en echelon shears forms part of the early Paleozoic Ranotsara Shear Zone that cuts the basement in a NW-SE direction over a combined strike length of >400 km. The host rocks of these shears comprise paragneisses (metasediments) with detrital zircons ranging in age between 720 and 1900 Ma. A felsic layer, interpreted as a metavolcanic rock, gives a date of 722+/-1Ma. Remnants of late Archean orthogneisses in the central part of the study area may represent basement to the paragneisses. Four episodes of deformation and metamorphism have been recognized on the combined basis of field observations, petrogenesis, and U/Pb analyzes of zircons, monazites, sphenes, and rutiles. Two episodes of early simple shear deformation (D1 and D2) at midcrustal levels occurred between 627 and 647 Ma, during which northeast verging recumbent sheath folds and ductile thrusts were formed and peak prograde metamorphism reached 7-12 kbar at 750°-900°C. Early prolate mineral fabrics (L1/L2) are preserved in massif-type anorthosite bodies and their marginal country rocks. D1 occurred between 630 and 647 Ma, while D2 occurred at 627-628 Ma. This was followed by a 10-15 Myr period of static, annealing metamorphism until 609-614 Ma when bulk shortening (D3) took place. D2 and D3 are coaxial but are separated in time by leucocratic dykes that intruded between 610 and 620 Ma. D3 was focused zonally, forming the prominent N-S shear zones between 607 and 609 Ma; its oblate strain resulted in a strong composite D2/D3 fabric defined by subvertical S-tectonites and subhorizontal intersection lineations. A variety of post-D3 pegmatites accompanied ~85 Myr of relatively static annealing and metasomatic/metamorphic mineral growth, during which numerous occurrences of phlogopite, uranium, and rare earth elements formed. A continuum of concordant monazite dates suggests that this thermal event is part of an extended period of low-pressure (3-5 kbar) charnockite-producing processes between 520 and 605 Ma. The continuum, however, appears to be punctuated at ~580, 550, and 520 Ma. Deformation (D4) recorded within the Ranotsara Shear Zone overlaps with the youngest parts of the regional metamorphic conditions between 520 and 550 Ma. Prevailing low-pressure, high-temperature amphibolite-granulite facies rapidly gave way to greenschist facies conditions between 490 and 530 Ma, as is evident from overlapping ages of zircon, monazite, sphene, and rutile. We conclude that D1 to D3 represents a period of 40 Myr of compressional deformation that we interpret to be related to collisional events during the amalgamation of Gondwana. The first part of the thermal continuum between 550 and 605 Ma reflects ~55 Myr of slow cooling and annealing at midcrustal levels, while the onset of the last episode, between 520 and 530 Ma, heralds accelerated exhumation accompanied by extensional tectonics between 490 and 520 Ma. We believe that this postcollisional time span represents a prolonged period of evolution of a Tibetan-style plateau into an Aegean-style extensional terrain. This ~100 Myr event in southern Madagascar is similar to that recorded throughout large sectors of the East African Orogen between ca. 500 and 600 Ma. We believe that this type of postconvergent thermotectonism best represents the original definition of ``Pan-African'' [Kennedy, 1964], which in today's terminology equates with ``postorogenic extensional collapse'' [Dewey, 1988], or ``destabilization of an orogen'' [Lipps, 1998]. Kennedy's Pan-African was widespread throughout the interior a supercontinent, when Gondwana's periferal margins were subjected to far-field tensional forces. This suggests that neither gravitational collapse of the Pan-African-Braziliano Orogens nor delamination were the sole or even the dominant driving forces for the postconvergent extension.
In this classic series-generating paleontology/geology book published by Columbia University Press, Mark and Dianna McMenamin explore the evolutionary and paleoecological questions associated with the Cambrian Explosion. This book both names and maps the initial paleogeographic reconstruction of the billion year old supercontinent Rodinia. The observations and interpretations in this book, particularly as regards the timing of the Cambrian Explosion, have stood the test of time. The issues identified herein as most important for understanding the Proterozoic-Cambrian transition, remain so today.
The Precambrian of Madagascar is divided into two sectors by the north-west trending sinistral Ranotsara shear zone, which continues in the Mozambique belt, probably as the Surma shear zone, and in Southern India as the Achankovil shear zone. South of Ranotsara six north-south trending tectonic belts are recognized that consist largely of granulite and high amphibolite facies paragneisses, phlogopite diopsidites, concordant granites and granulites. North of Ranotsara the central-northern segment is traversed by a north-trending axial 100-150 km wide dextral shear zone of probable Pan-African age, which was metamorphosed under granulite and high amphibolite facies conditions and which has reworked older basement. This shear zone continues across southern India as the Palghat-Cauvery shear zone. Major stratiform basic -ultrabasic complexes occur in the axial zone and in the basement to the west. Well preserved low grade continental margin-type sediments (quartzites, mica schists and stromatolitic marbles) of Kibaran age are present in western Madagascar. Two partly greenschist grade sedimentary groups lie unconformably on high grade basement in north-east Madagascar. Isotopic age data suggest the presence in Madagascar of Archaean, Early and Mid-Proterozoic crustal material that was extensively reworked in Pan-African times.
The Bunger Hills area, which forms part of the East Antarctic Shield, consists predominantly of granulite-facies orthogneiss with subordinate mafic granulite and garnet, sillimanite, and cordierite-bearing paragneiss. The igneous precursors of granodioritic orthogneiss crystallised about 1500-1700 Ma ago, whereas late Archaean (2640 Ma) tonalitic orthogneiss occurs in the Obruchev Hills, in the southwest of the area. Metamorphism reached a peak of about 750-800°C and 5-6 kb (M 1) 1190 ± 15 Ma ago and was accompanied by the first of three ductile deformation events (D 1). Voluminous, mainly mantle-derived plutonic rocks were emplaced between 1170 (during D 3) and 1150 Ma. Abundant dolerite dykes, of at least four chemically distinct groups, were intruded at about 1140 Ma. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism in both areas was the result of continental collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield. Exposures west of the Denman Glacier are also mainly granulite-facies gneiss, intruded by a variety of mafic to felsic plutonic rocks. They differ from the Bunger Hills in being partly derived from Archaean protoliths (~3000 Ma), in lacking isotopic evidence for a Mesoproterozoic high-grade event, and in not being intruded by dolerite dyke swarms. -from Authors
The Pan-African Zambezi belt forms part of a Late Proterozoic orogenic system transecting southern Africa. Rifting to form the Zambezi supracrustal basin occurred at ca. 880 Ma. Orogenesis is dated at ca. 820 Ma, based on several isotopic ages from Zambia and Zimbabwe, including an igneous age for a syntectonic batholith injected into a transcurrent shear zone within the belt in Zambia. This shows that deformation in the Zambezi belt is nearly 200 Ma older than in the Damara belt along strike in Namibia, precluding synchronous closure of a single ocean basin along the Dmara-Zambezi trends. An older, Middle Proterozoic orogenic province can be traced across the Zambezi belt, suggesting that the belt evolved as an intracontinental rift or narrow ocean basin with limited displacement of terranes on each side. This in turn implies that this portion of Gondwana was assembled before development of the Zambezi belt and was affected primarily by intraplate deformation during the Pan-African event. -from Authors
The continuous operation of the plate-tectonic Wilson Cycle over the greater part of Earth history has probably led to the episodic disruption and re-assembly of the continental fragments into a large number of different mosaical configurations at different times. This review raises 3 specific possibilities: 1) Eastern N America was rifted from western S America in latest Proterozoic-earliest Paleozoic times before its subsequent collision with NW Africa; 2) SW Africa (Kalahari craton) was rifted from western N America during the late Proterozoic, prior to its later collision with the Congo craton at about 550 Ma; 3) the Archaean Pilbara craton of Australia was rifted from the W Kaapvaal craton at some time in the early to middle Proterozoic, between 2000 and 1400 Ma. -from Author
Palaeomagnetic properties from a series of mainly rhyolitic lava flows from the Malani volcanic suite in Rajasthan-India, dated at 745 ± 10 my, were studied by means of alternating fields and thermal demagnetization methods.
The mean direction of the characteristic magnetization component, of both normal and reversed polarity: D = 354.5̊, I = +53.5̊, a95 = 8̊, N = 10, (Pole: 80.5̊ N, 43.5̊ E, dp = 8̊, dm = 11.5̊) is in good agreement with earlier results obtained by Athavale et al. (1963). The fold test gives a positive result and the above mentioned mean direction from the Malani rhyolites is in agreement with other Precambrian data from the Indian subcontinent. Therefore, this mean direction is interpreted to represent the primary magnetization direction. The position and orientation of the Indian subcontinent about 745 my ago was more or less alike its present-day orientation, however, at the time India was situated at a slightly higher latitude.
Evidence supports the hypothesis that the Laurentian and East Antarctic-Australian cratons were continuous in the late Precambrian and that their Pacific margins formed as a conjugate rift pair. A geometrically acceptable computer-generated reconstruction for the latest Precambrian juxtaposes and aligns the Grenville front that is truncated at the Pacific margin of Laurentia and a closely comparable tectonic boundary in East Antarctica that is truncated along the Weddell Sea margin. Geologic and paleomagnetic evidence also suggests that the Atlantic margin of Laurentia rifted from the proto-Andean margin of South America in earliest Cambrian time. -from Author
Laurentia, the Precambrian core of the North American Continent, is surrounded by late Precambrian rift systems. Within the supercontinent of Pangea, North America therefore constitutes a "suspect terrane' because its origin as a discrete continent and geographic location prior to the late Paleozoic are uncertain. A geometric and geologic fit can be achieved between the Atlantic margin of Laurentia and the Pacific margin of the Gondwana craton. In the reconstruction, the ca. 1.0 Ga Grenville belt continues beneath the ensialic Andes of the present day to join up with the 1.3-1.0 Ga San Ignacio and Sonsas-Aguapei orogens of the Transamazonian craton. The fit supports and refines suggestions that Laurentia broke out from between East Antarctica-Australia and embryonic South America during the Neoproterozoic, prior to the opening of the Pacific Ocean basin and amalgamation of the Gondwana supercontinent. This implies that there may have been two supercontinents during the Neoproterozoic, before and after opening of the Pacific Ocean. -from Author
Shortening and thickening of continental lithosphere cause an increase in surface elevation, a decrease in the thermal gradient and, unless the crust is initially quite thick, a decrease in potential energy with respect to a mid-ocean-ridge lithospheric column. Continental convergence could therefore be self-sustaining. The lower part of the lithosphere is probably removed intermittently by convection. Convective removal of the lithospheric root below regions of continental convergence will cause a rapid increase in surface elevation and potential energy and create a step in the geotherm. The large excess in potential energy with respect to its surroundings may result in indefinite extension of the continental column. Extension of lithosphere immediately following convective removal of the root will decrease the thermal time constant for decay of the step in the geotherm, allowing a transient heating event to affect the crust. -from Authors
High grade orthogneiss, amphibolitic dykes and paraschist to migmatites were studied in the Red Sea Lowlands ofeastern Eritrea. Chemical data and a mineral assemblage of kyanite, staurolite, almandine garnet, biotite and quartz indicate that the schists were formed by metamorphism of pelitic metasediments derived by subaerial weathering,deposited in a marine environment. Thermobarometry based on element partitioning between coexisting minerals ofschist, orthogneiss and amphibolite shows that peak metamorphic conditions were ca 700°C and 8-10 kbar. An overall clockwise PT loop is suggested by the thermobarometry results, and is consistent with a collision setting. TheEritrean high-grade metasediments can be correlated with similar rocks between Arabia and this defines a sedimentarybasin that was at least 400 km from north to south. Low initial 87Sr/86Sr (0.7014 0.7028) and eNd~8oo M~ of +2.5 to+4.7 along with a mean ToM model age of 1.05 Ga indicates that juvenile Neoproterozoic crustal sources controlled the sedimentation of the pelites, and permits negligible involvement of older crustal sources. Rb/Sr geochronology suggests an age of ca 650 Ma for thermal resetting, consistent with a model whereby plate collision between east and west Gondwanaland was responsible for the metamorphism and exhumation. These metasediments reflect the transition between the northern and southern sectors of the East African Orogen, containing the juvenile isotopic signature similar to rocks of the Arabian Nubian Shield but a chemical composition and metamorphic grade that are
indistinguishable from assemblages characteristic of the Mozambique Belt.
We report new neodymium and strontium isotopic data for two Proterozoic carbonatites and related alkalic rocks, at Hogenakal and Sevathur in southern India. These complexes were emplaced into the crust at 2.4 Ga (Hogenakal) and 0.77 Ga (Sevathur). Their initial strontium and neodymium isotopic compositions, together with oxygen isotope data, suggest the involvement of a single long-lived enriched mantle source in their origin. The isotopic evolution of this source indicates that it formed approximately contemporaneously with the accretion and metamorphism of the overlying crust at the southern margin of the Dharwar craton and survived convective disruption in the mantle from early Proterozoic until at least 770 Ma ago. The older of the two carbonatites was intruded into young crust that was not older than about 150 Ma at the time of emplacement. The isotopic data contrast with those from carbonatites of the Canadian Shield, for which isotopic evidence also suggests origin from a long-lived lithospheric source, but one with a depleted chemical signature. They, therefore, indicate that there is no geochemically unique lithospheric source for carbonatites.
Geochemical and isotope data for granitoid rocks from southern and eastern Ethiopia delineate the presumed margin of the Pan-African juvenile terrain of the Arabian-Nubian Shield against an older crustal segment of unknown origin extending from eastern Ethiopia to northern Somalia. Granitoids from southern Ethiopia have higher Na2O and and lower Cr and Ni than granitoids with comparable SiO2 values from eastern Ethiopia. In southern Ethiopia three periods of magmatism are identified on the basis on single zircon evaporation ages, namely at ∼850, ∼750-700 and ∼650-550 Ma, and these correlate well with events documented from other parts of Ethiopia and the Arabian-Nubian Shield. The initial ϵNd(700 Ma) and ϵsr(700 Ma) values range from −1.2 to +3.2 and from −13.4 to + 3.7, respectively, which precludes any significant contribution from much older continental crust in the generation of these rocks. Neodymium mean crustal residence ages, based on a depleted mantle model, range from 0.96 to 1.26 Ga. These data support the interpretation that southern Ethiopia constitutes part of the Arabian-Nubian Shield. In contrast, granitoids from eastern Ethiopia show geochemical features of S-type granites. In eastern Ethiopia Pal aeo-Neoproterozoic zircon ages (781–2489 Ma) are found. Initial ϵNd(700 Ma) and ϵsr(700 Ma) values range from−4.3 to −18.3 and + 33.3 to + 99.8, respectively. Neodymium mean crustal residence ages range from 1.62 to 2.88 Ga. These data, in comparison to the western and southern parts of Ethiopia, are indicative of considerable reworking of pre-Pan-African crust.
We attempted to obtain the magmatic crystallization age of a metamorphosed (granulite facies, T = 800 ± 90°C; P = 8 ± 1 kbar) massif-type anorthosite from the Ankafotia body of southwest Madagascar. The sample studied is a coarse-grained leuconorite with good preservation of igneous texture and mineralogy, although plagioclase, which contains abundant rutile and zircon inclusions, has been slightly recrystallized. Thirty three isotope dilution U-Pb analyses of zircons representing single-grain fragments (29 analyses) and multi-grain fractions (4 analyses) yield a spectrum of concordant ages from 631 to 549 Ma, a time span of more than 80 myr. Back-scattered electron and cathodoluminescence images show that most grains are either homogeneous, structureless fragments (35%), or are permeated to a variable degree by anastamosing cracks occupied by relatively U- and/or Th-enriched zircon (45%); a smaller percentage of grains show relict magmatic zoning (20%). Thin, U- and/or Th-rich overgrowths occur on about 25% of grains. Raman spot analyses demonstrate that all fragments are highly crystalline and non-metamict. There are marked correlations between zircon grain size and internal features, such that the oldest grains are larger, and show relict magmatic zoning; the youngest grains are small fragments containing high-U crack networks. Ion microprobe spot analyses show that each zircon grain preserves a distinct trace element signature; rare earth element patterns show heavy REE-enrichment, with negative Eu anomalies and positive Ce anomalies. We suggest that the ca. 80 myr spread in concordant U-Pb ages in this sample is indicative of high-temperature Pb-loss during one or more protracted periods of granulite facies metamorphism, with only minor episodic or continuous metamorphic zircon growth. Volume diffusion and/or fracture-assisted diffusion seems to be the dominant mechanism of Pb-loss. Cooling curves, calculated using recently-measured Pb diffusion parameters, conform to the age-size relationship, and imply very slow cooling rates (1–2°C/myr or less), as might be expected for a terrane in which granulite conditions were maintained for an extended period of time. Our results, therefore, suggest a note of caution for interpretation of concordant zircon ages in meta-igneous rocks affected by high-grade metamorphism of long duration.
We report UPb and ages for multigrain fractions, single grains, and grain domains in zircons from highgrade igneous and sedimentary rocks of the Vavuniya Charnockite Province (VCP) in northern Sri Lanka, using the ionmicroprobe SHRIMP, a new vapour digestion technique (VDT) and evaporation. Charnockitic, enderbitic and mangeritic gneisses are derived from I-type tonalitic, syenitic, granodioritic and granitic precursors for which the UPb systematics of zircons as determined by SHRIMP suggest crystallization ages between ∼ 1000 and ∼ 1100 Ma. Many translucent, round and multifacetted zircons in these rocks are not of metamorphic but of igneous origin and acquired their shape through partial zircon dissolution and recrystallization. The large majority of zircons exhibit severe and variable Pb-loss some 540–580 Ma ago which we ascribe to granulite-grade metamorphism, almost immediately followed by local retrogression. Most of the zircons lost Pb from the entire grain with no domains remaining that reflect the original Pb isotopic composition. It was therefore impossible to obtain meaningful evaporation ages for such grains, and this cautions against use of this method in zircons that experienced severe Pb-loss. However, zircons formed during high-grade metamorphism apparently retain their primary Pb isotopic composition and were dated successfully by the evaporation technique, yielding ages between 553 ± 26 and 560 ± 30 Ma. Conventional multigrain analysis and small fractions following VDT for two samples, although much more precise than the SHRIMP data, yielded only strongly discordant data points with patterns reflecting variable Pb-loss. These data alone would not have made it possible to obtain reliable primary zircon crystallization ages.
A UPb investigation of suites of zircons from five granulites in the Wami River area, Tanzania, yields a 17-points discordia with upper and lower intercepts at 714−49+36 Ma and 538−35+49 Ma, respectively. These systematics are interpreted to indicate an age of approximately 715 Ma (Pan African) for the M1 granulite-facies metamorphism, whereas the lower intercept is related to a stage in the uplift and cooling following the M2 amphibolite-facies retrogradation (elsewhere dated at approximately 650 Ma). Three of the granulites contain minor amounts of an inherited, > 1600 Ma old zircon component, probably derived from the igneous precursors of the granulites. A suite of zircons from the adjacent biotite gneisses may signal a provenance age of approximately 2600 Ma (Tanzania craton?), but the U-Pb systematics do not clearly reflect the amphibolitefacies metamorphism (correlated with the M2 partial retrogradation of the granulites) that transformed the sedimentary sequences into gneisses (any petrographic record of a possible older metamorphic influence being absent). Biotite/whole-rock pairs from the same samples yield Rb-Sr ages between about 470 and 485 Ma for the granulites and about 458 Ma for the gneiss. They are interpreted as ‘cooling ages’ and set an age between about 485 and 460 Ma to the final cooling of the crust through the closure temperature of biotite to Rb-Sr. The subsequent granulite-facies and amphibolite-facies events and their chronology are fitted in the continent—continent collision model for the evolution of the Mozambique belt advocated by the first author.
New high-precision U–Pb zircon ages for 14 granitoid rocks of the Seychelles, including samples from Mahé, Praslin, La Digue, Ste. Anne, Marianne, Fregate and Recifs Islands, yield dates between 748.4±1.2 Ma and 808.8±1.9 Ma, interpreted as representing magmatic crystallization ages. U–Pb zircon ages as young as 703 Ma have been reported by other workers, and the time span of Seychelles magmatic activity, therefore, is ∼100 Myr. The vast majority of ages, however, fall in the period 748–755 Ma, suggesting a major period of granite plutonism at this time. At least some Seychelles dolerite dikes have equivalent ages, indicating the contemporaneity of granitic and basaltic magmas, and supporting field and chemical evidence for the production of minor quartz dioritic rocks by hybridization and magma mingling. Possible correlatives of the late Neoproterozoic (∼700–800 Ma) granitoids and dolerites of the Seychelles include volcanic and plutonic rocks in Madagascar and northwestern India (Malani Igneous Suite, Rajasthan), which may have formed in a continuous continental (Andean-type) arc located at the western margin of the Rodinia supercontinent. This idea is more consistent with the time span of magmatism, petrologic character of the igneous rocks, and paleomagnetically determined reconstructions, than the commonly held view of an intra-plate extensional setting for the Seychelles and Malani Igneous Suite.
Extensive terranes of basement reactivation are interpreted as resulting from crustal thickening following continental collision. It is suggested that terranes, such as the Grenville Province and much of the Variscan orogenic belt in Europe, have their modern analog in the Tibetan Plateau. The Tibetan Plateau is underlain by a continental crust between 60 and 80 km thick and is characterized by extensive high-potash Neogene vulcanism. Following T. H. Green's arguments that partial melting of a dioritic lower crust may yield potassic granitic liquids and refractory anorthositic residues, we consider that continental collision is followed by crustal thickening, to accommodate further plate convergence, with ensuing partial melting of the lower crust. At high structural levels, silicic-potassic ignimbrites are extruded in intermontane basin-horst terranes, with subjacent granite plutons. At deeper levels, a dry refractory lower crust consisting of pyroxene granulites and anor-thosites is generated.
The Rodinia reconstruction of the Neoproterozoic Supercontinent has dominated discussion of the late Precambrian Earth for the past decade and originated from correlation of sedimentary successions between western North America and eastern Australia. Subsequent developments have sited other blocks according to a distribution of ~1100 Ma orogenic belts with break-up involving a putative breakout of Laurentia and rapid reassembly of continent crust to produce Gondwana by early Phanerozoic times. The Rodinia reconstruction poses several serious difficulties, including: (a) absence of palaeomagnetic correlation after ~730 Ma which requires early fragmentation of continental crust although geological evidence for this event is concentrated more than 150 Ma later near the Cambrian boundary, and (b) the familiar reconstruction of Gondwana is only achieved by exceptional continental motions largely unsupported by evidence for ocean consumption. Since the geological evidence used to derive Rodinia is non-unique, palaeomagnetic data must be used to evaluate its geometrical predictions. Data for the interval ~1150-500 Ma are used here to test the Rodinia model and compare it with an alternative model yielding a symmetrical crescent-shaped analogue of Pangaea (Palaeopangaea). Rodinia critically fails the test by requiring Antarctica to occupy the location of a quasi-integral Africa, whilst Australia and South America were much closer to their Gondwana configurations around Africa than implied by Rodinia. Palaeopangaea appears to satisfy palaeomagnetic constraints whilst surmounting geological difficulties posed by Rodinia. The relative motions needed to produce Gondwana are then relatively small, achieved largely by sinistral transpression, and consistent with features of Pan-African orogenesis; continental dispersal did not occur until the Neoproterozoic-Cambrian boundary. Analogies between Palaeopangaea and (Neo)pangaea imply that supercontinents are not chaotic agglomerations of continental crust but form by episodic coupling of upper and lower mantle convection leading to conformity with the geoid.
Jurassic and Cambro-Ordovician paleomagnetic pole positions deduced from rocks of Sri Lanka and Antarctica generally conform when Sri Lanka is juxtaposed with the coast of Lützow-Holm Bay, East Antarctica, in a manner similar to a current Gondwana reassembly. The Highland and Southwest groups (mostly Proterozoic) of Sri Lanka are correlated with the Ongul and Skallen groups of East Antarctica on the basis of similar lithology, structural characteristics, structural trend, tectonothermal history (ranging from early Proterozoic to Mesozoic), and the pressure-temperature-time path of the main metamorphism. Some neighboring lithotectonic units are also comparable between the two areas. Fracture-lineament systems of Sri Lanka and Antarctica formed after the latest Silurian and during or before the Jurassic conform in this reconstruction. An improved fit of the 2000 m isobaths of India-Sri Lanka-Antarctica and continuation of the latest Archaean mobile belt from Enderby Land to peninsular India is obtained by fitting Sri Lanka into Lützow-Holm Bay, and Enderby Land into the embayment in the east coast of peninsular India. This juxtaposition of peninsular India to East Antarctica involves about 80 km northward movement and about 30° clock-wise rotation of Sri Lanka relative to India. The reassembly thus obtained accords well with data, supporting the idea that East Gondwana existed from the earliest Proterozoic to middle Mesozoic, although some disruption-collision events of limited scale are considered possible.