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The Neoproterozoic Supercontinent: Rodinia or Palaeopangaea?
Abstract
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.
... In their introduction, they state: 'Piper postulated that palaeomagnetic data from all the continents could be fitted to a common apparent polar wander path (APWP). This led him to suggest that a supercontinent composed of most of the continental crust remained in a quasi-rigid configuration throughout the bulk of Precambrian time (Piper, 1976(Piper, , 2000. Palaeomagnetic poles published in the late 1970s and early 1980s generally had poor age control and allowed sufficient flexibility to fit almost any pole on the rather tortuous APWP proposed by Piper (see review in Van der Voo and Meert, 1991).' ...
... Although 24 years, during which the database has multiplied, should either have refined or refuted a model proposed a quarter of a century ago (cf. Piper, 1976Piper, , 2000, Meert and Torsvik have used variants of this statement in all their papers on Proterozoic palaeomagnetism to dismiss the need to test the Palaeopangaea interpretation although, as I show here, this quasirigid model actually accommodates the palaeomag-netic data and the geological evidence much better than their own assessment. ...
... A large data set from the Sveconorwegian Belt is also conspicuous by its absence (Stearn and Piper, 1984) although Meert and Torsvik have included poles from metamorphic rocks, overprints, some poles with only approximate age indicators, and a pole from India with a quality factor of only one. Many of these excluded poles have been shown to be compatible with the Palaeopangaea reconstruction but in conflict with the Rodinia assumption (Piper, 2000). However, to make it clear that I am not selecting data to prove Palaeopangaea, I adhere rigidly to their data selection here (Table 1). ...
... Long-term, Paleo-to Neoproterozoic or even Archean connection between Precambrian terranes of Siberia and Laurentia in the structure of the Columbia/Nuna supercontinent (Rogers and Santosh, 2002;Zhao et al., 2002) have been proposed on the basis of geological, geochronological and palaeomagnetic constraint (e.g., Price, 1978, 2003;Piper, 2000;Hoffman, 1991;Condie and Rosen, 1994;Frost et al., 1988;Rainbird et al., 1998;Didenko et al., 2015;Ernst et al., 2016;Priyatkina et al., 2020). For example, Sears and Price (1978) and Piper (2000) attach eastern margin of Siberia to the western margin of Laurentia, while connection of the Palaeoproterozoic Taltson-Thelon orogenic belt of Laurentia and different provinces of the Siberia was proposed by (Hoffman, 1991; the Anabar Shield), (Condie and Rosen, 1994; the north-east end of the Akitkan belt), (Rainbird et al., 1998; the south-west end of the Akitkan belt), and (Frost et al., 1988; the West Aldan and Uchur terranes). ...
... Long-term, Paleo-to Neoproterozoic or even Archean connection between Precambrian terranes of Siberia and Laurentia in the structure of the Columbia/Nuna supercontinent (Rogers and Santosh, 2002;Zhao et al., 2002) have been proposed on the basis of geological, geochronological and palaeomagnetic constraint (e.g., Price, 1978, 2003;Piper, 2000;Hoffman, 1991;Condie and Rosen, 1994;Frost et al., 1988;Rainbird et al., 1998;Didenko et al., 2015;Ernst et al., 2016;Priyatkina et al., 2020). For example, Sears and Price (1978) and Piper (2000) attach eastern margin of Siberia to the western margin of Laurentia, while connection of the Palaeoproterozoic Taltson-Thelon orogenic belt of Laurentia and different provinces of the Siberia was proposed by (Hoffman, 1991; the Anabar Shield), (Condie and Rosen, 1994; the north-east end of the Akitkan belt), (Rainbird et al., 1998; the south-west end of the Akitkan belt), and (Frost et al., 1988; the West Aldan and Uchur terranes). Ernst et al. (2016) and recently Priyatkina et al. (2020) correlated the Angara Belt, Magan terrane and eastern part of the Siberian Craton with Wopmay and Taltson-Thelon belts, and the eastern part of the Rae Craton of the Laurentia, respectively. ...
... Neoarchean Hartmann et al. (1979Hartmann et al. ( , 2000aHartmann et al. ( , 2000b, Sato et al. (2009), Basei (1985, Basei et al. (1998b, 2000, 2009), Siga Jr et al. (1995, Harara (2001 Cingolani et al. (2002), Rapela et al. (2007), Santos et al. (2003a), Peel and Preciozzi (2006). Table 3. ...
... There is a general consensus that a supercontinent formed between ~ 1,200-1,000 Ma, although its exact configuration remains speculative (Paleopangea: Piper 2000, Rodinia: McMenamin and McMenamin 1990, Hoffman 1999, Li et al. 2008). Subsequently, this supercontinent brokeup into several fragments creating a series of basins during the Neoproterozoic time (ca. ...
The reconstruction of ancient continental margins encompassed in continent–continent collision is a complex task. The continental blocks generally record a multiphase evolution with interaction of tectonic settings, plate polarities, basins and their depositional architecture.
The Ribeira belt (Southeast-Southern Brazil) resulted from the juxtaposition of several crustal blocks during the Brasiliano/Pan-African tectonic events (800–490 Ma) leading to the amalgamation of Western Gondwana. In this context, a series of pre-Brasiliano blocks underwent variable rates of tectonic reworking, including fragments derived from Rodinia.
Some of the metasedimentary strata of the Southern Ribeira belt are representative of Late Meso- to Neoproterozoic basins which bordered these pre-Brasiliano continental fragments, such as the Capiru Group.
The Capiru Group (Late Meso- to Neoproterozoic) is a low-grade metasedimentary unit that crops out on the Curitiba microplate and records passive to active continental margin stages.
In this work we show new provenance data (U-Pb geochronology of detrital zircon) of the Capiru Group and compare them to the other chrono-correlative continental margin units of the region (Lajeado and lower Itaiacoca groups).
Through the evolution of Capiru, Lajeado, and Itaiacoca groups we show that the post-Rodinia continental margins of the Southern Ribeira belt show similar Paleoproterozoic contributions (2,000 – 2,185 Ma) and slightly different Mesoproterozoic populations, suggesting distinct paleogeographic contexts: the Capiru Group was deposited on the Northern margin of the Curitiba-Angola block, with Mesoproterozoic “exotic” contribution (1,508 – 1,100 Ma). On the other hand, the Lajeado and Itaiacoca groups were deposited on the East-Southeastern margin of the Paranapanema continental block.
... Несмотря на то что среднепротерозойский (ранне и среднерифейский) этап развития земной коры остается недостаточно освещенным, имеется версия, что существовавший в это время супер континент Палеопангея (по [Piper, 2000]) или Колумбия (по [Rogers, Santosh, 2002;Zhao et al., 2004]) начал распадаться в среднем рифее (рис. 4.22). ...
... Согласно палеомагнитным реконструкциям [Piper, 2000], в период с 1240 по 1000 млн л. н. отколовшаяся континентальная плита Балтика дрейфовала к югу от палеоэкватора, разворачиваясь при этом по часовой стрелке примерно на 160° так, что ее присоединение к позднерифейскому суперконтиненту Родинии в конце этого периода произошло уже другой стороной, т. е. со стороны Скандинавской окраины (см. рис. ...
В коллективной монографии на основе анализа и обобщения всей совокупности имеющейся геолого-геофизической информации, накопленной за прошедшие 50 лет, даются современные представления о глубинном строении земной коры Белого моря и прилегающих территорий. Объектом исследования является бассейн Белого моря, находящийся на сочленении северо-восточного склона Фенноскандинавского щита и Русской плиты. Акватория моря и прилегающая суша носит название Беломорский регион или Беломорье. Считается, что структура сформировавшихся здесь в архее докембрийских блоков континентальной коры региона сохранилась до настоящего времени. Подтверждением того является совпадение источников крупных аномалий гравитационного и магнитного полей Фенноскандинавского щита и различие в форме и положениях аномалий северо-западной части Мезенской синеклизы. Последний факт свидетельствует о процессах протерозойского рифтогенеза и последующей тектоно-магматической активизации на северо-восточном краю Восточно-Европейской платформы. Внимание авторов сосредоточено на результатах инструментальных сейсмологических наблюдений, полученных в последние годы, явлениях и процессах, порождающих сейсмичность, и других проявлениях современной геодинамики. Обобщение и комплексная интерпретация накопленных данных по геологии, тектонике, геофизике позволили выявить новые детали глубинного строения литосферы, уточнить ее состав, возможную геологическую природу и геодинамические условия ее формирования.
This joint monograph presents the modern concept of the deep crustal structure of the White Sea and adjacent areas based on analysis and assessment of available geological and geophysical information obtained over the past fifty years. The goal of the project was to study the White Sea basin located at the contact of the northeastern slope of the Fennoscandian Shield and the Russian Plate. The White Sea basin and the adjacent land are collectively called the White Sea Region. It is believed that the structure of the Precambrian blocks of the region’s continental crust formed here in Archean time has preserved up to the present day. This assumption is supported by the coincidence of the sources of big gravity and anomaly field anomalies in the Fennoscandian Shield and by differences in the shape and position of anomalies in the northwestern Mezen syneclise. This evidence is indicative of Proterozoic rift formation followed by tectonomagmatic activation on the northeastern margin of the East European Platform. The authors focused their attention on the results of instrumental seismological monitoring obtained in the past few years, as well as phenomena and processes which provoke seismicity
and other modern geodynamic processes. Analysis and interpretation of available geological, tectonic and geophysical data have increased our knowledge of the deep structure, composition and possible geological origin of the lithosphere and the geodynamic setting in which it formed.
... Ils constitueront les noyaux de plus grands cratons qui s'édifieront par la suite autour d'eux lors des futures phases de la tectonique des plaques, fonctionnant par accolements successifs d'aires continentales appelées 'terranes' (Fig. 2 ci-dessous, également Howell, 1995). Piper (2001) incluant les trois plus vieux assemblages continentaux (Arctica : 2,5 Ga ; Atlantica : 2,0 Ga ; Ur : 3,0 Ga). Nb: le terme 'Paléopangée' est utilisé par Piper (2001) pour rappeler la forme courbée N-S de l'assemblage des continents constituant la Pangée permo-triasique sensu stricto (voir Fig. 6). ...
... Piper (2001) incluant les trois plus vieux assemblages continentaux (Arctica : 2,5 Ga ; Atlantica : 2,0 Ga ; Ur : 3,0 Ga). Nb: le terme 'Paléopangée' est utilisé par Piper (2001) pour rappeler la forme courbée N-S de l'assemblage des continents constituant la Pangée permo-triasique sensu stricto (voir Fig. 6). En réalité le supercontinent illustré a pour nom Rodinia (voir ici et Fig. 4). ...
Cet article traite de l’évolution géologique de la plaque Antarctica, et fait suite aux trois récents articles publiés dans SCE par le Prof. Maurin sur la cryosphère actuelle (1/3, 2/3, 3/3).
1/ Les glaces fascinent …
Les glaces fascinent depuis longtemps les climatologues qui y voient un monde à part, aujourd’hui elles sont suivies ‘à la loupe’ car elles témoigneraient en tout ou en partie du processus de réchauffement actuel. Elles sont l’objet d’une attention médiatique constante. Pourtant elles furent souvent absentes de la Planète, elles apparurent plusieurs fois et disparurent autant de fois au cours de l’histoire géologique, le plus souvent suivant des modalités différentes à l’échelle temporelle et spatiale.
Il n’est pas possible ici de retracer la longue histoire des glaces qui commence au Précambrien, au moins à la transition Archéen et Protérozoïque (avec la glaciation huronienne, il y a environ 2,4 Ga, pour l’échelle détaillée des temps géologiques voir ici, et ci-dessous (Fig. 1) pour une version simplifiée) et se poursuit avec des aléas divers avec un recouvrement des glaces sur l’ensemble de la Planète à la fin du Néoprotérozoïque, donc y compris dans la zone équatoriale, donnant lieu au fameux ‘Snowball Earth’ ou hypothèse de la Terre boule de neige ou encore ‘Terre gelée’ (glaciation marinoenne qui a fait suite à la -ou les ? glaciation(s) sturtienne(s)- il y a 635 Ma. Ensuite viendra la glaciation Gaskiers vers 580 Ma, c’est-à-dire vers la fin du Précambrien. Cet épisode marinoen d’englacement généralisé perdura plus d’une dizaine de millions d’années avec des calottes de glace sur l’équateur (ici) et est à l’origine du nom de l’avant-dernière période du Précambrien, à savoir le Cryogénien (partie supérieure du Protérozoïque entre 850 Ma et 635 Ma, cf. Fig. 1). Entre ces deux grandes glaciations précambriennes (celles de l’huronien et du marinoen), soit sur un peu plus de 1,5 Ga aucune autre glaciation n’a encore? été rapportée, ce qui supposerait que pendant cet intervalle de temps le climat s’est maintenu dans des conditions plutôt chaudes, avec une régulation thermique ‘sans faille’ (Ramstein, 2015). Notons également pour être complet la présence de glaciers locaux à 2,9 Ga dans l’Archéen d’Afrique du Sud (glaciation ‘pongolienne’) (ici).
... The position of the Yangtze Block (YZB) within the South China Craton (SCC) is still controversial in the reconstruction of the Rodinia supercontinent (e.g. Li et al. 1995Li et al. , 2002aPiper 2000;Jiang et al. 2003;Meert & Torsvik 2003;Wang & Zhou 2012). Previous studies have regarded the SCC as a missing link between the Australia and Laurentia cratons based on stratigraphic correlations, tectonic analyses and palaeomagnetic studies (e.g. ...
... Previous studies have regarded the SCC as a missing link between the Australia and Laurentia cratons based on stratigraphic correlations, tectonic analyses and palaeomagnetic studies (e.g. Li et al. 1995Li et al. , 2002bPiper 2000). The position of the YZB has also been assigned to a location external to the Rodinia supercontinent by considering the latest results, including detrital zircon age patterns and palaeomagnetic and stratigraphic data (e.g. ...
The evolutionary history of the NW Yangtze Block is important in interpreting its location and relationship with the Rodinia supercontinent. Although a Neoproterozoic arc-related tectonothermal event is recognized in the Micangshan area of the NW Yangtze Block, its timing and P–T conditions are poorly constrained. We address this issue by focusing on the garnet–biotite gneiss that represents the main lithology of the Huodiya Group on the NW margin of the Yangtze Block. This gneiss is predominantly composed of garnet, biotite, feldspar and quartz. The peak mineral assemblage in the matrix consists of garnet + biotite + quartz + plagioclase + K-feldspar. The retrograde stage is characterized by embayed rims of the garnet and its associated biotite in the matrix. The P–T conditions in the peak and retrograde stages are constrained to 7–8 kbar and c. 710°C and 5–6 kbar and 650–675°C, respectively, and suggest that 4–5 vol.% melt was produced during an upper amphibolite–granulite facies metamorphic event. The first report of monazite U–Pb dating in the Huodiya Group of the Micangshan area yielded a weighted mean ²⁰⁶ Pb/ ²³⁸ U age of 802 ± 5 Ma. The studied samples contained detrital igneous zircons with ²⁰⁶ Pb/ ²³⁸ U dates >800 Ma, whereas the metamorphic zircons yielded a weighted mean ²⁰⁶ Pb/ ²³⁸ U age of 797 ± 9 Ma. Based on the compressional tectonic environment and previous studies, we propose that the Yangtze Block was probably located on the periphery of the Rodinia supercontinent.
Supplementary material: The analytical methods are summarized in Supplementary Text File 1. Representative mineral composition and the results of U–Pb isotopic analyses of monazites and zircons are presented in supplementary table 1–7 . The results of trace element concentrations in garnets are presented in Supplementary table 8 . https://doi.org/10.6084/m9.figshare.c.4698356
... Recognition that "Wilson-cycles" (Wilson, 1966) might reflect the assembly and dispersal of large landmasses led others to suggest the existence of earlier supercontinents in the 1970s Moores, 1970, 1972;Burke and Dewey, 1973;Irving et al., 1974;Piper, 1976;Sawkins, 1976). Piper (1976) was the first to propose a specific reconstruction of the Proterozoic supercontinent that he called "Paleopangea" (see also Piper, 2000Piper, , 2007. Other suggested names (sans reconstruction) were "Pangea-I" or "proto-Pangea" (Sawkins, 1976;Valentine and Moores, 1972;Bond et al., 1984). ...
... This 'strange attraction' between Laurentia, Siberia and Baltica was noted by Meert (2014). Piper (2000) also maintained Paleoproterozoic-Mesoproterozoic relationships between Laurentia, Baltica and Siberia in his Paleopangea configuration which differs from Columbia in that Siberia is positioned against the present-day western margin of Laurentia in a similar fit to the one proposed by Sears and Price (1978). Fig. 8b shows available poles for Laurentia from 1740 Ma to 1237 Ma (Q N 3 with radiometric ages; Table 1). ...
... Then, the study area was continuous subsidence, with a maximal extent in the Jurassic period. In the last stage, the study area was uplifted in the Yanshan and Himalayan movement ( Figure 2) (Hartnady, 1986;Tong, 1992;Piper, 2000;Wei et al., 2015). In the Gaoshiti area, as a result of the Tongwan movement, the fourth Member of the Dengying Formation experienced erosion caused by karstification (Hao et al., 2017). ...
Neoproterozoic marine microbialites have been targets for exploration and hydrocarbon reservoir development. The original depositional fabric and diagenesis control the pore systems of microbialites, leading to the complicated origin of microbialite reservoirs. This study aimed to reveal the origin of microbialite reservoirs following multi-stage diagenetic fluid activity in the fourth Member of the Dengying Formation in the central Sichuan Basin in southwestern China. The fourth Member of the Sinian Dengying Formation developed dolomitized microbialites, mainly including stromatolites, laminates, and thrombolites. Based on the background of tectonic movement, petrology and geochemistry examinations were executed to analyze the origin of the microbialite reservoir. Based on the cathodoluminescence and the homogenization temperature of the brine inclusions, it is credible that there were four stages of diagenetic fluid activities in the burial diagenesis. In the first stage, the microbialite reservoir was charged by oil in the Silurian period, with evidence from residual asphalt around the pores. In the second stage, dolomite precipitated to incompletely fill the pore spaces. In the third stage, the silica-rich diagenetic fluid with high temperature resulted in the precipitation of authigenic quartz. In the last stage, the oil charged again during the Triassic period, followed by siliceous filling, with residual asphalt filling the pore spaces. There were two stages of subaerial emergence, which occurred in two episodes of the Sinian-Early Cambrian Tongwan movement. The evidence for the two tectonic events includes two phases of dolomites with meteoric water origin, two cycles of V, Sr, and Na element profiles, two instances of negative excursion δ ¹⁸O isotope, and two cavity layers. By comparison, the karstification of reservoirs in the Tongwan III episode could generate a higher quality of reservoir than that in the Tongwan II episode. As a result, the quality of the microbialite reservoir from the fourth Member of the Dengying Formation was mainly improved by the subaerial exposure in the Tongwan III episode and then was partly destroyed by the siliceous filling. The identification of multi-staged diagenetic fluid charging can illustrate the evolution of the reservoir quality of Neoproterozoic microbialites.
... However, there are still debates, especially on the coeval tectonic setting, including three competing models of plume-rift, slab-arc, and plate-rift [1][2][3][4][5]. The position of the South China Block in Rodinia reconstruction also remains unclear [2,[6][7][8][9]. Scholars have proposed that the South China Block was originally placed in the interior of Rodinia [1,2,6] or adjacent to India and East Antarctica during the breakup of Rodinia to the Gondwana assembly in the Neoproterozoic [9][10][11]. ...
The Yangtze Block records Neoproterozoic magmatism and sedimentation related to the breakup of Rodinia and is an important piece in the reconstruction of the supercontinent. However, the tectonic setting and position of this block in Rodinia remain a subject of debate. In the present study, we report the zircon U-Pb ages and Hf isotopic composition of zircon and geochemical and Nd-Pb isotopic compositions for meta-volcanic rocks exposed in the Zhangbaling uplift of the NE Yangtze Block. The volcanic rocks, dominated by rhyolite and dacite, belong to the calc-alkaline series and show geochemical characteristics of arc rocks. Zircon U-Pb isotopic ages show that volcanic rocks in the Xileng Formation formed at ca. 790 Ma and ca. 760–700 Ma peaking at ~740 Ma. The late-stage volcanism was widely exposed in the uplift, characterized by a temporal-spatial trend becoming younger southwards. The old volcanic rocks have low initial εNd (−11.0) and εHf (−19.7 to −8.2) values and low Pb isotopic ratios, likely indicating an origin from ancient basement rocks underneath the Yangtze Block. The younger ones, being similar to continental arc andesite in trace element compositions, have relatively high initial εNd (mostly −4.6 to 0.5) and εHf (−0.4 to 8.8) values and high Pb isotopic ratios. These isotopic features point to an origin from the partial melting of juvenile crustal rocks. Sedimentary rocks of the Xileng Formation and the overlying strata also contain numerous zircon grains of ~700 Ma to ~630 Ma. The volcanic rocks in the Zhangbaling uplift might demonstrate long-lasting subduction along the northeastern margin of the Yangtze Block, probably active until ca. 700 Ma.
... Other geological characters that indicate geographic proximity between Archaean and Proterozoic cratons include matching 'piercing points' across tectonic features such as rifts (Bleeker and Ernst, 2006), linking of igneous clasts in sediments to source rocks on the basis of petrology, isotope analysis or other factors (e.g. Goodge et al., 2008), comparison of zircon age profiles (e.g., Smyth et al., 2007), involvement in collision orogenies (e.g., Piper, 2000), and matching of fossils, although this is of only limited use in the latest Neoproterozoic. For later reconstructions, fossil evidence is an important source of data (e.g., Dowding and Ebach, 2016). ...
... The Palaeoproterozoic supercontinent Columbia (between 2.5 and 1.5 Ga with maximum packing around 1.9 to 1.7 Ga) (Nance et al., 2014;Santosh and Kusky, 2010;Hou et al., 2008;Rogers and Santosh, 2002;Zhao et al., 2002;2004) and Neoproterozoic Rodinia (between ~1.1-0.9 Ga with maximum packing around 1.1 Ga), (Burrett and Berry, 2002;Sears and Price, 2002;Piper, 2000;Dalziel, 2000;Karlstrom et al., 1999;Brookfield, 1993) is now well accepted. Significantly enough, our limited published geochronologic data indicate that the evolutionary history of the cratonic basins ofpeninsular India overlaps with the timing of assembly and dispersal of these two supercontinents. ...
The Proterozoic cratonic basins of peninsular India
preserve records of repeated opening and closing of rifts
along the zone of Neoarchean sutures and/or along the
weak zones. These sedimentary basins, ranging in age
from late Palaeoproterozoic through Neoproterozoic are
traditionally referred to as Purana basins in Indian
literature. The successions of each of the basins may be
represented by successive unconformity-bound
sequences, which represent several cycles of fluvial-
shallow marine to shelf-slope-basin sedimentation
punctuated by local hiatuses and/or volcanic upheavals.
The advance retreat of ancient seaways and their complex
are recorded in the sedimentary successions of Purana
Basins.
Papaghni-Chitravati; Kaladgi-Badami; Lower
Vindhyan record the oldest cycle of sedimentation. These
basins opened after 2.0 Ga and closed by 1.55 Ga. The
Chattisgarh and its satellite basins, namely Indravati;
Khariar; Ampani opened after the 1.6 Ga. and closed
shortly after the 1000 Ma. Albaka; Mallampalli;
Kurnool; Bhima preserve Neoproterozoic sedimentation
history. The upper Vindhyan basin likely opened after
1.4 Ga. and continued through the Neoproterozoic. The
sequence of events indicates a close relationship of craton
interior histories with plate tectonics and variations in
the heat flow regime underneath the continental crust.
Periods of formation of the cratonic basins are coincident
with the amalgamation or fragmentation of
supercontinents further indicates genetic linkage between
the two processes. Synchronous development of the
cratonic basins with closely comparable stratigraphy and
basin development events, in different small continents, strengthens the view that basin formation processes
operated on a global scale, and stratigraphic basin
analysis on a regional scale is a significant tool in
evaluating the basins’ history. The available
stratigraphic, geochronologic or palaeomagnetic data
from India is still inadequate, and further information is
required to constrain its definite position in the context
of global tectonics.
... The Palaeoproterozoic supercontinent Columbia (between 2.5 and 1.5 Ga with maximum packing around 1.9 to 1.7 Ga) (Nance et al., 2014;Santosh and Kusky, 2010;Hou et al., 2008;Rogers and Santosh, 2002;Zhao et al., 2002;2004) and Neoproterozoic Rodinia (between ~1.1-0.9 Ga with maximum packing around 1.1 Ga), (Burrett and Berry, 2002;Sears and Price, 2002;Piper, 2000;Dalziel, 2000;Karlstrom et al., 1999;Brookfield, 1993) is now well accepted. Significantly enough, our limited published geochronologic data indicate that the evolutionary history of the cratonic basins ofpeninsular India overlaps with the timing of assembly and dispersal of these two supercontinents. ...
... 这些变化包括大陆重组、 海洋和大气化学组成、气候变化等 [21] . 新元古代与寒 武纪之交发生的重大地质事件(图 1)主要包括: 1) 在 中元古-新元古代之交, 全球大陆在低纬度集合形成 一个Rodinia联合大陆 [60,61] , 这一大陆自新元古代早 期开始分裂, 在Rodinia联合大陆解体以后, 大约在 6~5.2 亿年期间在南半球地体重组形成了一个影响整 个古生代的冈瓦纳大陆. 因此, 多细胞生物在新元古 代早期的出现、 后生动物的分异以及随后的寒武纪生 物大爆发等生物事件与当时地体的重组在时空上相 吻合 [62] ; 2) 联合大陆开始分裂一方面增加了大陆边 缘海的范围, 增强了大陆风化作用, 促进了生物的原 始生产率, 加大了全球范围内有机碳埋藏, 这一过程 导致大气CO 2 的急剧下降, 使得地球表面温度逐渐降 低导致冰盖的迅速扩展, 最后使地球陆地和海洋为 冰雪所覆盖, 从而导致雪球事件的发生 [61,63,64] . ...
... Proterozoic palaeogeographic reconstruction was carried out by the aid of limited palaeomagnetic data that suggested a single supercontinent throughout the Proterozoic (Piper et al., 1976) that was later called Palaeopangea (Piper, 1982(Piper, , 2000. Conversely, (McWilliams, 1981) proposed that the data were more consistent with two (Johnson and Woldehaimanot, 2003;Kröner and Stern, 2005 ...
The Kid Metamorphic Complex (KMC) lies within the southeastern part of Sinai Peninsula, Egypt. It is about 1500 m thick volcano-sedimentary succession. The Um Zariq (UZ) Formation forms the lower most stratigraphic unit in the KMC. The KMC is underplated and bounded from the west by granitic bodies.
The UZ Formation is made of metapelites and minor calc-silicate unit in the lowermost part of the formation. The common metamorphic mineral assemblage of the metapelites Garnet+corderite+andalusite+graphite+biotite+staurolite+chlorite.
The calc-silicate unit is made up of Calcite+hedenbergite+diopside+andradite+grossular+biotite+alkalifeldspars+ epidote. The metamorphic mineral assemblage indicates metamorphism under upper greenschist to lower amphibolite facies. Estimated temperature of metamorphism for the metapelites ranges from 537 to 630 oC. Higher temperatures (up to 692 oC) are estimated from the calc-silicate mineral assemblage.
The UZ Formation hosts massive, disseminated and secondary sulfide mineralizations. The massive sulfide mineralization hosted in the metapelites is dominated by galena, sphalerite, arsenopyrite, löllingite and several silver minerals. The sulfide mineralization hosted in the calc-silicate unit is Cu-Co dominated. The sulfide minerals expose deformational features, which suggest that the sulfide mineralization witnessed the peak metamorphic conditions. In addition, latter hydrothermal fluids led to mobilization and re-distribution of base and precious metals.
Geochemical data of various rocks revealed anomalously high concentrations of arsenic. Mineralogical and geochemical data suggest that the precursor of the metapelites was As-rich. Later hydrothermal fluids were proposed to be the source of the remaining base and precious metals. We suggest porphyry and porphyry related mineralization (Epithermal and Skarn) for UZ mineralization.
Arsenic is a renowned carcinogenic toxic metalloid that pollutes groundwater. It is chiefly a geogenic contaminant i.e. derived from rocks and minerals. Exposure to water with arsenic concentrations above 10 μg/L (10 ppb) leads to many deleterious health effects. Comparison of arsenic concentrations from UZ rocks to those of proved contaminated regions revealed that mining in UZ would lead to catastrophic consequences if environmental regulations were not applied strictly.
... However, it still remains debated regarding the Neoproterozoic paleogeographic position of the SCB relative to other continents in the Rodinia and Gondwana supercontinents. The Neoproterozoic SCB was placed between the Australia and Laurentia (Li et al., 1995;Piper, 2000;Li et al., 2002), or was linked with the India (Jiang et al., 2003;Yu et al., 2008) within the Rodinia supercontinent. Besides, Paleomagnetic data indicated that the SCB was placed against the northwestern Australia and remote the northeastern India during the latest Neoproterozoic and Early Paleozoic . ...
... The Rodinia supercontinent reconstruction of 750 M.a. by Piper (1976Piper ( , 2000 (Fig. 106) and by Dalzieial (1997) andWeill et al., 1998 (Fig. 107) show the position of India at that time. Similarly, reconstructions of Rodinia at the Late Neoproterozoic (~ 600 M.a.) by Bond et al., (1984) (Fig. 108) shows a slightly different position of India. ...
... Âñå ýòî ïîçâîëÿåò ïîëàãàòü, ÷òî ðàññìàòðèâàåìàÿ âèõðåâàÿ ñòðóêòóðà ÂÅÏ ÿâëÿåòñÿ íå ïðîñòî óíàñëåäîâàííîé îò äðåâíåãî ñòðóêòóðíîãî ïëàíà òåêòîíè÷åñêîé ôîðìîé, à ñâÿçàíà ñ ïðîÿâëåíèåì âðàùàòåëüíûõ äâèaeåíèé. Òåêòîíîïëèòíûå ðåêîíñòðóêöèè òàêaeå ïîêàçûâàþò, ÷òî â ðèôåå ÂÅÏ èñïûòûâàëà çíàêîïåðåìåííîå âðàùåíèå [2,3,19]. ...
The basement’s top tectonics of the East European platform (EEP) has been considered on the basis of the modern mapping data. The importance of the long-lived tectonic zones that form the vortex megastructure has been justified.
Their Riphean — early Vendian evolution was associated with activation of the Paleoproterozoic tectonic zones, which were transformed into paleorifts (aulacogens). The systems of the EEP aulacogens show the features of nonlinear structure and development: their evolution proceeded in the mode of transtension inside asymmetrically organized space between the active and passive paleocontinental margins; most of the paleorifts display wedge-shaped morphology, signs of asymmetric rifting and blocks rotation, a complex combination of elements of shear zones and gentle detachment zones tectonics, the vortex megastructure of the entire rifts system. Using an «iris diaphragm» model and the reconstructions with reversing plate rotation makes possible to explain the main patterns of the long-lived vortex structure of the EEP.
... Ma e 1500 Ma. Vários nomes têm sido atribuídos a esse supercontinente Paleoproterozóico, tais como, Nena, Nuna, Paleopangea, Columbia, entre outros (Gower et al., 1990, Hoffman, 1997, Piper, 2000, Rogers & Santosh, 2002 (Zhao et al., 2002(Zhao et al., , 2004(Zhao et al., , 2006Hou et al., 2008a,b;Kusky & Santosh, 2009;Rogers & Santosh, 2009;Johansson, 2009;Goldberg, 2010;Evans & Mitchell, 2011;Bispo-Santos et al., 2008. Alguns autores acreditam que o supercontinente Columbia teve o ápice da amalgamação em torno de 1900-1850 ...
... It is separated into the Northern Red Sea Belt (Arabo-Nubian Shield) and the Southern Mozambique Belt. The ANS lies along the eastern margin of Africa and is generally thought to represent a zone of continent-continent collision on the scale of the northern Alpine-Himalayan orogeny although others favored a largely ensialic origin (Burke et al. 1977;Dewey et al. 1989;Stern 1994;Piper 2000;Guiraud et al. 2005). ...
The study of the geology of southern Egypt, in-between the Red Sea and the Libyan borders, south of latitude 24°30′N reveals a succession of the Precambrian Arabo–Nubian Shield along the Red Sea coast overlain by Paleozoic–Mesozoic sediments. The Paleozoic section in the study area is well developed in three sub-basins, namely, Uweinat–Gilf, South Nile, and Etbai. Paleozoic sediments are well developed in the three sub-basins mostly sandstones of Cambrian overlain by glaciogene sediment conglomerates at base namely Gabgaba Formation and by the Naqus Sandstone at top. The tectonic events during the Early Paleozoic Caledonian Orogeny are marked by several unconformities and tectonic uplift and down faulting expressed in the many faults in the Uweinat–Gilf and South Nile sub-basins. The Carboniferous is well-developed sandstones in the three studied sub-basins. The glaciation at the Permian is reflected in sea-level fall, hence continental sediments are well developed in many parts of Egypt—a phase of the Hercynian Orogeny. Volcanics are very well common in the study areas ranging in age from 48 to 34 Ma at Uweinat and Gebel El-Asr. Vulcanicity continued during the Paleozoic and Mesozoic at the Triassic of Nasab El-Balgum and in the south Western Desert, the south Eastern Desert, and Etbai area. The highly seismic conditions in southern Egypt continued up to very recent times where tremors were noticed in the 80s and 90s of the last century pointing to very unstable area.
... The quantitative comparison with the coeval composite dataset of the Tethyan Himalaya and the Higher Himalaya also suggests a good relationship among each other (Table 3). However, the relation is much stronger in the younger (Ordovician) samples ( Figure 1a; Meert & Lieberman, 2008;Meert & Torsvik, 2003;Piper, 2000Piper, , 2007. (Cawood & Korsch, 2008). ...
This paper presents the first ever detrital zircon U–Pb–Hf isotopic study for the Late
Neoproterozoic–Early Palaeozoic stratigraphic succession exposed in the Hazara Basin, Western
Himalaya, North Pakistan. This time span represents the break‐up of the supercontinent Rodinia
and final assembly of Gondwana. The detrital record of the Late Neoproterozoic succession
indicates well‐mixed detritus shed from within the Indian Craton, especially the Central Indian
provenance (including the Delhi Fold Belt, Aravalli Orogen, and Bundlekhand Craton). The εHf(t)
values are mostly negative, and Hf TDMC ages are clustered at 2.0–2.4 Ga, which indicates the
derivation from an ancient reworked crustal source. In addition, the presence of a few positive
εHf(t) values in the Late Neoproterozoic sequence indicates addition of the juvenile crust that
corresponds to the period of the Rodinia break‐up. However, dissimilarities with detrital signatures
from the Australian continent may indicate break‐up of the Rodinia supercontinent and
detachment of Australia from India prior to ~754 Ma, which is the depositional age of the Hazara
Formation. In addition, the angular unconformity at the base of the Abbottabad Formation represents
the compressional tectonics that might be associated with the Pan‐African (Indo‐Antarctic
Craton collision with the East African Orogen during 800–700 Ma) orogeny. The presence of the
metamorphism and deformation in the rocks below the unconformity supports such an event
prior to deposition of the Early Palaeozoic Abbottabad Formation. Similarly, the appearance of
the Pan‐African detritus in the Early Palaeozoic Abbottabad Formation could be due to the closure
of the ocean basin between Eastern and Western Gondwana along the Mozambique Suture. This
provenance change may indicate the final assembly of supercontinent Gondwana.
... The exact nature and location of Rodinia and the former geographic position of modern-day continental cratons remains under debate. Piper (2000Piper ( , 2007Piper ( , 2009) has criticised the entire idea of Rodinia's existence, favouring instead a different supercontinent, Paleopangaea, which is hypothesised to have been a generally coherent landmass from 2700-600 Ma. In this view, Rodinian continental reconstructions are seen as unlikely based on the improbability of the proposed continental movements (among other reasons), as these reconstructions require the individual landmasses to be isolated and move independently until their assembly. ...
The Adelaide Rift Complex, a sedimentary basin in South Australia, has a long history
spanning over 300 million years from the Neoproterozoic to the Cambrian. Over 100
individual formations make up the basin fill, documenting its geologic evolution from
incipient rift to passive margin and recording a wide range of depositional environments.
The basin is significantly affected by syndepositional salt tectonics and later structural
deformation, creating a well-exposed natural laboratory in which to examine sedimentary
systems that are rarely exposed elsewhere. This publication briefly summarises the basin’s
geology (focusing on sedimentology), and provides a starting point for further research
through reviews of both recent and older literature. The deposits discussed here may serve
as analogues for similar depositional systems in the subsurface during petroleum
exploration and development; some relevant analogues are also discussed, focusing on
those that also have a component of salt-sediment interaction.
... In this scenario the continents could have remained partially attached until the Mesozoic. Such tight clustering of the continents throughout Earth's early history would perhaps be consistent with a model of supercontinent evolution proposed by Piper (1982Piper ( , 2001Piper ( , 2013. ...
In a recent article in this journal,
Paolo Sudiro (2014) considered the long history of the expanding Earth theory
and its recent descent into what he termed “pseudoscientific belief”. The
expanding Earth theory contends that the radius of the Earth was once
one-half to two-thirds of its current value, with the Earth's continents
forming a continuous sialic cover over the Earth. The theory has had two main
variants: slow expansion at about 0.5 mm yr−1 radial increase since
the time of Earth's formation and fast expansion at about 5 mm yr−1
since the Triassic. Focusing on Maxlow's model, Sudiro thoroughly addresses
the possibly insurmountable difficulties of the fast version, such as an
improbably high density and surface gravity prior to 200 Ma. He omits,
however, any discussion of the slow expansion model, which has a longer
history and far fewer theoretical difficulties. Moreover, recent evidence
from space geodesy, gravimetry and seismology indicates that the Earth at
present may be slowly expanding at 0.1–0.4 mm yr−1. It is concluded
that Sudiro's obituary of the expanding Earth theory as a whole must
be considered premature at this time.
... In the last three decades, the paleomagnetic database has been expanded and the quality of the data has improved. However, it is possible to conclude today that the supercontinent configuration developed by Piper (1976Piper ( , 2000 is not supported by paleomagnetic data currently available (Symons, 1991;Meert et al., 1994;Torsvik and Meert, 1995;Gala et al., 1998). Other authors such as Rogers (1996), Meert (2001), Rogers and Santosh (2002), Pesonen et al. (2003) and Zhao et al. (2003Zhao et al. ( , 2004, based mainly on the age of ancient mobile belts found in several cratonic blocks, suggest the existence of a Paleoproterozoic supercontinent. ...
The southwestern portion of the Amazonian craton, between the Ventuari-Tapajós province and the Andean chain, has been ascribed to a succession of orogenic events from 1.81 to 0.95 Ga, culminating with widespread anorogenic magmatism. Southwestward of the Serra do Cachimbo graben occurs the Juruena accretionary orogenic belt (ca. 1.81–1.51 Ga), previously included in the Rio Negro-Juruena and Rondonian/San Ignácio geocronological provinces or Rondônia-Juruena geologic province. The Juruena orogen proposed here includes the Jamari and Juruena tectonostratigraphic terranes, products of convergence which culminated in the soft collision of the Paraguá protocraton and the Tapajós-Parima arc system (Tapajós Province) ca. 1.69–1.63 Ga ago. Geophysical, geochemical, petrological and geochronological data and systematic geological mapping suggest that the convergent event resulted in a single orogenic system with two continental margin arcs, namely the Jamari and Juruena arcs. Modern geological and tectonic approaches, combined with aerogeophysics data, enable to interpreting this wide region of the Amazonian craton as a Paleoproterozoic orogen with well defined petrotectonic units and tectonoestructural framework. The Juruena orogen is an E-W trending belt, about 1100 km long and 350 km wide, inflecting to NW-SE, in Mato Grosso, Amazonas and Rondonia, Brazil. The general direction of the belt, its inflections and internal geometric and kinematic aspects of its macrostructures do not corroborate the general NW-SE trend of the originally proposed geocronological provinces.
... The White Sea rift system along the northeastern margin (in present-day bearings) of the EEC originated in transtensional regime with formation of pericratonic sedimentary basin at the passive margin of Baltica paleocontinent. According to paleogeodynamic reconstructions [73,76], the Baltica continental plate attached to Paleopangaea on the side of Timan margin started to break off from supercontinent approximately 1240-1265 Ma ago. Opening took place in the course of asymmetric rifting, i.e., by consecutive propagation of the rift away from the margin inland along with relative rotation of the continental plates to opposite sides: clockwise rotation of Laurentia and counter clockwise rotation of Baltica. ...
The region of the junction and interaction between the East European Craton (EEC) and the West Arctic Craton (WAC) is regarded as a complexly built zone or assembly of both the volumetric and dividing linear tectonic elements: the Trollfjord–Rybachi–Kanin (TRK) Lineament, the pericratonic subsidence zone of the EEC, the Karpinskii Lineament, the Murmansk Block of the Fennoscandian (Baltic) Shield, and the Kolmozero–Voronya Zone, which are briefly characterized in this paper. Evidences of thrusting have been established not only in the TRK Suture Zone and on the Rybachi Peninsula, which represent a fragment of the Timanides fold–thrust belt, but also to the southwest, in the Upper Riphean and Vendian terrigenous sequences making up the Sredni Peninsula and related to the pericratonic trough of the VEC. Two phases of fold–thrust deformations with elements of left-lateral strike-slip offset pertaining to the activity and evolution of the lineament suture dividing the Sredni and Rybachi peninsulas have been recorded. The variously oriented fault–fold systems within this fault zone are evidence for multistage deformation and can be explained by an at least twostage change in the kinematics that control displacement along the fault. The disintegrated granitic massifs of the Archean crystalline basement tectonically squeezed out in the upper crust as protrusions are localized within TRK Fault Zone. Plagiogranitic bodies, which underwent superposed fault-fold deformations of both kinematic stages, are an evidence of the vigorous tectonic event that predated folding and two-stage strike-slip displacement along the TRK Fault—by thrusting of Riphean sequences from north to south toward the Archean craton. The nappe–thrust regional structure was formed at this stage; elements of it have been recognized in the Sredni, Rybachi, and Kanin peninsulas. The main stages of tectonic evolution in the junction zone between the EEC and the WAP have been revealed and substantiated.
... These processes represent one phase of the Wilson cycle (Wilson, 1966;Dewey and Spall, 1975) where continents recurrently disintegrate and reassemble and oceanic crust and lithosphere form, subduct and recycle, a process that is likely to have been ongoing for around 3 Ga (Cawood, 2006;Shirey and Richardson, 2011). The present-day margins of the Central and North Atlantic are a manifestation of at least two complete Wilson cycles: The supercontinent of Rodinia was assembled at the end of the Mesoproterozoic Grenvillian orogeny (Piper, 2000;Thomas, 2006), which after break-up was divided by the newly forming Iapetus Ocean. The closure of the Iapetus Ocean leads to the Paleozoic Caledonian-Acadian orogeny in the North Atlantic evolution of the North Atlantic region is likely controlled by inherited orogenic structures formed during the Caledonian. ...
Rifts and passive margins often develop along old suture zones where colliding continents merged during earlier phases of the Wilson cycle. For example, the North Atlantic formed after continental break-up along sutures formed during the Caledonian and Variscan orogenies. Even though such tectonic inheritance is generally appreciated, causative physical mechanisms that affect the localization and evolution of rifts and passive margins are not well understood. We use thermo-mechanical modeling to assess the role of orogenic structures during rifting and continental breakup. Such inherited structures include: 1) Thickened crust, 2) eclogitized oceanic crust emplaced in the mantle lithosphere, and 3) mantle wedge of hydrated peridotite (serpentinite). Our models indicate that the presence of inherited structures not only defines the location of rifting upon extension, but also imposes a control on their structural and magmatic evolution. For example, rifts developing in thin initial crust can preserve large amounts of orogenic serpentinite. This facilitates rapid continental breakup, exhumation of hydrated mantle prior to the onset of magmatism. On the contrary, rifts in thicker crust develop more focused thinning in the mantle lithosphere rather than in the crust, and continental breakup is therefore preceded by magmatism. This implies that whether passive margins become magma-poor or magma-rich, respectively, is a function of pre-rift orogenic properties. The models show that structures of orogenic eclogite and hydrated mantle are partially preserved during rifting and are emplaced either at the base of the thinned crust or within the lithospheric mantle as dipping structures. The former provides an alternative interpretation of numerous observations of ‘lower crustal bodies’ which are often regarded as igneous bodies. The latter is consistent with dipping sub-Moho reflectors often observed in passive margins.
... The Natal Metamorphic Province (NMP) forms part of a Grenville-age ($1.1 Ma) metamorphic belt which flanks the southern and eastern margins of the Kalahari Craton and extends from Namaqualand in the west, to Natal in the east. Grenvillian-aged orogens are considered to have welded Proterozoic microcontinents into the Mesoproterozoic continent Rodinia (Hoffman, 1991;Piper, 2000). Prior to the breakup of Gondwana, the NMP extended through the Falkland Islands (Cape Meredith Complex), into western Dronning Maud Land (east Antarctica) and curved northwards through the Haag Block into Mozambique (Grantham et al., 1988;Jacobs et al., 1993Jacobs et al., , 1999 (Fig. 1). ...
This study provides constraints on the ages of deformation events and fabric development in deformed rocks of the Margate Terrane of the Natal Metamorphic Province. The Margate Terrane forms the southernmost of three terranes considered to represent multiple arc accretion onto the southern margin of the Kalahari Craton, and geochronological data indicate that the Margate Terrane has a long history of sporadic magmatism from ∼1180 to ∼1025 Ma. Two granite sheets of differing structural age, as revealed by deformational fabric and cross-cutting relationships, were sampled for U–Pb (SHRIMP) dating from coastal outcrop at Southbroom (30°54′43.61″S, 30°20′1.61″E). The older sheet contains fabrics related to both D1 and D2 events, whereas the younger shows evidence for syn-D2 emplacement and contains an S2 fabric. For both intrusive sheets, zircon core domains showing magmatic zoning yielded ages that are statistically identical at 1075 ± 6 Ma. This is interpreted to represent the intrusion age of the older sheet, and to sampling of a xenocrystic population in the cross-cutting sheet due to assimilation. Zircons from both sheets show metamorphic rim zones with a mean age of 1042 ± 10 Ma, which is attributed to rim growth during development of the S2 foliation, close to the intrusion age of the younger sheet. The 1075 ± 6 Ma age is comparable to the ages of other granitic units in the Margate Terrane that intruded between ∼1091 and 1070 Ma and implies that all of these predated the D1 deformation, which is considered to record the accretion of the terrane onto the Kalahari Craton. The D2 event is characterized by northward-verging folds with a pervasive southward-dipping axial planar fabric S2, which largely overprinted the S1 fabric. Previously, the pure-shear D2 deformation was considered to be older than the narrow sinistral shear zones occurring within the Mzumbe and Margate Terranes. However, dating of the D2 event at 1042 ± 10 Ma indicates that these deformations are coeval, and represent deformation partitioning during a transpressional event at ∼1050–1025 Ma that may have been related to collision with Laurentia during the amalgamation of Rodinia.
... A radical revision to its palaeogeography was proposed (Evans 2009). All the while, Piper (2000Piper ( , 2007 continued to espouse his alternative 'Palaeopangaea' model, largely unchanged since its original inception in the 1970s but beginning to incorporate modest mobility to accommodate discordant palaeomagnetic data (Piper 2010). Exclusion of Gondwanan cratons was partly based on a consistently high-palaeolatitude location of Congo-São Francisco during the interval 1080 -1010 Ma, in contrast to the low palaeolatitudes of cratons bordering Laurentia through the same period . ...
The supercontinent-cycle hypothesis attributes planetary-scale episodic tectonic events to an intrinsic self-organizing mode of mantle convection, governed by the buoyancy of continental lithosphere that resists subduction during closure of old ocean basins, and consequent reorganization of mantle convection cells leading to opening of new ocean basins. Characteristic timescales of the cycle are typically 500-700 myr. Proposed spatial patterns of cyclicity range from hemispheric (introversion) to antipodal (extroversion), to precisely between those end-members (orthoversion). Advances in our understanding can arise from theoretical or numerical modelling, primary data acquisition relevant to continental reconstructions, and spatiotemporal correlations between plate kinematics, geodynamic events and palaeoenvironmental history. The palaeogeographic record of supercontinental tectonics on Earth is still under development. The contributions in this special publication provide snap-shots in time of these investigations and indicate that Earth's palaeogeographic record incorporates elements of all three endmember spatial patterns.
... Australia, Antártida e India). La amalgamación del Gondwana habría requerido unos 400 Ma (entre 900 Ma y 500 Ma), finalizando en el Cámbrico superior-Ordovícico inferior (Grunow 1999;Powell et al. 2001 Grunow 1999;Piper 2000). ...
... Ga through the worldwide Grevillian orogenic events and probably rifted apart at ca. 750 Ma (e.g. Li et al., 1999Li et al., , 2008aLi, 1999;Piper, 2000;Zhou et al., 2002;Torsvik, 2003;Ernst et al., 2007;Maruyama et al., 2007). Reconstruction of the Rodinia supercontinent is a topic of international interest. ...
This paper presents the first detailed zircon U–Pb chronology, major and trace element, and Nd–Hf isotope
geochemistry of two Neoproterozoic plutons (Shanhou and Jiangshan) along the northwest side of the
Jiangshan–Shaoxing suture, Zhejiang province, South China. The Shanhou pluton consists of gabbros,
dioritic rocks and monzogranites. SHRIMP and LA-ICP-MS zircon U–Pb dating indicates that the gabbros
(∼846 Ma), dioritic rocks (∼845 Ma) and monzogranites (∼847 Ma) were emplaced simultaneously. The
Jiangshan pluton consists mainly of dioritic rocks that were also emplaced in the middle Neoproterozoic
with a SHRIMP zircon U–Pb age of ca. 842 Ma. The Shanhou gabbros are mainly high-K calc-alkaline, and
are enriched in LREE and LILE and depleted in HFSE with marked negative Ta–Nb anomalies. They have
positive εNd (T) (2.0–3.5) and εHf (T) (in-situ zircon) (3.3). The Shanhou and Jiangshan dioritic rocks as
well as the Shanhou granites are also high-K calc-alkaline, enriched in LREE and LILE and depleted in
HFSE with marked negative Ta–Nb anomalies. They also show positive εNd (T) (0.1–4.7) and εHf (T) (insitu zircon) (0.8–5.0). Detailed elemental and isotopic data suggest that both plutons were formed in a
continental arc setting with gabbros derived from partial melting of subduction-modified mantle wedge.
Such gabbroic magmas underwent fractionation crystallization of clinopyroxene + amphibole, forming
the less felsic dioritic rocks. Progressive fractionation crystallization of amphibole + plagioclase from the
evolved melts with a little crustal assimilation produced the more felsic dioritic rocks and granites. Our
new data suggest that final amalgamation between the Yangtze and Cathaysia blocks postdated 842 Ma.
... However, the 377 14 Age and Origin of the Chilka Anorthosites, Eastern Ghats, India distinctly older ages of the Napier Complex of Antarctica compared to those from the Eastern Ghats precludes its involvement in any orogenic episodes recognized in the Eastern Ghats (Rickers et al. 2001). It must be noted however, that the different Rodinia configurations in the literature do have some drawbacks mainly because of the lack of reliable paleomagnetic data for the different elements of Rodinia (Piper 2000). ...
Scapolite is an important mineral in the metamorphism of calc-silicates, marbles, amphibolites, and metagabbros in the Lufilian-Zambezi belt of Zambia. Both field and petrographic studies on granite gneisses, amphibolites, and metagabbros from the Munali hills area, in the southern part of the Lufilian-Zambezi belt indicated that scapolitization was due to metasomatism. The scapolite occurs as a pervasive replacement of plagioclase in the Munali hills granite gneiss, amphibolites, and metagabbros, and is associated with mineral assemblages that are indicative of amphibolite-facies metamorphism. Results of mineral analyses show that all the scapolites have calcian-marialite compositions, which range from 27 to 47 Me % and XCl contents of 0.37-0.50 a.p.f.u. The anorthite equivalent (31-46 EqAn %) of the scapolites overlaps with that of coexisting plagioclase (21-48 XAn %). The composition of scapolite is similar to that of the Copperbelt region of Zambia, where there is documented evidence of evaporite horizons. Moderate to high NaCl salinities, which range from 0.2-0.5 mol, and high contents of Cl in scapolite indicate that metamorphism in the belt was accompanied by metasomatic introduction of NaCl-rich fluids, which were derived from evaporite horizons that existed in the metasedimentary succession in the belt. This study shows that evaporites, from which NaCl-rich fluids were derived, were widespread in the Lufilian-Zambezi belt and played an important role in the metamorphic history of the belt.
After a description of the main geological units and the present-day geotectonic setting before Gondwana amalgamation, this chapter summarises the tectonic evolution of the Antarctic continent from its inclusion as part of the Gondwana supercontinent to the breakup of this landmass and the repositioning of Antarctica at southern polar latitudes since the Early Cretaceous. The geological evolution of the Antarctic continent is then described considering two main time periods: (1) c. 600–450 Ma, covering the processes which were active immediately before and during the amalgamation of Gondwana; and (2) c. 450–180 Ma, including all the major events that occurred after the final stage of Gondwana amalgamation to the time immediately before the Gondwana breakup phase. A subsequent section is devoted to the 180 Ma to recent time window during which present-day Antarctica and the other southern continents and surrounding oceanic basins formed as consequence of the fragmentation of Gondwana, and when tectonic processes led to the drift and dispersion of the various continental fragments. After a general overview of the most significant plate tectonic stages, and coeval magmatic products, the chapter reviews the main geological findings from the Ross Embayement region – one of the most investigated regions in Antarctica – the Transantarctic Mountains and the Ross Sea sector of the Western Antarctic Rift System. Persistent open problems, and potential research themes, are discussed in the Conclusions.
Оn the basis of the analysis of the results of modern domestic, foreign and author's research, the problems of tectonic inheritance in the course of supercontinental cyclicity are considered, examples of it in the form of repeated manifestations of Wilson cycles within a specific zones, paleomagnetic data on the similarity of reconstructions of supercontinents of different ages are given. The deep, predetermining causes of this inheritance, consisting in the existence of weakened zones of the lithospheric mantle, controlling the processes of formation and decay of supercontinents, are shown.
Research subject. The Riphean paleorift system of the White Sea, most of which is overlain by the waters of the White and Barents Seas and the platform cover of the East European Platform. This allowed numerous researchers to classify it as an aulacogen. The system was revealed by geophysical methods in the relief of the crystalline basement of the platform in the form of a frame of deep extended trenches of northwestern strike, subparallel to the edge of the East European platform.
Materials and methods . Personal observations of the authors within the Onega-Kandalakcha paleorift, Baikal rift zone; a detailed study of seismostratigraphic sections of these zones; extensive literature data on the structure of modern rift zones. A comparative analysis of the structure of the most studied and currently active Baikal and East African rift systems, as well as the Karoo rift system of the Late Paleozoic origin with the paleorift system of the White Sea.
Results. The following types of structural parageneses, which are characteristic of both modern rift systems and ancient paleorift systems, were identified. 1. Genetic relationship (inheritance?) of riftogenic structures with more ancient basement structures. 2. Structural paragenesis of concentric complexes in rift propagation zones. 3. Comparability of the area of horizontal extension of the lithosphere of the White Sea paleorift system with extension zones of modern continental rifts. 4. The fundamental similarity of the structure: the complex of paleorifts of the White Sea with modern continental rift systems: the presence of long deep trough segmentation of grabens and semi-grabens separated by bridges, which were accommodation zones with polarity reversal along the strike of the rift zone, displacement of the rift relative to the mantle ledge, the existence of a gently dipping normal fault (detachment), etc.
Conclusion . The riftogenic nature of the aulacogens in the northeastern segment of the East European Platform has been confirmed.
Research subject . Main problems of the General Stratigraphic Scale (GSS) of the Upper Precambrian including uncertainties in the hierarchy of subdivisions are analyzed.
Results. Prospects for detailing the Upper Precambrian GSS are discussed, along with questions of its correlation with International Chronostratigraphic Chart (ICSC) and establishing the lower boundaries of chronostratigraphic subdivisions. The importance of unifying the existing views is emphasized.
Conclusions. It is proposed to carry out the following reforms of GSS: to abolish Acrothemes / Acrons; to approve the Proterozoic (as well as the Archean) as an Eonotheme / Eon; to minimize the use of terms “Upper Proterozoic” and “Lower Proterozoic”; to assign the Riphean and Vendian to the rank of Erathem / Era (while preserving the status of the Vendian as a System / Period); to consider Burzyanian, Yurmatinian, Karatavian and Arshinian as Systems / Periods of the Riphean. Attention is focused on the Upper Riphean-Vendian interval. The lower boundary of the Upper Riphean (Karatavian) was proposed to establish according to the first appearance of the Trachyhystrichosphaera sp. microfossils. Then, the Terminal Riphean (Arshinian) lower boundary should be traced to the base of the tillites formed during the global Sturtian glaciation (which approximately corresponds to the base of the Cryogenian in ICSC). Apparently, the Vendian lower boundary may be raised to the level of the top of the Gaskiers tillites, as the deposits of the last major glaciation in the Precambrian. The indicated proposals are substantiated. It is necessary to form work groups to develop solutions.
En ce qui concerne plus directement le futur englacement, l’Antarctique, isolé tectoniquement à l’entrée du Cénozoïque avec l’ouverture de l’océan Antarctique Sud, subit les effets de l’orogenèse alpine traduisant un épisode important d’activité tectonique (plissement majeur). L’Antarctique étant en position polaire (depuis le Mésozoïque), la tectonique des plaques et la modification de la circulation océanique qui en résultent expliquent une part importante des phénomènes et le refroidissement du début du Cénozoïque, notamment enregistré par les isotopes de l’oxygène (18O/16O) des sédiments marins du Pacifique (in Van Vliet-Lanoë, 2013) et des tests de foraminifères. Aujourd’hui la plaque Antarctique est bordée de rides divergentes (en extension) et de zones de fractures qui fonctionnent depuis environ 100 Ma (Rogers & Santosh, 2004) suite à l’éclatement du Gondwana.
The paleoposition of North China Craton in Rodinia has long been in controversial. This paper mainly focuses on the U–Pb geochronological studies of detrital zircons obtained from Bayan Obo Group exposed in Shangdu Area, Inner Mongolia, aiming to provide more information for interprating this problem. Based on the acquired data, this paper comes to the following conclusions. Firstly, the depositional age of Bayan Obo Group might be from Meso– to Neoproterozoic according to the zircons U–Pb dating results. The lower succession of this group, namely Dulahala and Jianshan Formation deposited between 1800 and 1650Ma. The Halahuogete and Bilute Formation deposited between 1500 and 1350Ma. For Baiyinbaolage and Hujiertu Formation, their depositional age was 1250–900Ma. Secondly, for the provenance of Bayan Obo Group, this paper believes detrital zircons with age of 2.51–2.71Ga and 2.00–2.48Ga were from Guyang, Xi Ulanbulang and Zhuozi area; the Khondalite Belt provided detrital zircons with age of 1.95–1.80Ga; zircons with age of 1.60–1.75Ga might come from granitic rocks in Miyun Area. The magmatism after 1.60Ga was rarely recorded in the NCC, therefore those zircons with ages younger than 1.60Ga might come from outside of NCC. The magmatism with the same age existed in Baltic, Amazonia and Laurentia. Based on previous paleomagnetic researches, this paper proposes that NCC might receive detritus from Baltic during 1560‐1350Ma and had affinity with Laurentia and Amazonia at ∼0.9Ga in Rodinia. Baltic, Amazonia and Laurentia might be potential provenances for non–NCC detritus in Bayan Obo Group.
There are three stages in tectonic evolution of the Earth: (1) nucleation, from the origin of protocratons to their assembly into the Kenorland supercontinent (2.7–2.5 Ga); (2) cratonization, from the breakup of Kenorland (2.45 Ga) to the assembly of Columbia (1.85 Ga) and its reorganization into Rodinia (1.0–0.72 Ga); and (3) modern plate tectonics, from the breakup of Rodinia 720 Ma until the present. Analysis of the time-space reorganizations of Archean granulite–gneiss terranes, which correspond to continental lithospheric keels, reveals five groups of protocratons (Nena, Ur, Congo–Sahara, NAsia and Atlantica) that remained almost intact during long time intervals. After the breakup of Kenorland, the continental crust rotated counterclockwise. NAsia and Atlantica rotated the least and drifted relative to Nena; however, the latter rotated by 180○. Congo‒Sahara, Ur, and Kalahari rotated the most. The assembly and breakup of the supercontinents clearly correlates with secular changes in dominant types of base, precious, and ferrous metal deposits, as well as the formation and emplacement of diamonds.
Just over 15 years ago, a proposal forwarded by Rogers and Santosh (2002) posited the existence of a pre-Rodinia supercontinent which they called Columbia. The conjecture invigorated research into the Paleo-Mesoproterozoic interval that was; in our opinion, inappropriately dubbed ‘the boring billion’. Given the wealth of new information about the supercontinent, this review paper takes a careful look at the paleomagnetic evidence that is used to reconstruct Columbia. Our contribution represents a status report and indicates that; despite the exponential increase in available data, knowledge of the assembly, duration and breakup history of the supercontinent are contentious. The commonality of ~1.7-2.1 Ga orogenic systems around the globe are indicative of major changes in paleogeography and growth of larger landmasses. There is continued discussion about the interconnectedness of those orogenic systems in a global picture. Arguments for Columbia posit a ~1500-1400 Ma age for maximum packing. Paleomagnetic data from many of the constituent cratons during the 1500-1400 Ma interval can be interpreted to support a large landmass, but the consistency of the proposal cannot be reliably demonstrated for earlier or later times. One of the more intriguing advances are the apparent long-lived connections between Laurentia, Siberia and Baltica that may have formed the core of both Columbia and Rodinia.
A global tensional system of mid-ocean ridges was discovered at the end of the 1950s. All the world's oceans were proved to be young Mesozoic-Cenozoic structures and these new ideas in geotectonics led directly to the theories of ocean floor spreading and plate tectonics. The development of the idea of ocean floor spreading proved to be a crucial turning point in modern geotectonics. These facts could suggest the expansion of the Earth. However, the view that invoked Wegener's theory of continental drift - plate tectonics - which assumed a constant size for the Earth, remained the most prevalent idea. From this point of view, plate tectonics is just a hypothesis for a non-expanding Earth. The followers of plate tectonics believe that the drift of the continents relies on their movement upon the asthenosphere. New oceanic crust has to be consumed in the so-called subduction zones, compensating for the growth of the Earth. If the process of the opening of the oceans is a unidirectional global process - and it is not compensated for - then the Earth will increase in size. The process of the widening of new oceans, such as the Atlantic, Arctic and Indian oceans, should be simultaneous with the shrinking of the Palaeo-Pacific Ocean. If the Pacific Ocean expands, then the expansion of the Earth is inevitable. © 2017 The Author(s). Published by The Geological Society of London.
The climate system of the Earth is influenced by many terrestrial and astronomical factors. Nevertheless, fluctuations in the system are not chaotic but suggesting a limited number of governing factors. The relative significance of main climatic factors is estimated from comparison of expected consequences with real climatic events. The evolution of the atmosphere related to geotectonic development of the planet determined irreversible cooling of the Earth surface and formation of biota during the last three billion years. The trend of slow cooling was complicated by an intricate system of scale-variable quasiperiodic climatic oscillations. Superlong and long fluctuations with periods of hundreds and tens million years are best correlative with cycles of the Earth endogenic activity. Causes of medium-scale climatic fluctuations with periods of millions years are not so clear. As is shown in many works, short climatic fluctuations with periods of tens and hundreds thousand years were mainly caused by variations in parameters of the Earth orbit, the inclination of the Earth rotation axis included. Astronomical control over these fluctuations is also evident from their manifestation throughout the Phanerozoic history regardless the changing tectonic, paleogeographic, biotic, and general climatic environments on the Earth. Some short-period climatic fluctuations could be determined by sporadic methane influxes from destructed large gas-hydrate deposits. Most of the shortest climatic fluctuations with periods of millenniums or shorter are probably related to changes in solar radiation. The factors mentioned above were most influential among the others and actually controlled climatic fluctuations. Other processes only modified the climatic changes. The quasi-periodic, not chaotic (as it could be expected for a complex open system) mode of climate changes on the Earth can be explained precisely in terms of a limited number of governing factors.
The main palaeocontinents during the early Ordovician were Gondwana, Laurentia, Baltica, and Siberia, and a brief survey is made of their limits in the Ordovician and Silurian. In particular Gondwana. by far the largest continent, is analysed as including a core of South America. Antarctica, Africa, Australia and peninsular India, and also the marginal terranes. all of which show faunal links with. but which may not have been attached, to the core, of Avalonia, Ibero-Armorica and other European fragments, Turkey, Arabia, and terranes from the Far East including South China, Sibumasu and parts of Australasia. Changes within the benthic faunas reveal that Baltica, whilst isolated in the early Ordovician, became united with Avalonia by the end Ordovician and the two with Laurentia by the mid-Silurian to form the new supercontinent of Laurussia. Island arcs had distinctive faunas during the Ordovician, in particular those in the Iapetus between Laurentia. Baltica and Gondwana and the huge Kipchak Are which ran from Baltica to Siberia. As the period progressed, the Iapetus arcs became subducted beneath or accreted to their neighbouring cratons, and the Kipchak Are gradually collapsed to form the core of the new Kazakhstania terrane. Gondwana drifted over the South pole and this movement is reflected in the cratonic benthic faunas, particularly brachiopods and trilobites. which in the early Ordovician had formed a dine between the high-latitude faunas of North Africa and the equatorial faunas of the Far East and Australia, but by the Devonian lived in much warmer seas in southern Europe and cooler waters in Antarctica. The faunas also reflect the global palaeoclimates, which were warm in the early to mid Ordovician and mid to late Silurian but which were much colder in the half million year period of the late Ordovician and early Silurian, particularly in the latest Ordovician Hirnantian ice age with its attendant widespread Hirnantia brachiopod Fauna. The relative closeness of the chief palaeocontinents by the early Silurian enabled brachiopod and trilobite: larvae to cross the narrower oceans, enabling a relatively cosmopolitan benthic fauna to be established over much of the globe, apart from the cooler-water higher latitude Clarkeia Fauna to the south and the Tuvaella Fauna to the north.
Supercontinents are assemblies of all or nearly all (> 90%) of the earth's continental blocks. The oldest supercontinent speculated is the one at 3. 0 Ga termed as Ur. It is difficult to test the existence of this supercontinent due to its old age. There appear to have been twice in earth [email protected]
/* */ history when all of the continents were fused into one supercontinent. The first truly coherent supercontinent in earth history was probably Columbia, which formed between 1.85 and 1.90 Ga, began to fragment at ∼1.6 Ga, and finally broke up at ∼1.3-1.2 Ga. Columbia was followed by the second supercontinent Rodinia, which lasted from ∼1100 Ma to 540 Ma. The Pangea (0.25 Ga) was not a true supercontinent, but an unusually large assembly of continents making a semi-supercontinent. The southern half (Gondwanaland) of this semi-supercontinent has a dispersion history, and the northern half (Laurasia, i. e. Paleo-Asia) has an amalgamation history. At present, the third supercontinent has not formed yet, and our planet is in midway to make a true supercontinent (Amasia) in the future. The mechanisms of formation and disruption of supercontinents have been two controversial topics. A synthesis of some of the recent conceptual models suggests that mantle dynamics exerted a significant control on the assembly and breakup of supercontinents through the history of the Earth. The formation process of super-continents is controlled by super downwelling that develops through double-sided subduction zones as seen in present-day western Pacific, and also endorsed by both geologic history and P-wave whole mantle tomography. The super downwelling swallows all material like a black hole in the outer space, pulling together continents into a tight assembly. The fate of supercontinents is managed by superplumes (super-upwelling) which break apart the continental assemblies. With the advancement in numerical modeling techniques as well as the enhancement in computational power and resource, the numerical studies of mantle dynamics have markedly progressed toward the realization of seismic tomography images of mantle structure and a better understanding of geodynamic mechanisms. The solid Earth can be considered to comprise a plate tectonics domain with broadly horizontal motion in the upper mantle, plume tectonics dominated by vertical movements in the lower mantle region and an "anti-plate tectonics" zone characterized by horizontal movements at the bottom of the mantle. Although mantle tomography opens windows into the deep Earth, the imbricated remnants of "ocean plate stratigraphy" preserved in accretionary orogens still constitute useful geological tools to study subduction-accretion-collision history, particularly in relation to the assembly of older supercontinents on the surface of the globe. The dynamics of supercontinents also impact the origin and extinction of life, surface environmental changes as well as magmatism and metallogeny. Massive flow of material and energy was induced by mantle downwelling and upwelling accompanied by supercontinent assembly and breakup, which would also lead to large-scale magmatism and metallogeny, catastrophic environmental changes, sometimes even triggering mass extinction. When a rising mantle plume impinges the base of a supercontinent, the consequent continental rifting, formation of large igneous provinces, large scale metallogeny and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to carry out the resource assessment, to understand the history of life, and to trace the major surface environmental changes of our planet.
The studied sector comprises high grade metamorphic rocks formed during the Neoproterozoic - Ordovician evolution of central Ribeira Fold Belt (SE Brazil). The new ID-TIMS U-Pb geochronological results for a charnockite and a diatexite of the studied area suggest that metamorphic peak conditions occurred at ~570 Ma. These results further support the idea that both extensive production of granitoid melts (diatexites) and charnockite/granulite formation in the area was simultaneous and that the recently suggested genetic relation between these rock types is consistent.
New paleomagnetic data have been obtained from the Neoproterozoic subvolcanic intrusions which are widespread in the Biryusa terrane of the southwestern margin of the Siberian craton. The mafic dike swarms called the Nersa complex are rift-related subvolcanics, which could be used as indicators of the initial stage of the Neoproterozoic breakup of the Rodinia supercontinent. Two stable components of magnetization from the Nersa intrusions and Neoproterozoic sedimentary rocks of the Karagas series have been obtained. One of them is possibly a synfolding component related to the Early Paleozoic deformation processes. The other is the characteristic component of remanent magnetization, with the site-mean direction characterized by D s = 146.4, Is, = 11.0, and α95 = 13.3. The nature of this component is disputable. On the one hand, it can locate Siberia in the Late Neoproterozoic, but on the other hand, it can also reflect the Early Paleozoic remagnetization processes. Detailed analysis of the data, including results of reversal, baked-contact, and fold tests, suggests that the paleomagnetic directions could be of primary origin. We have tested the new paleomagnetic pole for its correspondence to some alternative tectonic reconstructions of Rodinia and believe that Siberia had an equatorial position and its modern southern margin was oriented to Laurentia during Neoproterozoic time.
Massif anorthosites are important Proterozoic continental crustal components with worldwide occurrences along linear belts. Two major questions concerning these massif-anorthosites are whether they have broadly similar ages, and whether their parent magmas are mantle-derived or lower continental crust-derived. The Chilka massif anorthosites, hosted by the Proterozoic Eastern Ghats mobile belt of eastern India, yield 855 ± 31 Ma U–Pb zircon crystallization age that overlaps with the breakup of Rodinia. This age is considerably younger than Grenville-age global massif anorthosites. Trace elements and Nd–Sr–Pb isotopic compositions of the Chilka anorthosites imply derivation from a depleted mantle source contaminated by late-Archean to early-Proterozoic lower continental crust. We suggest that this mantle upwelling to generate the Chilka anorthosites was a result of ‘edge-driven convection’ given that the Eastern Ghats Belt, hosting the Chilka anorthosites was located 1,000 km away from the margin of the southern Indian cratons in the Neoproterozoic Rodinia. Alternatively, we also consider that the anorthosites’ parent magma formed as a result of the regional extensional tectonism at ca. 850 Ma affecting this segment of Rodinia, as recently suggested by some workers.
The hypothesis that the Cordilleran geosyncline originated as an Atlantic-type continental margin by the rifting of an older Precambrian continental mass and the opening of a new ocean basin leads to the question of where the counterpart of the North American Precambrian craton may be. The Siberian platform-a large, discrete, older Precambrian craton, lodged in northeast Asia and surrounded by younger fold belts-is a likely candidate for the missing Precambrian continental fragment. The outline of its northeast margin fits the southwest margin of the North American Precambrian craton to produce a congruence of tectonic grain and age provinces. Both margins are overlapped by sediments of the same general type that began to accumulate about 1,500 m.y. ago, after the initiation of the separation.
A hypothesis for a late Precambrian fit of western North America with the Australia-Antarctic shield region permits the extension of many features through Antarctica and into other parts of Gondwana. Specifically, the Grenville orogen may extend around the coast of East Antarctica into India and Australia. The Wopmay orogen of northwest Canada may extend through eastern Australia into Antarctica and thence beneath the ice to connect with the Yavapai-Mazatzal orogens of the southwestern US. The ophiolitic belt of the latter may extend into East Antarctica. Counterparts of the Precambrian-Paleozoic sedimentary rocks along the US Cordilleran miogeocline may be present in the Transantarctic Mountains. Orogenic belt boundaries provide useful piercing points for Precambrian continental reconstructions. The model implies that Gondwana and Laurentia rifted away from each other on one margin and collided some 300 m.y. later on their opposite margins to from the Appalachians.
The Vendian/Cambrian segment of the Lauretian apparent polar wander path (APWP) has been poorly constrained and the subject of some controversy. The Catoctin volcanic province in central Virginia is well-dated at 570±35 Ma (Rb-Sr) and 597±18 Ma (U-Pb) and therefore presented an excellent paleomagnetic target for resolving the Laurentian Vendian-Cambrian APWP. A total of 206 samples from 32 sites were collected from the Catoctin basalts, feeder dikes and sills. The study revealed three ancient directions of magnetization. The results of this study and a reevaluation of previous paleomagnetic studies from coeval rock units leads to the proposal of a new APWP. This new APW track indicates that Laurentia was located near the pole during the interval 615-580 Ma and drifted rapidly (16cm yr-1) towards its Late Cambrian equatorial position. -from Authors
A new fit for Siberia and Laurentia in the Late Proterozoic places Siberia north of the Franklin orogenic front in the Canadian Arctic such that the Akitkan fold belt in Siberia aligns with the Thelon magmatic zone in Canada. Zircon ages from both belts range from 2.0 to 1.9 Ga and appear to record additions of juvenile crust. The match between the Archean Slave province in Canada and the Aldan province in Siberia also supports this fit. Common plutonic zircon ages in both provinces are >3.5 to 3.2 Ga, 3.1-2.9 Ga, and 2.8-2.6 Ga. The ˜1 Ga Grenville orogen may have extended northward between southern Greenland and Scandinavia, passing through east-central Greenland and adjacent Barentsia, and possibly into the Angara fold belt in Siberia. It is possible that three Early Proterozoic fold belts associated with the Aldan province are extensions of the Coronation Supergroup, an Early Proterozoic rift- to passive-margin succession deposited on the western margin of the Slave province.
The formation of the supercontinent Gondwana heralded the beginning of the Phanerozoic following a complex series of collisional events after the break-up of earlier supercontinental assemblages. Paleomagnetic data are used to help distinguish between these events and it appears that there are three critical periods of mountain building during Gondwana assembly. The first major orogenic event took place between 800 and 650 Ma and has been termed the East Africa Orogeny. This tectonic episode formed the Mozambique Belt and likely resulted from the collision of India, Madagascar and Sri Lanka with East Africa. The second and third orogenic periods during Gondwana assembly partially overlap in time. The Brasiliano orogeny (600–530 Ma) resulted in the amalgamation of the South American nuclei and Africa. The Kuunga Orogeny was proposed, in part, because of the recent collection of geochronologic data indicating a 550 Ma granulite forming event in East Gondwana and the observation that the apparent polar wander path for Gondwana does not form a spatially and temporally coherent pattern until roughly the same time. The Kuunga orogeny may have resulted from the collision between Australia and Antarctica with the rest of Gondwana.
Analysis of Vendian to Cambrian paleomagnetic data shows anomalously fast rotations and latitudinal drift for all of the major
continents. These motions are consistent with an Early to Middle Cambrian inertial interchange true polar wander event, during
which Earth's lithosphere and mantle rotated about 90 degrees in response to an unstable distribution of the planet's moment
of inertia. The proposed event produces a longitudinally constrained Cambrian paleogeography and accounts for rapid rates
of continental motion during that time.
Sea level changes during the Neozoic have been estimated by two different methods. The first involves measuring the amount of present-day land area which was flooded during the past, and using the present-day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding. The second involves the estimation of the changing volume of mid-oceanic ridges through time, and estimating sea level changes after having allowed for isostatic adjustment. A difference in sea level of 170 m is obtained from the two methods for the Cretaceous (80–100 m.y. B.P.). This is equivalent to a difference in continental flooding of 24 Mm2, using the present-day hypsographic curve.We attempt to explain this difference firstly by allowing for the fact that the present-day ocean basins have more sediment in them than did the Cretaceous ocean basins. This produces a sea level change in the opposite direction to that produced by the reduction in mid-ocean ridge volume since the Cretaceous. Secondly, we suggest another large factor in producing the difference is that the present-day hypsographic curve is not the correct one to use when studying sea level stands in the Cretaceous. Present-day average continental heights are closely related to continental areas. Accepting this principle, if continents are joined together in the past, their average height must be greater, and so their hypsographic curve must be steeper. A given sea level rise would produce less continental flooding during times of continental aggregation than it would today.
A possible palaeogeographic link between the Grenville and Rondonia-Sunsas provinces is reinforced by the timing of thermometamorphic and plutonic events. Equivalent terms of regional geological time scales are: Ketilidian = Transamazonian; Palaeohelikian or Elsonian = Rondonian-San Ygnacio; Neohelikian or Grenvillian = Sunsas; Hadrynian = Brasiliano. Remobilization of the older crust is another feature common to both provinces in Helikian times. Felsic volcanics extruded 1650 million years ago in the eastern Grenville Province show 1.6 Ga analogues in the Roosevelt lava flows of the Amazon Craton. Also a recently defined 1470–1500 Ma Pinwarian event in the Grenville shows correlatives in the final stages of evolution of the Rio Negro-Juruena belt.
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.
Precambrian palaeomagnetic data from Gondwana are reviewed with the goal of assessing the duration and magnitude of major intercratonic movements which may have occurred within the supercontinent during its evolution. The data suggest that Gondwana existed only from latest Precambrian or early Palaeozoic times up until its breakup in the Mesozoic. Prior to latest Precambrian times at least two major fragments are identifiable, East Gondwana (Australia, India, Antarctica) and West Gondwana (Africa, South America); these probably collided along the Pan-African Mozambique belt.
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
Middle-to-Late Proterozoic stratigraphy and metallogeny in the eastern part of the Canadian Cordillera and in South Australia are strikingly similar. In both areas, thick, predominantly shallow-water strata and their contained mineral deposits can be divided into three sequences (A, B, C) that record eposodic and prolonged continental rifting. It is proposed that Adelaidean strata of Australia were deposited adjacent to Belt-Purcell, Mackenzie Mountains and Windermere strata of the Canadian Cordillera within an epicontinental trough of a "Hudsonia' megacontinent. With the final rifting of this trough, the paleo-Pacific ocean was born. By Early Cambrian time, Australia-Antarctica was on the trailing "east' side of the nascent megacontinent, Gondwana, and was being modified on the "west' by accretion in the Pan-African event. North America, more or less surrounded by trailing edges at this time, was analogous to the Cenozoic African plate. This hypothesis accommodates the available paleomagnetic and radiometric data. It has implications for pre-Pangean plate tectonics, paleogeography, and the predictive metallogeny of both areas. -Authors
Remarkably similar deposits representing two Neoproterozoic glaciations
are present on the west and east sides of Laurentia. Although now
located near the margins of Laurentia, these glaciogenic successions
were formed within supercontinents. The older glaciogenic succession
(Rapitan-Sturtian, ˜700 Ma) is preserved in a series of pull-apart
basins formed when the supercontinent Kanatia fragmented to produce the
proto Pacific ocean. The younger Varangerian glaciogenic rocks
(˜600 Ma) are now scattered throughout the North Atlantic region,
but formed in basins that reflect the demise of a second Neoproterozoic
supercontinent (Rodinia) and heralded the formation of the Iapetus
ocean.
A pre- to syn-rift sequence (upper Little Dal Group, Coates Lake Group) in the Mackenzie Mountains of northwestern Canada reveals paleomagnetic directions in pigmental hematite (THB, RRB) that are similar to hematite overprint directions (P2) of underlying Late Proterozoic strata. Paleopoles of these magnetic components from the Thundercloud and overlying Redstone River formations of the Coates Lake Group are respectively 202°W, 27°N (N=6 sites, A95=9°) and 206°W, 32°N (N=4 sites, A95=10°)The primary paleopole for the basal Thundercloud Formation (THA) at 210°W, 01°N (N=6 sites, A95=21°) is close to a previously reported pole (222°W, 2°N) from diabases (dated by U-Pb at 778 ± 2 Ma) that intrude strata below Little Dal Group. The large error in THAI caused by scatter along a small circle, is here attributed mainly to tectonic rotation of azimuths of section-mean directions. Based on this interpretation, the THA pole position suggests a minimal unconformity below the Thundercloud Formation, contemporaneity of the sills and the basalts that cap the Little Dal Group, and uncomformity between Thundercloud and Redstone River Formations. Anomalous directions from the Little Dal basalts, and sequential directions in magnetic phases of the Redstone River Formation are also interpreted to record local block rotations during trans-tensional tectonism.The P2 disseminated pigmental hematite magnetization is interpreted to immediately postdate magnetizations from most other hematite phases, as well as magnetizations from (reduced) sulphide/magnetite beds at the base of the Coppercap Formation (upper Coates Lake Group). P2 is absent from, and likely predates deposition of, the upper Coppercap and overlying formations.Some poles (P3) that postdate P2 poles and indicate high paleonatitudes are here interpreted as Late Precambrian. Negative fold tests suggest that most other high-latitude poles from Late Proterozoic units of the region are of Cretaceous Laramide age.
PALEONTOLOGYIn this issue of Science (p. [879][1]) and in this week's Nature , two groups report finding microscopic fossils of animals and embryos exquisitely preserved in 570-million-year-old phosphorite rocks in south-central China. These new fossils offer a first glimpse of familiar-looking animals before the Cambrian explosion 540 million years ago, and show how a full record of the dawn of animals might be assembled. By showing that phosphate can fossilize tiny, fragile organisms from such ancient times, the finds have opened up a new way of looking for an older record of animals, say paleontologists.
[1]: http://www.sciencemag.org/cgi/content/short/279/5352/879
Global gravity data and seismic inferences of lateral inhomogeneities in the density distribution of the Earth's mantle provide information on convection in the lower mantle. The data are interpreted in terms of a model of mantle convection with two layers separated by the interface corresponding to the 670 km seismic discontinuity. It is shown that the observations are in approximate agreement with theoretical deductions for a l=2 convection mode in the lower mantle.
The case for a single supercontinent in Proterozoic times is examined in the context of a modified reconstruction with the Precambrian shields collectively comprising a primary lens-shaped body of crust. The palaeomagnetic data base is now sufficient to provide a definitive test of this model and it is shown that palaeopoles from the major shields conform to a single narrow path from ca. 2600 to 570 Ma. The agreement is especially compelling because the model requires no stringent data selection although it is itself highly rigid with adjustments only necessary at 1100 Ma and then applicable only to peripheral shields. There is close correspondence of the predominant field polarities from the constituent shields giving added confidence that the same polarities are being correlated, and the model supports the view that the global palaeoradius has been approximately constant since 2600 Ma. The pre-2200 Ma palaeopoles from Laurentia define ``track 6'' which is shown to be precisely applicable to the contemporaneous record from the African, the Australian, and possibly the Indian, Shields. The post-2200 Ma palaeopoles record higher rates of apparent polar wander (a.p.w.) movement although the magnitude of these movements is identified within one shield (the Laurentian) alone, and the data from other shields continue to conform to the unique reconstruction. The a.p.w. path is best constrained by the data from anorogenic igneous units over the intervals 2600-1800 and 1500-1000 Ma with second rank data from sedimentary successions in all of the major shields supporting the path defined by the igneous data. The a.p.w. paths over the intervals 1800-1500 and 1000-850 Ma are represented predominantly by uplift magnetisations in metamorphic terrains of the Fennoscandian and Laurentian Shields, although they are matched by magnetisations in supracrustal successions in Africa, South America and Australia, and in Africa and Siberia, respectively. The weakest part of the analysis covers the interval 800-570 Ma and the solution cannot yet be regarded as unique because it relies on magnetisations from sedimentary rocks; on the model developed here these data conform to a single a.p.w. path which specifically subdivides at the base of the Cambrian as the supercontinent was dismembered. Many Precambrian tectonic lineaments are brought into parallelism on this model and confirm the validity of the palaeomagnetic reconstruction. They include the later greenstones (2900-2200 Ma) formed in a permobile environment, and the straight belts and mobile belts formed in a coherent ensialic environment; there appears to have been a long continuity in the prevailing stress system in the crust linked to evolving small-scale to large-scale aesthenosphere systems. This analysis confirms that the continental crust has been a highly coherent unit since the beginning of Proterozoic times and restricts the tectonic models applicable to these times. The possibility of multi-continent plate tectonics is no longer an issue: it is not possible that the shields could have been repeatedly separated and returned to the same unique configuration necessary to satisfy the single a.p.w. path. Models of lithosphere evolution require that the continental crust stabilised towards the end of the Archaean retained a much higher relative strength than the oceanic lithosphere until late Proterozoic times.
Late Cambrian sandstones and limestones sampled from various members of the Riley and Wilberns formations of the Llano uplift show a progression of paleomagnetic pole positions as a function of age. The members, ages, and poles are the following for the Riley Formation: the Hickory Sandstone, Lower Dresbachian, 34°N, 145°E the Cap Mountain Limestone, Dresbachian, 33°N, 140°E the Lion Mountain Limestone, Upper Dresbachian, 24°N, 146°E. For the Wilberns Formation they are the following: the Welge Sandstone/Morgan Creek Limestone, Lower and Middle Franconian, 24°N, 151°E and the Point peak Shale, Upper Franconian, 6°N, 159°E. These poles are based on thermal, chemical, and alternating field demagnetizations and on vector analysis. Most directions are interpreted to be of reversed polarity, but the Cap Mountain Limestone also yielded normal polarity directions; all directions resided in hematite with blocking temperatures up to 680°C. Almost all Cambrian poles appear to fall in a broad streak between the equator at about 155°E (e.g., the poles from the Tapeats Sandstone and from the Late Cambrian Point Peak Shale of the Wilberns Formation) and about 60°N, 90°E, where Cambrian poles have been obtained by Elston and Bressler (1977) and French et al. (1977). Although, at the present time, partial to complete remagnetization or non-dipole behavior of the geomagnetic field are adequate ad hoc hypotheses to explain some of the data, it is suggested that the simplest and most unifying hypothesis to explain all data involves a Cambrian loop of apparent polar wander with respect to North America. This loop occurs before the middle Late Cambrian, with the poles from the Llano uplift falling on the return track.
We have made a regional paleomagnetic study of lithotectonic domains in the Central Gneiss Belt of the Grenville Province in Ontario along ten N-S and E-W traverses up to 200 km in length. Although originally intended to clarify the tectonic mechanism by which these exotic terranes were assembled and welded to the Archean Superior craton during the ~1150-Ma Grenvillian orogeny, we actually learned much more about the timing of post-orogenic uplift of the various domains around 1000-900 Ma as they stabilized and became part of the Rodinia supercontinent. The normal (N) and reverse (R) natural remanent magnetizations (NRMs) of all domains, as well as those of reactivated regions flanking the Grenville Front (GF, the Superior-Grenville boundary) to the north and south, have paleomagnetic poles falling on the 980-920-Ma ( 40 Ar/ 39 Ar calibrated) portion of the Grenville apparent polar wander track for Laurentia. There is a general tendency for paleopoles to young with increasing distance of domains from the GF, implying that more southerly domains were uplifted and magnetized later, but two of the domains do not fit this pattern. Previously reported younging trends away from the GF, based on K/Ar thermochron maps and paleomagnetic `zone poles', are untrustworthy because of hydrothermal alteration, which causes chemical remagnetization and anomalously old K/Ar ages near the GF. Another trend in our data is a regular increase in the R/N ratio with increasing distance south of the GF. In the reactivated zones flanking the GF, NRMs are overwhelmingly of N polarity, whereas well away from the GF, R/N is close to 50:50. Also, NRM intensities and susceptibility values increase 100-fold away from the GF, peaking 10 km south of the front, with a pulse-like pattern similar to that documented in anomalously high 40 Ar/ 39 Ar dates in the same region. Both the magnetic and Ar/Ar results are likely due to a `wave' of hydrothermal alteration and remagnetization during which fluids were driven away from the GF. Since the remagnetized NRM near the GF has approximately the same direction as NRMs in domains away from the GF, hydrothermal activity along fault systems south of the GF must have continued until ~1000 Ma, long after the collisional orogeny itself.
Using the most reliable palaeomagnetic data from the Siberian Platform we have constructed an apparent polar wander (APW) path extending between 1100 Ma and 250 Ma. From this we derive the palaeo-latitudinal drift history and orientation change of Siberia through the Neoproterozoic and Palaeozoic. Comparison of selected palaeomagnetic data from Siberia north and south of the Viljuy basin confirms a mid-Palaeozoic anticlockwise rotation of northern Siberia relative to southern Siberia. The rotation of approximately 20 degrees was first proposed by Gurevich in 1984. The Viljuy basin runs approximately east west along latitude 64°N. APW paths based on data compilations including, for example, Ordovician data from both the Lena river section (south) and Moyero river section (north) will be adversely affected by this relative rotation. The palaeomagnetic data indicate an inverted orientation for Siberia in `Rodinia times' (ca. 750 Ma) in a palaeo-latitudinal belt between 15°S and 20°N. This is inconsistent with a palaeo-position on the northern margin of Rodinia if the rest of Rodinia is located according to palaeomagnetic data from Laurentia, Baltica and East Gondwana. The final convergence between Siberia and Baltica is poorly constrained by palaeomagnetic data. At 360 Ma Siberia was in an inverted position in mid-northerly latitudes, separated from Baltica (to the south) by an east west oceanic tract approximately 1500 km wide. The next palaeomagnetic constraint on the position of Siberia is at 250 Ma which puts Siberia and Baltica together at the northern end of Pangea. The convergence of the two is characterised by the northerly drift of Baltica and clockwise rotation of Siberia. Although the APW paths for Siberia, Baltica and Laurentia differ, they imply broadly similar palaeo-latitudinal drift trends for the three continents. During the time-period studied all three continents start in southerly/equatorial palaeo-latitudes, drift south, then drift north, changing drift sense at approximately the same time. The smaller scale differences in palaeo-latitude change reflect the opening and closing of intervening oceans. The overall pattern of movements may reflect a large scale (temporal and spatial) geodynamic system which survived the construction and destruction of supercontinents. If we hold to the concept that true polar wander is not significant, we conclude that large continents, although intermittently separated by oceanic tracts, may be driven across the globe in a weak union for periods of 800 Ma or more.
New paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the Silurian and Devonian. In this paper, the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data. The data from the three fields of paleomagnetism, paleoclimatology, and biogeography are generally in excellent agreement, and an internally consistent paleogeographic evolutionary picture of the interactions between North America, Gondwana, and intervening displaced terranes is emerging. During the interval of the Ordovician, Silurian, and Devonian, North America stayed in equatorial paleoposition, while rotating counterclockwise. The northwest African part of Gondwana was in high southerly latitudes during the Late Ordovician and was fringed by peri-Gondwanide terranes, such as southern Europe (Armorica) and Avalonian basement blocks now found in eastern Newfoundland, Nova Scotia, the Boston Basin, the Appalachian Piedmont, and northern Florida. Subsequently, Gondwana and the peri-Gondwanide terranes displayed rapid drift with respect to the pole. This drift translates into the following pattern of movement for northwest Africa. During the latest Ordovician-Early Silurian, this area moved rapidly northward from polar to subtropical latitudes, followed by equally rapid southward motion from subtropical to intermediate (about 50°S) paleolatitudes during the Late Silurian-Middle Devonian. It is likely that significant east-to-west motion accompanied the latter shift in paleolatitudes, with the Caledonian-Acadian orogeny the result of Silurian to Early Devonian convergence and collision between Gondwana and North America. This collision sandwiched several of the intervening displaced terranes between Gondwana and North America. Subsequent to this collision, Gondwana was separated in the Late Devonian by a medium-width ocean from North America and the Avalonian and southern European blocks which were left behind adjacent to North America. This new ocean closed during the Carboniferous, and the resulting convergence and collision were the cause of the Hercynian-Alleghanian orogenic belt. Problems remaining for future research, besides the further gathering of reliable paleopoles, involve the uncertain pre-Devonian position of the southern British Isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid Late Ordovician-Silurian apparent polar wander for Gondwana.
Stratigraphic correlations and tectonic analysis suggest that the Yangtze block of South China could have been a continental fragment caught between the Australian craton and Laurentia during the late mesoproterozoic assembly of the supercontinent Rodinia. The Cathaysia block of southeast China may have been part of a 1.9 1.4 Ga continental strip adjoining western Laurentia before it became attached to the Yangtze block around 1 Ga. This configuration provides a western source region for the clastic wedges in the Belt Supergroup of western North America which contain detrital grains of 1.8 1.6 Ga and 1.22 1.07 Ga. The breakup of Rodinia around 0.7 Ga separated South China (Yangtze plus Cathaysia blocks) from the other continents.
Paleomagnetic data from East Gondwana (Australia, Antarctica, and India)
and Laurentia are interpreted to demonstrate that the two continents
were juxtaposed in the Rodinia supercontinent by 1050 Ma. They began to
separate after 725 Ma, allowing the formation of the Pacific Ocean. The
low-latitude Rapitan and Sturtian glaciations occurred during the
rifting that led to continental breakup. East Gondwana remained in low
latitudes for the rest of the Neoproterozoic, while Laurentia moved to
polar latitudes by 580 Ma. During the Vendian, a wide Pacific Ocean
separated the two continental land masses. The younger Marinoan, Ice
Brook, and Varangian glaciations in the early Vendian preceded a second
continental breakup in the late Vendian, causing formation of the
eastern margin of Laurentia and rejuvenation of its western margin.
Paleomagnetic data indicate that Gondwana was not fully assembled until
the end of the Neoproterozoic, possibly as late as Middle Cambrian.
Li and Powell (1998) are proponents of the popular Rodinia reconstruction which they use to challenge our revised assessment of the Neoproterozoic location of South China. We note the serious difficulties with the Rodinia configuration. These include (i) the requirement for a ~730 Ma break up although the geological evidence for this event puts the figure at ~550 Ma and (ii) the large scale, rapid and differential continental movements that are required to achieve the Gondwana reconstruction by late Neoproterozoic/early Phanerozoic times. The 850-550 Ma palaeomagnetic data are shown to accord with a conservative reconstruction which overcomes these problems and is analogous to Pangaea (Palaeopangaea). This reconstruction implies that the late Neoproterozoic transition to Gondwana was achieved mainly by sinistral transpression along the Pan African belts accompanying extinction of the Alfo-Arabian arc. A putative collision between blocks grouped as East and West Gondwana, which were supposedly widely separated in mid-Neoproterozoic times, is not required.
The Sveconorwegian belt is a broad terrain in the south western sector of the Fennoscandian Shield subjected to thermal activation, widespread intrusion and limited tectonic activity between ca. 1100 and 950 Ma, and magnetised during slow uplift and cooling following these mobile events. This study comprises a palaeomagnetic investigation of four areas spanning the zone: the anorthosite, farsundite and related intrusive complexes of southwest Norway, the gabbro-norite intrusions of the Bamble sector bordering the Oslo Graben, the gabbro-anorthosite complex at Brattön and Älgön in west Sweden, and dolerite intrusions near the eastern tectonic front to the zone in Sweden. Site mean directions and demagnetisation trends in the Rogaland intrusive complex define an apparent polar wander (a.p.w.) swathe of just over 30° of arc; poles fall along this swathe according to their position in the complex and their blocking temperatures, and the resultant path is interpreted as a migration of this zone away from the palaeopole at a rate of 1.3–3.0° Ma⁻¹. The total swathe represents 10–20° of a.p.w. movement at 900–940 Ma; an isolated later (‘Y’) magnetisation may represent a later extension of the path at ca. 840 Ma. Two sets of magnetisations, a NW negative, predominantly hematite-held, and SSW negative, predominantly magnetite-held, are recognised in the gabbro-norite intrusions of the Bamble sector and are linked to radiometric events at 1090 and 1010 Ma. In the Brattön and Älgön norite-anorthosite bodies of west Sweden, demagnetisation trends and site mean directions define a short swathe of westerly negative directions linked to radiometric ages averaging ∼ 1000 Ma. Minor dolerite (hyperite) bodies intruded near the eastern margin of the Sveconorwegian belt possess predominantly steep positive and negative directions of magnetisation comparable to results from the Scania region at the southern margin of the belt.
It is shown that the present geoid has a simple, low-order configuration with an axis of symmetry in the equatorial plane. It is shown further that it is a 'tennis-ball' pattern, with an equatorial high belt and a polar low one, which is clearly controlled by the rotation of the earth. Finally, it is shown that the outline of Pangea between at least 200 Ma and 125 Ma ago lay along a great circle passing through the paleopoles of rotation. Thus, it also had an axis of symmetry in the equatorial plane. This hemispheric supercontinent configuration ended in Middle Cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading, hotspot outbreaks and high sea-level stands. This evidence is interpreted in terms of separate steady state lower mantle convection, responsible for the present geoid, weakly coupled to the upper mantle one. This weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal. The complete cycle, from one supercontinent to the next, might be of the order of 400 Ma.
Rb-Sr mineral data are presented for the Sudbury and Mackenzie dolerites of Canada and for dolerites and lamprophyres from southwest Greenland. Five mineral isochrons or errorchrons, based chiefly upon feldspar separates, agree with twelve biotites from dolerites in defining best-fit ages between 1260 and 1190 m.y. Much older K-Ar and Rb-Sr mineral ages from country rocks demonstrate that the dolerite results are not due to regional heating, and basaltic magmatism in both regions between ∼1260 and 1190 m.y. is indicated (λ(87Rb) = 1.42 × 10−11 yr−1).This activity can be correlated with extensive dolerite sills in Sweden and Finland, the subject of parallel studies, which yield six mineral isochrons or errorchrons, ten Rb-Sr biotite ages from dolerites, and determinations by other methods falling between 1290 and 1155 m.y., although the Rb-Sr biotite ages are all grouped in the 1250-1210 m.y. range.Palaeomagnetic poles from the dolerites define tight clusters for each of Canada/Greenland and Fennoscandia. Superimposition of the two groups of poles leads to a non-unique reconstruction in which Fennoscandia may have adjoined Canada/Greenland at 1260-1190 m.y., but in an orientation quite different from that established for 1000-850 m.y. The necessary net rotation of Fennoscandia through 90° may have been achieved by splitting, separation and final reunion of the continents into a different relative disposition between ∼1190 and ∼1000 m.y. This favours the involvement of plate tectonic processes in the Grenville-Sveconorwegian orogeny. The 1260-1190 m.y. dolerites may represent the beginning of a continental separation which preceded the Grenville orogeny, although other causes for the magmatism cannot be ruled out.
Rb-Sr mineral ages and palaeomagnetic data are presented for nine dolerite dykes and sills in central and southern Sweden. The intrusions are representative of widespread dolerites, mainly dykes, which cut pre-Sveconorwegian (Svecofennian) crust and trend parallel to the Sveconorwegian Front Zone (or Schistosity Zone) over a band up to 150 km wide along most of its 700-km length. The Rb-Sr ages suggest emplacement through the approximate interval 1000-900 m.y. Cooling ages on country rocks show little evidence of significant Sveconorwegian (e.g. 1000 m.y.) heating effects, and the new isotopic and palaeomagnetic results are taken to represent the time of dolerite intrusion. The dolerites were emplaced in response to net tensional stresses in the Svecofennian crust: it is proposed that these were caused by marginal upwarping related to post-orogenic uplift of the adjacent Sveconorwegian region. The palaeomagnetic poles for the dolerites are similar to poles from the Sveconorwegian Province and the Front Zone, indicating that these also have a ca. 1000-900-m.y. age. The similar cooling histories of the Sveconorwegian Province and the Grenville Province of Canada allow this age to be assigned also to the Grenville poles. If so, it is not necessary to postulate plate motions during Grenville-Sveconorwegian magnetisation, and the agreement between dolerite poles and Sveconorwegian poles suggests that the orogenic belt cooled essentially in place against its bounding cratons. A possible continental fit shows Scandinavia and North America contiguous in late Grenville time, though relative motions before 1000 m.y. are not ruled out.
A palaeomagnetic study is reported of reddened facies (Fengtai Formation) of Neoproterozoic glacial rocks which underlie Early Cambrian rocks with disconformity in the Huabei (North China/Sino-Korean) Block. The diamictite (preferred age 620-600 Ma) carries a dual polarity remanence residing in hematite of the red matrix. The mean direction derived from 62 samples is DI = 205.9− 32.4° (α95 = 3.9°) yielding a pole position at 233°E, 62°N. Tests on the matrix deformed beneath dropstones suggest that remanence was fixed before full compaction, although clasts near the base of the formation are largely overprinted. Overlying Early Cambrian sediments of the Houjiashan and Yutaishan formations have a similar remanence also of dual polarity (DI = 205.5− 32.1°, α95 = 3.9°, 32 samples). The magnetisation in the diamictite is therefore interpreted to have been acquired during loading by the ice sheet and/or the overlying Cambrian succession. Red shales from the Liulaobei Formation (∼890-840 Ma) near the base of the Neoproterozoic succession in the Huabei Block yield a contrasting remanence of DI = 59.475.3° (α95 = 7.1°, 19 samples) equivalent to a pole position at 150°E, 43°N. Pole positions from this study accord with Lower-Middle Cambrian poles from the Australian and South China Blocks with North China sited adjacent to northeastern Australia in accordance with recent biogeographic and palaeogeographic models. Although the palaeolatitude derived from the Fengtai diamictite (17°) is Cambrian in age and probably later than the glaciation, the correlation with Australia implies that glaciation in North China took place in low palaeolatitudes (∼20°) and reinforces the view that late Neoproterozoic glaciation, at least at this perimeter of Gondwana, occurred at low latitudes. Neoproterozoic-Cambrian poles from North China, South China and Australia fail to conform to the popular Rodinia reconstruction with the latter blocks adjacent to western North America and also fail to support the view that Gondwana formed by the fusion of widely separated eastern and western segments during Pan African orogeny. Instead they accord to poles from Africa and South America in a precursor of Gondwana (Protogondwana). The subsequent Palaeozoic derivation of this supercontinent was probably achieved by intracontinental strike-slip motion during Pan African deformation following extinction of the Afro-Arabian arc.
Episodic growth of continental crust and supercontinents at 2.7, 1.9, and 1.2 Ga may be caused by superevents in the mantle as descending slabs pile up at the 660-km seismic discontinuity and then catastrophically sink into the lower mantle. Superevents, in turn, may comprise three or four events, each of 50–80 My duration, and each of which may reflect slab avalanches at different locations and times along the 660-km discontinuity. Superplume events in the late Paleozoic and Mid-Cretaceous may have been caused by minor slab avalanches as the 660-km discontinuity became more permeable to the passage of slabs with time. The total duration of a superevent cycle decreases with time reflecting the cooling of the mantle.
The end-Paleozoic Pangea appears to have contained three continents that had grown in the Precambrian and remained intact until Mesozoic rifting: Ur, formed at ∼3 Ga and accreted to most of East Antarctica in the middle Proterozoic to form East Gondwana; Arctica, an approximately 2.5-2 Ga continent that contained Archean terranes of the Canadian and Siberian shields and Greenland; and Atlantica, formed at ∼2 Ga of cratons of ∼2 Ga age that now occur in West Africa and eastern South America. Arctica grew at ∼1.5 Ga by accretion of most of East Antarctica plus Baltica to form the continent of Nena. Collision of Nena, Ur, and Atlantica, plus minor plates, formed the supercontinent of Rodina at ∼1 Ga. Rifting of Rodinia between 1 and 0.5 Ga formed three continents: East Gondwana; Atlantica (which became the nucleus for West Gondwana); and Laurasia (which contained North America, Greenland, Baltica, and Siberia). Gondwana formed at ∼0.5 Ga by amalgamation of its eastern and western parts. Various plates accreted to Laurasia during the Paleozoic, and collision of Gondwana with Laurasia created Pangea at ∼0.3 Ga.
The fundamental principles, techniques, and results of recent studies of paleomagnetism (PM) in the continental crust (CC) are presented in an introductory text. Topics addressed include the magnetic minerals; an outline theory of rock and mineral magnetism; field and laboratory PM methods; PM directions, poles, and apparent polar wander; Archean and Proterozoic PM; and CC growth and consolidation in Archean and Proterozoic times. Consideration is given to CC breakup and dispersal in the late Proterozoic and Cambrian; Paleozoic PM and the formation of Pangea; Mesozoic and Cenozoic PM and the breakup of Pangea; and the geomagnetic field, continental movements and configurations, and mantle convection since Archean times. Diagrams, drawings, graphs, and maps are provided.
Three major East Asian crustal blocks, the Tarim, North China and South China Blocks, have records of the Neoproterozoic rifting events that broke up the supercontinent Rodinia. A preliminary tectonostratigraphic analysis suggests that the Tarim Block may have been adjacent to the Kimberley region, the South China Block between eastern Australia and Laurentia, and the North China Block adjacent to the northwestern corner of Laurentia and Siberia during the early Neoproterozoic. All three blocks were probably separated from the larger cratons towards the end of the Neoproterozoic but stayed close to the Australian margins of Gondwanaland from Cambrian until Devonian.
The reconstruction of a Palaeoproterozoic continental block requires correlation between the major structural and lithological features of the main continental provinces. The African and American circum-South Atlantic continents, for example, can be brought together in a pre-ocean-opening fit and have therefore been the subject of many attempts at such correlation.The tectonic evolution of the Palaeoproterozoic fluvio-deltaic deposits in the West African, Guiana, Congo and São Francisco provinces is related to the 2-Ga collision orogeny. These formations either rest directly upon Archaean blocks, as is the case for the Francevillian in Gabon and the Jacobina Unit in Brazil, or they rest on the upper part of the Palaeoproterozoic, as with the Tarkwaian in Ghana and in French Guiana.They were deposited, in Guiana and Gabon, in tectonic settings of extension, in foreland and pull-apart basins. They are composed mainly of conglomerate and sandstone, and range from fluviatile, locally with debris flows, to deltaic. These sedimentary rocks were deposited after the initial stages of a collision orogeny dated at more than 2.1 Ga. This event was recorded, in Guiana and West Africa, by the inheritance of detrital zircons and pebbles of foliated metamorphic rocks in the basal conglomerates. In Gabon and Brazil, these detrital formations were deposited on Archaean continental margins that became involved in the orogeny only at a late stage. They are all interpreted as products of the collapse and breakup of the early orogenic mountain belt formed during the Palaeoproterozoic collision.The structural and metamorphic evolution of these deposits show many similarities throughout the provinces. The margins of the basins are overthrust by older Palaeoproterozoic or by Archaean rocks. Structural geometry and kinematics of deformation in shear zones and recumbent folds are consistent with the overall tectonic evolution of the Palaeoproterozoic provinces during the latest stages of the collision orogeny. Metamorphism was generally in the greenschist facies, but muscovite-andalusite parageneses are common and may be replaced by kyanite-chloritoid assemblages in relation with the thickening and burial during overthrusting of the older rocks. The P-T conditions (450°C and 3.5 kbar to 600°C and 5 kbar) indicate that some of the fluvio-deltaic rocks were buried to depths of more than 10 km. This implies significant underthrusting and the formation of mountain belts.Comparison of the tectonic evolution on either side of the South Atlantic shows that major convergence of the Archaean and Palaeoproterozoic terranes took place at ∼ 2 Ga, contributing to the establishment of new continental blocks. The tectonic style of the fluvio-deltaic formations indicates a frontal collision between the Congo and São Francisco provinces, whereas the collision between West Africa and Guiana was oblique, at least during the latest stages of the orogeny.
Laurentia, the rift-bounded Precambrian nucleus of North America, may have broken out from a Neoproterozoic supercontinent between East and West Gondwana. Several lines of evidence suggest that the Appalachian margin of Laurentia subsequently collided with the proto-Andean margin of the amalgamated Gondwana supercontinent in different relative positions during early and mid-Paleozoic time, in route to final docking against northwest Africa to complete the assembly of Pangea. Hence the Appalachian and Andean orogens may have originated as a single mountain system. The overall hypothesis retains the same paleomagnetic and paleobiogeographic controls as previous global reconstructions for the Paleozoic Era. Laurentia-Gondwana collisions may help to explain contemporaneous unconformities in the Paleozoic sedimentary cover of the Laurentian, Gondwanan, and Baltic cratons.
Paleomagnetic poles from the Upper Proterozoic Mackenzie Mountains supergroup (MMs) of northwestern Canada define an apparent polar wander path lying to the west of the Grenville Loop. This path is suggested from an analysis of the quartzitic Katherine Group, whose probable primary pole lies at the beginning of the sequence, near the younger end of the Grenville Track (0.88 Ga). The end of the apparent polar wander (APW) sequence may be defined by a primary pole from sills intruding the Tsezotene Formation below the Katherine. We relate the sills, dated at about 0.77 Ga, to the rifting event that led to "Copper cycle" and Rapitan sediments above the MMs, and we suggest that the exposed part of the MMs has an age between 0.88 and 0.77 Ga. The APW path is apparently not affected by rotations: pole evidence indicates little if any relative rotation between thrust sheets of the fold belt or between the fold belt and the craton.Paleomagnetic analysis of the Katherine Group data, obtained by alternating field, thermal, and chemical methods, revealed three magnetizations. The probable primary remanence, KA, carried by mainly detrital hematite grains, has a direction of D, I = 267°, +21 °(N = 13 specimens, k = 33, α95 = 7°) and a pole at 9°N, 210°W (δp, δm = 4°, 8°). A secondary component, KB, carried by hematite pigment, has a direction of D, I = 258°, +42 °(N = 4 sites, k = 326, α95 = 5°) and a pole at 17°N, 196°W (δp, δm = 4°, 6°). It documents further a pervasive overprint magnetization found in most MMs rocks. A similar hematite magnetization is probably primary in the overlying Copper cycle rocks. The youngest component, KC, is found partly in a second, probably largely post-folding pigment phase (post-Late Cretaceous or Paleocene) and has a direction of D, I = 007°, +84 °(N = 9 sites, k = 77, α95 = 6°) and a pole at 77°N, 122°W (δp, δm = 11°, 12°).
The determination of magnetization age is fundamental to the understanding and interpretation of paleomagnetic data from metamorphic terranes such as the Grenville Province. Assignment of absolute magnetization ages in slowly cooled rocks, although indeed possible, is difficult in practice due to variability in blocking temperatures of both magnetic and isotopic systems, and in local uplift and cooling rates. Characteristic Grenville paleomagnetic poles of likely post-metamorphic age can be grouped in a relative chronology on the basis of equal age 'thermochron' contours. These pole groups define a post-Keeweenawan loop that can explain the apparently discordant poles without invoking plate collision. As poles postdate the Grenville event, it is unlikely that paleomagnetic data from within the Grenville itself will be useful in testing collisional models for the ca. −1000 Ma orogeny.
The ~1, 100 Myr Grenville mobile belt of the Laurentian (North American) Shield yields a record of uplift magnetisations defining a closed apparent polar wander (APW) loop1–4 nearly identical to the contemporaneous palaeomagnetic records from the Sveconorwegian belt of the Fennoscandian Shield and ~1,100–800 Myr supracrustal successions of the African Shield. The palaeomagnetic data reported here show that these Shields were contiguous at this time4, and comparison with the pre-1,100 Myr palaeomagnetic record defines a relative rotation of the Fennoscandian Shield with respect to the other major shields at ~1,100 Myr, although they remained in close proximity until late Precambrian times. Tectonic and palaeomagnetic correlations between the major shields suggest that this motion represented an early fragmentation of rigid sialic crust. The restriction of crustal mobility to long linear mobile belts and the progressive contraction of anorogenic magmatism both define a gradual consolidation of the Proterozoic crust as temperature gradients declined.
The Eriksfjord Group comprises ∼3000 m of lavas and sediments rapidly deposited in a rift which developed within an Andean-type batholith in juxtaposition to the southern margin of the Laurentian Shield in South Greenland at ca. 1300 Ma. The lavas have been shown to preserve a detailed record of the geomagnetic field at the time of eruption, incorporating normal, reversed and transitional directions. This study has examined the magnetic properties of the intervening red sediments. They are found to possess a diagenetic remanence imparted by mediating fluids at later times. The impact of diagenesis is stratigraphically controlled: the base of the rift infill has magnetizations partially resident in magnetite which are either unstable to thermal cleaning or record a single polarity ‘B’ magnetization (D/I = 284/67°, 31 samples, α95 = 5.5°, palaeopole at 244.1°E, 47.5°N, dp/dm = 7.5/9.1° ). This corresponds in polarity, and closely in direction, to remanence observed in mid-Gardar gabbro giant dykes and dyke swarms emplaced along the axis of the rift system at ca. 1160 Ma; the causative diagenetic magnetite appears to have grown from hydrothermal systems motivated by this magmatism in a sealed reservoir setting within the lower part of the rift infill.
The Ilímaussaq alkaline igneous complex was emplaced into the southern extension of the rift at ca. 1130 Ma and possesses a dual polarity magnetization (D/I = 327/81°, α95 = 6.4°, 10 sites). Eriksfjord lavas within the thermal aureole are overprinted to varying degrees by comparable magnetizations with steep inclinations. The mean pole position (283°E, 71°N, dp/dm = 12/12° ) lies near the apex of an apparent polar wander loop incorporating the Gardar Track (ca. 1300–1140 Ma) and the Keweenawan Track (ca. 1115–1050 Ma). Magnetizations in the Eriksfjord sedimentary succession have not been significantly reset by emplacement of the Ilímaussaq complex, but higher levels of the rift infill are dominated by an ‘A’ magnetization (D/I = 305/34°, α95 = 4.3°, 57 samples, palaeopole at 202.1°E, 32.4°N, dp/dm = 2.8/4.9° ) resident in haematite. The pole position does not correspond with any part of the Gardar Track, but does correlate with the return Keweenawan Track at ca. 1090 Ma, close to the time of Grenville orogenesis along the bordering southeastern margin of the Laurentian Shield. This remanence is attributed to diagenesis during extensional tectonism linked to the collapse of the Grenville Orogen formerly sited 100–200 km to the south.
The 810 Ma Gagwe-Kabuye lavas and the 743 Ma Mbozi gabbro-syenite complex of the Congo Craton in East Africa were sampled for paleomagnetic study in an effort to test a variety of tectonic models proposed for Neoproterozoic times. The paleomagnetic pole obtained from the Gagwe-Kabuye lavas falls at 25°S, 273°E (δp = 7°, δm = 12°) and compares favorably to a previously published paleomagnetic pole obtained from these rocks. The Mbozi complex pole yields a paleomagnetic pole at 46°N, 325°E (δp = 5°, δm = 9°) and differs significantly from a previously determined pole for the Mbozi complex. A comparison of these paleomagnetic poles to Laurentian poles of the same age suggests that the Congo Craton may not have constituted part of the Rodinia supercontinent in the configuration proposed by Dalziel (1992). An analysis of reliable paleomagnetic poles from the Gondwana blocks for the interval from 810 to 510 Ma reveals a coherent swathe of poles from 550 to 510 Ma and a scatter of pre-600 Ma poles. Our interpretation of the available paleomagnetic and tectonic data for this interval is consistent with the formation of Gondwana by two distinct orogenic events. This assembly resulted in the East Africa Orogen between 800 and 650 Ma and a younger Kuunga Orogen at 550 Ma outboard of the East Africa Orogen with possible sutures located in Sri Lanka, southern India and Enderby Land (East Antarctic Craton).
During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value.
A method developed recently for constructing tectonic subsidence curves in early Paleozoic miogeoclines has produced new evidence for the breakup of a late Proterozoic supercontinent. Tectonic subsidence analyses in miogeoclines of eastern and western North America, northwestern Argentina, the Middle East and northwestern Australia limit the timing of the continental breakup to between 625 and 555 Ma. These results refine the implications of a much broader range of radiometric ages of rift-related igneous rocks and biostratigraphic ages of the transition from active extension to passive subsidence in miogeoclines.The recognition of the timing and extent of rifting has led to testable hypotheses for latest Proterozoic and early Paleozoic continental histories. Breakup and onset of drift along an extensive system of continental fractures within a relatively short period of time would generate a large amount of young ocean floor, thereby reducing the volume of the global ocean basin and causing a sea level rise. Maximum reduction of ocean basin volume would postdate the time of breakup, probably by about 70 m.y., placing the transgressive peak at a time not older then about 510–520 Ma. That age agrees well with the time of maximum flooding on the continents close to the end of the Cambrian. Restriction of the breakup to between 625 and 555 Ma reduces the time gap between an essentially intact late Proterozoic supercontinent and the oldest reliable paleomagnetic reconstruction of the dispersed continents at about 560 Ma. A continental reconstruction produced by rotating Laurentia and Baltica into Gondwana a minimum distance from the 560 Ma position is consistent with limited geologic data. However, that reconstruction places Laurentia and Baltica in low latitudes which is difficult to reconcile with the absence of evaporites in syn-rift complexes in both continents.
The upper Proterozoic Windermere Supergroup of western Canada (800-570 Ma) contains the depositional record of a wedening rift system along the evolving passive continental margin of North America. Concomitant fault tectonics affected the cratonic (older than 1750 Ma) crust and superimposed middle Proterozoic pericratonic troughs (dating from about 1600 to 800 Ma). The depositional history of the Windermere Supergroup in Canada (and probably also in the adjacent United States) can be understood in terms of three major shoaling-upwards cycles which are best exposed in the Mackenzie Mountains. The first cycle (Rapitan cycle) contains abundant evidence of faulting contemporaneous with glacial sedimentation. A predominant “proglacial” siltstone facies is overlain by an “ice-marginal” diamictite complex which represents the glaciomarine grounding-line environment of a fluctuating land-based ice sheet. The second cycle (Hay Creek cycle) commences with transgressive black shale or limestone-laminite which grade upsection into a varied and cyclic shallow-water shelf assemblage of clastics and carbonates; the top of this cycle is composed of abundant carbonate olistostromes and oligomictic diamictites which are capped by a thin but regionally persistent shallow-water dolostone. The third cycle (Sheepbed-Backbone Ranges cycle) again commences with black silty shale and is topped by a shallow-water marine to nonmarine dolostone— sandstone succession of sub-Cambrian age. Possible equivalence of these three cycles with similar cycles in the Adelaide Basin of Australia and in the Sinian successions of China suggests that the three basins could have developed along the margins of a complex rift system that led to the opening of an early Paleozoic Pacific Ocean (?) basin.
New palaeomagnetic analyses have been carried out for the Neoproterozoic (650-600 Ma) Elatina Formation, an important redbed unit of the Marinoan glaciogenic sequence in the Adelaide Geosyncline, South Australia, and flat-lying equivalent facies on the adjacent cratonic Stuart Shelf and Torrens Hinge Zone. The Marinoan rocks display strong evidence of marine glacial deposition, and coeval periglacial sand wedges in permafrost regolith on the Stuart Shelf indicate in-situ cold climate near sea level and marked seasonality. The palaeomagnetic data define a palaeopole for the formation and indicate that Marinoan glaciation, including permafrost, grounded glaciers and marine glacial deposition, occurred near the palaeoequator.
Well-dated paleomagnetic poles for the interval 1100–800 Ma have been compiled for the Laurentia, Baltica, São Francisco, Congo and Kalahari cratons in order to construct apparent polar wander paths (APWPs) for this interval. Laurentia's APWP consists of a well-determined Keweenawan track for 1100–1000 Ma and a 1000–800 Ma Grenville loop. We use a counterclockwise APW loop for the Grenville poles based on ages for post-metamorphic cooling through ∼500°C for the Grenville Province between 1000 and 950 Ma, and the temporal and spatial similarities with Proterozoic counterclockwise APWP's for other cratons. Baltica's APWP is comprised of seven dated poles that define a similar loop, counterclockwise and hinged at 950 Ma, that can be superimposed on the Laurentian Grenville loop. This loop is also seen in the seven poles of the APWP for the combined São Francisco–Congo craton; superposition of these loops leads to a reconstruction in which the São Francisco–Congo craton is to the south-southeast of Laurentia in present-day coordinates. A long 1090–985 Ma APWP track for the Kalahari is in reasonable agreement with the roughly coeval Keweenawan track, when the Kalahari craton is rotated ∼40° counterclockwise away from the Congo craton while remaining hinged at the Zambezi belt. The resulting Rodinia reconstruction resembles those previously proposed on geological grounds for Laurentia, East Gondwana, Baltica, São Francisco–Congo, and the Kalahari craton.
Understanding of the style and timing of collision between East and West Gondwanaland to form the East African Orogen is incomplete, but the general outline of this event is slowly emerging. A model embodying the present understanding of this evolution is presented. Present reconstructions of the earliest stages in the EAO orogenic cycle may be more speculation than understanding, but initiation by rifting of a continent is consistent with the data. This rifting is identified as part of the break up of Rodinia at about 850-900 Ma. The sequence of events that begins with sea-floor spreading and formation of arcs and back-arc basins and continues with the accretion of these tectonic cells into juvenile crust is coming into sharper focus, at least for the Arabian-Nubian Shield. There is evidence that these processes were underway as early as 870 Ca and continued until at least 690 Ma. Continental collision first led to crustal thickening and uplift, beginning perhaps as early as 750 Ma but certainly by 700 Ma, and continued with orogenic collapse and escape tectonics until the end of the Precambrian. At least as far as the EAO is concerned, this dates the consolidation of East and West Gondwanaland. Tectonic escape led to the development of major rift basins in the northern EAO and environs which led directly to sea-floor spreading and formation of a passive margin on the remnants of Gondwanaland and the formation of an ocean basin to the north, at about 550 Ma ago. -from Author
The first time-dependent numerical simulations of continental
aggregation and dispersal demonstrate a dynamic feedback between the
motion of continental plates and mantle convection. Plate velocity is
intrinsically episodic. Continental plates aggregate over cold
downwellings and inhibit subduction and mantle cooling; the mantle
overheats and fragments the continent under tension. Overall, the models
are in agreement with the present geophysical state of the mantle and
the geological record over the last 200 million years.