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The making and unmaking of a supercontinent: Rodinia revisited
Abstract
During the Neoproterozoic, a supercontinent commonly referred to as Rodinia, supposedly formed at ca. 1100 Ma and broke apart at around 800–700 Ma. However, continental fits (e.g., Laurentia vs. Australia–Antarctica, Greater India vs. Australia–Antarctica, Amazonian craton [AC] vs. Laurentia, etc.) and the timing of break-up as postulated in a number of influential papers in the early–mid-1990s are at odds with palaeomagnetic data. The new data necessitate an entirely different fit of East Gondwana elements and western Gondwana and call into question the validity of SWEAT, AUSWUS models and other variants. At the same time, the geologic record indicates that Neoproterozoic and early Paleozoic rift margins surrounded Laurentia, while similar-aged collisional belts dissected Gondwana. Collectively, these geologic observations indicate the breakup of one supercontinent followed rapidly by the assembly of another smaller supercontinent (Gondwana). At issue, and what we outline in this paper, is the difficulty in determining the exact geometry of the earlier supercontinent. We discuss the various models that have been proposed and highlight key areas of contention. These include the relationships between the various ‘external’ Rodinian cratons to Laurentia (e.g., Baltica, Siberia and Amazonia), the notion of true polar wander (TPW), the lack of reliable paleomagnetic data and the enigmatic interpretations of the geologic data. Thus, we acknowledge the existence of a Rodinia supercontinent, but we can place only loose constraints on its exact disposition at any point in time.
... 900--850 Ma) was observed in the presented data (Fig. 11). This age gap could be interpreted as a break up of Rodinia and formation of Mozambique ocean (Meert and Torsvik, 2003;Fritz et al., 2013;Hassan et al., 2020) or as long-term passive margins for the region (Bradley, 2008). Ophiolitic rocks in central and southern Eastern Desert assign ages from 890 to 690 Ma (Stern et al., 2004) and probably formed within the Mozambique ocean (Stern, 1994;Azer, 2014). ...
... The third peak of zircon ages ranges from 650 to 580 Ma, with a major peak at 620 Ma. This age may be related to the peak amalgamation of Gondwana at ca. 630 Ma (Meert and Torsvik, 2003;Cawood, 2005;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007). This age is similar to the crystallization ages of the Feiran biotite-hornblende gneisses (632 ± 3 and 623 ± 6; Stern and Manton, 1987;Abu El-Enen and Whitehouse, 2013) and the Ghurabi dioritic and Gnethel quartz dioritic gneisses of the Kid Metamorphic Complex (628 ± 4 and 622 ± 3 Ma; Eyal et al., 2014). ...
... This arc (Fig. 10f) could be related to the latest Mesoproterozoic ocean closure (Be'eri-Shlevin et al., 2012) during the assembly of the Rodinia supercontinent (1300 to 1000 Ma; Rogers and Santosh, 2002;Zhao et al., 2002;Li et al., 2008;Evans and Mitchell, 2011). At nearly 900 to 850, the rifting of the Rodinia supercontinent occurred (Fritz et al., 2013), and as a result, a new oceanic crust, i.e., the Mozambique Ocean (Stern, 1994;Meert and Torsvik, 2003), was developed. Shortly after the formation of the Mozambique Ocean, several subduction zones were initiated (780 Ma; Johnson and Woldehaimanot 2003), leading to the formation of volcanic arcs (i.e., the second arc, Fig. 8c) during the closing of the Mozambique Ocean and initiation of Gondwana assembly. ...
Rodinia to Gondwana evolution record, South Sinai, Egypt: Geological and geochronological constraints
... These periods of mafic dyke and kimberlite pipe emplacement are interesting because they correlate with the formation of the Columbia and Rodinia supercontinents at $1.8-1.6 Ga and $1.1-1.0 Ga, respectively, and may yield insight into tectonic and magnetic phenomena during these major events in Earth's history (e.g., Meert and Torsvik, 2003;Li et al., 2008;Meert, 2012;Santosh, 2017, 2022 ). In recognition that dyke emplacement for individual swarms may take place over several million years (m.y.), we refer to dyke swarms by their average age in billions of years rounded to the nearest ten m.y. ...
... Pisarevsky et al. (2013Pisarevsky et al. ( , 2014a placed India adjacent to Baltica from 1.77 Ga to 1.27 Ga based on paleomagnetic results from the Lakhna dykes emplaced from 1.47 Ga to 1.45 Ga Fig. 13. Rodinia reconstructions at $1.08 Ga (a) and $1.01 Ga (b) based on the rotation of paleomagnetic poles in Table 9 to Earth's spin axis using the closest approach method of Meert and Torsvik (2003). For a detailed explanation of Rotation Parameters, see Supplemental Data (S10-S11 (note that there is no evidence India was unified at this time). ...
... Rodinia's existence as a supercontinent and its foundational configurations are based largely on global Grenvillian (1.1-1.0 Ga) orogenic correlations between continents (Dalziel, 1991(Dalziel, , 1997Hoffman, 1991Hoffman, , 1999Moores, 1991;Rogers, 1996;Torsvik et al., 1996;Weil et al., 1998;Condie, 2001;Meert, 2001Meert, , 2003Meert and Powell, 2001;Meert and Torsvik, 2003;Pesonen et al., 2003;Santosh, 2003, 2004;Torsvik, 2003;Li et al., 2008Li et al., , 2013Bogdanova et al., 2009;Scotese, 2009;Li and Evans, 2011;Evans, 2013Zhao et al., 2018a). However, there are many non-unique solutions when aligning any two orogenic belts (Meert, 2014), including the possibility of one or both being created in an Andean-type margin. ...
Coupled paleomagnetic and geochronologic data derived from mafic dykes provide valuable records of continental movement. To reconstruct the Proterozoic paleogeographic history of Peninsular India, we report paleomagnetic directions and U-Pb zircon ages from twenty-nine mafic dykes in the Eastern Dharwar Craton near Hyderabad. Paleomagnetic analysis yielded clusters of directional data that correspond to dyke swarms at 2.37 Ga, 2.22 Ga, 2.08 Ga, 1.89–1.86 Ga, 1.79 Ga, and a previously undated dual polarity magnetization. We report new positive baked contact tests for the 2.08 Ga swarm and the 1.89–1.86 Ga swarm(s), and a new inverse baked contact test for the 2.08 Ga swarm. Our results promote the 2.08 Ga Dharwar Craton paleomagnetic pole (43.1° N, 184.5° E; A95 = 4.3°) to a reliability score of R = 7 and suggest a position for the Dharwar Craton at 1.79 Ga based on a virtual geomagnetic pole (VGP) at 33.0° N, 347.5° E (a95 = 16.9°, k = 221, N = 2). The new VGP for the Dharwar Craton provides support for the union of the Dharwar, Singhbhum, and Bastar Cratons in the Southern India Block by at least 1.79 Ga. Combined new and published northeast-southwest moderate-steep dual polarity directions from Dharwar Craton dykes define a new paleomagnetic pole at 20.6° N, 233.1° E (A95 = 9.2°, N = 18; R = 5). Two dykes from this group yielded 1.05–1.01 Ga 207Pb/206Pb zircon ages and this range is taken as the age of the new paleomagnetic pole. A comparison of the previously published poles with our new 1.05–1.01 Ga pole shows India shifting from equatorial to higher (southerly) latitudes from 1.08 Ga to 1.01 Ga as a component of Rodinia.
... The former consists of Africa and South America, and the latter consists mainly of East Antarctica, Australia, India, and East Asian blocks (Cawood et al., 2005(Cawood et al., , 2007Gray et al., 2008). During late Neoproterozoic time, those major continental blocks collided with each other due to closure of intervening oceans, forming the Kuunga-Pinjarra (570-530 Ma), , and East African interior orogens (650-620 Ma) (Stern, 1994;Meert, 2003;Cawood et al., 2007Cawood et al., , 2021Li et al., 2008;Torsvick andCocks, 2013, 2017;Zhao et al., 2018). Corresponding to the amalgamation of the Gondwana's interior, roughly coeval subduction and accretion occurred along the periphery of Gondwana, resulting in a series of peripheral orogens, termed the Terra Australis (530-460 Ma), , and North Indo-Australie orogens (500-420 Ma) (Murphy et al., 2000(Murphy et al., , 2013Cawood, 2005;Cawood and Buchan, 2007;Nance et al., 2010;Cawood et al., 2021). ...
... However, this work and latest studies (Yang et al., 2017 have shown that the granulite-facies peak metamorphism of the Jiamusi Block occurred at ~ 560 Ma rather than ~ 500 Ma as previously reported. This metamorphic age is basically consistent with the timing of granulite-facies metamorphism of the Kuunga-Pinjarra Orogen (570-530 Ma) due to the collision of the Australia, East Antarctic, and India (Jacobs et al., 2003;Meert, 2003;Simmat and Raith, 2008;Toyoshima et al., 2008;Dasgupta et al., 2013). Additionally, the Mashan Complex of the Jiamusi Block underwent granulite-facies metamorphism with a clockwise P-T path and the peak conditions are estimated to be 815-870 ℃ and 6.5-9.2 kbar, respectively (Jiang, 1992;Guo et al., 2014;Yang et al., 2020bYang et al., , 2021a. ...
Tectonic evolution from the breakup of the Rodinia supercontinent to the assembly of the Gondwana megacontinent has been well investigated on major continents/cratons. However, the role of microcontinents during the evolution from Rodinia to Gondwana has been poorly discussed. The Jiamusi Block, an important Precambrian microcontinent in the easternmost Central Asian Orogenic Belt (CAOB), is characterized by Pan-African metamorphic records and can be a suitable research objective for reconstructing Gondwana. Here we present a field-based zircon geochronological and Hf isotopic study for the paragneiss of the Mashan Complex in the Jiamusi Block. Four paragneiss samples yielded detrital zircon ages ranging from 2712 to 714 Ma, with the youngest age group of 787, 852, 812, and 915 Ma, respectively. Considering the Neoproterozoic orthogneisses (757, 725, and 898 Ma) intruding the studied paragneisses, we propose that the Mashan Complex contains two sets of supracrustal rocks, with their protoliths deposited at 915–898 Ma and 812–725 Ma, respectively. The metamorphic zircons from the paragneisses yield concordant ages of 566–484 Ma. Considering zircon morphology, internal structures, U-Pb ages, trace elements, and Hf isotopes, we figure out that the metamorphic zircons with ages of 566–560 Ma record granulite-facies metamorphism, which are characterized by high initial Hf isotopic ratios (0.282212–0.282359) and steep chondrite-normalized REE patterns. The 546–484 Ma metamorphic zircons record retrograde metamorphism and exhibit lower initial Hf isotopic ratios (0.281999–0.282204) and relatively flat chondrite-normalized heavy REE patterns.
Based on new data and geological comparison, a unified Bureya-Jiamusi-Khanka Block in the Neoproterozoic is proposed, which was initially originated as part of Northeast India. It was collided with Australia-East Antarctica resulting in the Kuunga-Pinjarra Orogen in the late Pan-African (570–550 Ma). Subsequently, at sometime after 470 Ma, the Jiamusi Block was detached from the Kuunga-Pinjarra Orogen and drifted northward to collide with the Songnen Block of the CAOB in the Middle Jurassic.
... The presented reconstruction here is based on a perceived geometric fitting of coeval mafic magmatic intrusions such as dykes and sills. Here, we use the 'closest approach' technique (Meert and Torsvik, 2003) to bring the cratons into position in our reconstruction. The paleolatitude and azimuthal orientation of each craton/continent is fixed but the paleolongitude and polarity are ambiguous (Meert and Torsvik, 2003;Buchan, 2014). ...
... Here, we use the 'closest approach' technique (Meert and Torsvik, 2003) to bring the cratons into position in our reconstruction. The paleolatitude and azimuthal orientation of each craton/continent is fixed but the paleolongitude and polarity are ambiguous (Meert and Torsvik, 2003;Buchan, 2014). The Euler rotation parameters for the respective paleopoles of each craton are given in Table 3. ...
... Many studies have suggested a strong link between Baltica and Amazonia during the Proterozoic (e.g., [57,62,72,73]. The available information indicates that these continents possibly existed as a single entity in the Nuna and Rodinia supercontinents until Rodinia breakup in the late Neoproterozoic (e.g., [38,63,[74][75][76][77][78][79]. According to most reconstructions, the western margin of Baltica (the Trans-European Suture Zone) was attached to Amazonia, suggesting that the Volyn-Orsha basin possibly continued farther westward towards [70]). ...
... Many studies have suggested a strong link between Baltica and Amazonia during the Proterozoic (e.g., [57,62,72,73]. The available information indicates that these continents possibly existed as a single entity in the Nuna and Rodinia supercontinents until Rodinia breakup in the late Neoproterozoic (e.g., [38,63,[74][75][76][77][78][79]. According to most reconstructions, the western margin of Baltica (the Trans-European Suture Zone) was attached to Amazonia, suggesting that the Volyn-Orsha basin possibly continued farther westward towards Amazonia. ...
We used LA-ICP-MS U-Pb data for detrital zircon to constrain the Maximum Depositional Age (MDA) and provenance of clastic sedimentary rocks of the Volyn-Orsha sedimentary basin, which filled an elongated (~625 x 250 km) depression in SW Baltica and attained ~900 m in thickness. Eighty-six zircons out of one hundred and three yielded concordant dates, with most of them (86%) falling in the time interval between 1655 +/- 3 and 1044 +/- 16 Ma and clustering in two peaks at ca.
1630 and 1230 Ma. The remaining zircons yielded dates older than 1800 Ma. The MDA is defined by a tight group of three zircons with a weighted mean age of 1079 +/- 8Ma. This age corresponds to the time of a ~90 clockwise rotation of Baltica and the formation of the Grenvillian—Sveconorwegian—Sunsas orogenic belts. Subsidence was facilitated by the presence of eclogites derived from subducted oceanic crust. The sediments of the Orsha sub-basin in the northeastern part of the basin were derived from the local crystalline basement, whereas the sediments in the Volyn sub-basin, extending to the margin of Baltica, were transported from the orogen between Laurentia, Baltica and Amazonia.
... In their most recent study, Kulakov et al. (2022), based on new palaeomagnetic and 40 Ar-39 Ar geochronological data, argued that simultaneously with or shortly after the 95°rotation, Baltica did not stay in its secondary position adjacent to Laurentia but instead drifted away (see Kulakov et al. 2022 for more details) latitudinally and probably longitudinally too. In this contribution, we Weil et al. (1998), (c) Pisarevsky et al. (2003), (d) Li et al. (2008), (e) Meert and Torsvik (2003) and (f) Evans (2009). Note that the position of Amazonia is based on palaeomagnetic data from Tohver et al. (2002); Australia and Antarctica were reconstructed using data from Karlstrom et al. (2001) and listed in Meert and Torsvik (2003). ...
... In this contribution, we Weil et al. (1998), (c) Pisarevsky et al. (2003), (d) Li et al. (2008), (e) Meert and Torsvik (2003) and (f) Evans (2009). Note that the position of Amazonia is based on palaeomagnetic data from Tohver et al. (2002); Australia and Antarctica were reconstructed using data from Karlstrom et al. (2001) and listed in Meert and Torsvik (2003). Siberia is not visible in (e) because it is reconstructed on the opposite side of the globe. ...
The core of the Rodinia supercontinent has long been considered to have consisted of three cratons - Baltica, Laurentia, and Amazonia - amalgamated along the late Mesoproterozoic Sveconorwegian, Grenville, and Sunsas orogens. In recent years, however, it has become increasingly clear that the metamorphic and magmatic evolution of the Sveconorwegian orogen is inconsistent with a collisional model. Although geological data alone do not rule out proximity to Rodinia, palaeomagnetic data indicate significant latitudinal separation of Baltica and Laurentia during supercontinent assembly. In this contribution, we briefly review two recently proposed and mutually exclusive tectonic models for the Sveconorwegian orogeny and present a compilation of previously published and new chemical and isotopic data. A lack of crustal thickening throughout much of the orogen and few if any changes in lower-crustal sources and melting conditions between 1.3 and 0.9 Ga suggest that the western part of the Sveconorwegian orogeny represents a change from a dominantly extensional to a compressional back-arc regime, but without a significant change in overall tectonic setting. This orogenic evolution is incompatible with amalgamation into Rodinia and suggests that Baltica may have been isolated until the Silurian Caledonian orogeny.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6627988
... After three decades of research there is still little consensus as to either the duration or configuration of the supercontinent Rodinia (Jing et al., 2020), resulting in many different reconstructions being proposed (see Martin et al., 2020: Fig. 2;Zhao et al., 2021: Fig. 1) The results of our analysis provide no support for the 'traditional model' (Meert and Torsvik, 2003), where South American cratons are attached to Laurentia's eastern margin and Australia/India/east Antarctica is attached to its western margin. Nor does it provide support for variations of this model such as the SWEAT (southwest North Americaeast Antarctica), AUSWUS (Australiawestern United States) or AUSMEX (Australia -Mexico) (see Zhao et al., 2006: Fig. 4). ...
... Weil et al. (1998: Figs. 4B and 5B) and Bettucci et al. (2009) suggested that the Congo-São Francisco and Kalahari cratons formed a block, while Meert and Torsvik (2003), Zhao et al. (2006), andJing et al. (2020: Fig 9D) also included the Amazonia craton. Note that in Fig. 4 West Africa remains attached to Laurentia and separate from other African and South American cratons. ...
... They were coeval with the appearance of the first complex organisms (Ediacaran biota, Xiao and Laflamme, 2009;Pu et al., 2016). In addition, nonactualistic processes have been proposed to explain the Ediacaran paleomagnetic database which shows very fast movements in short periods of time for many cratons (Tanczyk et al., 1987;Meert and Torsvik, 2003;Meert et al., 2007;Klein et al., 2015;Robert et al., 2017, Wen et al., 2020. Explanations to these data comprise extremely fast plate tectonic displacements (McCausland et al., 2007), inertial interchange true polar wander events (IITPW, Robert et al., 2017;2018;Wen et al., 2022) or an anomalous behaviour of the Earth magnetic field, such as an equatorial dipole (Abrajevitch and Van der Voo, 2010;Halls et al., 2015) or strong contributions of the non-dipole field (Van der Voo and Torsvik, 2001;Driscoll, 2016). ...
Anomalous paleomagnetic data have been found worldwide during the Ediacaran period, giving rise to several non-actualistic hypothesis. In order to get more information about this period, paleomagnetic, magnetic fabric and rock magnetic studies were carried out in the Avellaneda Formation ($570-560 Ma) from two drill cores of the Alicia quarry in the Olavarría area of the Tandilia System, in the Río de la Plata craton (Argentina). Anisotropy of magnetic susceptibility studies indicate a pre-tectonic origin for the magnetic fabric of this Formation. Rock magnetic studies suggest the presence of magnetite and hematite in different proportions as the main ferromagnetic minerals carrying the remanence. After step-wise thermal demagnetization, two different characteristic remanence directions were obtained for the same unit, one corresponding to the marls (''b1") of the lower section of the Avellaneda Formation, and the other from the claystones (''b2") of the upper section of this unit. These results were combined with the remanence directions obtained by Franceschinis et al. (2022) for the same unit at La Cabañita quarry, located 10 km away. This procedure allows the calculation of two paleomagnetic poles for the Avellaneda Formation. The AV1 pole is located at: 2.0°S, 311.1°E, A95: 5.0°, N: 58 while the AV2 pole is at: 3.3°N, 348.9°E, A95: 11.7°, N: 7. These results confirms that the Rio de la Plata craton also presents anomalous paleomagnetic data during the Ediacaran, implying extremely fast movements in very short periods of time. This can be interpreted as evidence of two inertial interchange true polar wander events during this time, as was already proposed by other authors. An alternative possibility suggests a non-actualistic behaviour of the Earth Magnetic Field, switching from axial to equatorial positions, with an intermediate stable position between them. The likelihood and implications of these two hypotheses is discussed. Ó
... The geochemical records of Paleoproterozoic Himalayan granite suggest their origin from a single magma or by partial melting of crustal rocks followed by mixing of two or more contrasting magmas (Rao andSharma 2009, 2011;Kumar and Pathak 2010). The presence of Neoproterozoic granite adds to the records of crustal evolution during 1100-900 Ma related to the assembly and growth of Rodinia supercontinent (Meert and Torsvik 2003;Li et al. 2008). Although scanty records are available on Neoproterozoic magmatism in Himalaya, viz., Chor granitoid in Himachal Himalaya (Choubey et al. 1994;, Figure 1. ...
... The intracratonic Illinois Basin covers most of Illinois and parts of western Kentucky and southwestern Indiana. It is bordered by a series of prominent arches and domes ( Fig. 1B) and overlies the northeast extension of the Late Proterozoic to Middle Cambrian Reelfoot Rift system (Kolata & Nelson, 1990) associated with the breakup of supercontinent Rodinia (e.g., Bond et al., 1984;Meert & Torsvik, 2003). Numerous folds, monoclines, and fault zones and systems are present (Fig. 1C), which show a variety of structural styles; the folds and monoclines generally overlie faults in the Precambrian crystalline basement and in several cases, the same structure has undergone deformation under more than one stress regime (Nelson, 1995). ...
The Cambrian (Furongian) Potosi Dolomite (100-183 m) in Illinois is part of the Cambro-Ordovician Knox Group. It is a uniformly dolomitized unit with very low intercrystalline porosity but contains very permeable vug, fracture/cavern porosity intervals. Here, we interpret the characteristics of the widespread porous zones in the Potosi as paleokarst features formed by rising hypogenic basinal/hydrothermal fluids. The conformity bounded Potosi Dolomite is characterized by massive dolomitization, overdolomitization and occlusion of previously generated intercrystalline porosity, void filling mineralization, and extensive dissolution and formation of cavity-conduit systems. The pore spaces are typically lined with drusy quartz or are characterized by partial to complete infilling with chalcedonic silica and/or dolomite cements. Clay minerals may partially fill pore spaces; physical properties and thorium-potassium crossplot suggest chlorite as the main clay mineral present. Dolomite crystals typically are planar-s or nonplanar with open-space filling, inclusion rich saddle dolomite displaying curved and zigzag crystal faces. Void filling cement does not exhibit sign of pressure solution and in places vug porosity is developed along bedding parallel stylolite indicating post burial origin of these features.
Cavern reservoirs in the Potosi are laterally extensive and often stacked with intervening very low porosity dolomite; very low bulk density, excursion of caliper log signature from the baseline, and loss of fluid circulation during drilling in these intervals signify anomalously high porosity and permeability interpreted as being the result of cavern forming multiple paleokarst events. Post burial origin of cavities and void filling cements, association of saddle dolomite and chlorite, and occurrence of Mississippi Valley-type (MVT) ore deposits in Missouri suggest karstification by hypogenic warm basinal/hydrothermal fluids. Dissolution and mineralization likely occurred by flow of deep basinal formation waters and hydrothermal fluids (sourced from the crystalline basement underlying the Reelfoot Rift and the Illinois Basin) along numerous basement-rooted normal, reverse, and strike-slip faults, and the associated fold and fractures. Expansion and contraction because of fault-related seismicity likely developed fracture porosity in brittle host dolomite and possibly ruptured any underling impermeable units to enable large-scale upward and outward fluid movement. The Potosi fracture/cavern porosity intervals are confined by thick very low porosity dolomite intervals that could serve as effective seal. There is no report of any show of oil in the Potosi Dolomite, but the unit has an excellent potential to serve as a combined reservoir and seal for storing anthropogenic CO 2 and waste material.
... Additionally, the EWM plays a significant role in reconstructing the breakup history of the early Neoproterozoic supercontinent Rodinia (Dalziel, 1991;Hoffman, 1991;Li et al., 2008;McMenamin and McMenamin, 1990;Moores, 1991) and the potential existence of the Ediacaran-Cambrian supercontinent Pannotia (Dalziel, 1997;Murphy et al., 2021;Nance et al., 2022;Powell, 1995). The breakup of Rodinia is globally documented through 800-600 Ma rifts that evolved into Cryogenian-Cambrian passive margins (Li et al., 2008;Meert and Torsvik, 2003). However, it has been suggested that present-day North America (Laurentia) remained connected to Amazonia, Patagonia, southernmost Africa, and the EWM until shortly after the final amalgamation of Gondwana, thereby forming the controversial 'short-lived' Pannotia supercontinent (Dalziel, 2014;Nance and Murphy, 2019;Nance et al., 2022). ...
Our current understanding of the Ellsworth Mountains stratigraphy suggests the oldest sedimentary sequence (Heritage Group) was deposited in a Cambrian rift setting. This Early Palaeozoic age is then used as a key piercing point to help define Cambrian paleogeography for the southern paleo-Pacific margin of Gondwana, which places the Ellsworth Mountains between southern Africa and East Antarctica as part of West Gondwana. However, U-Pb zircon dating of a micro-diorite from the Heritage Group reveals a crystallization age of 682 ± 10 Ma, challenging chronostratigraphic and tectonic interpretations. Positive εHft and mantle-like δ18O values for these Cryogenian zircons suggest that the rifting, affecting Mesoproterozoic crust, occurred during the Cryogenian rather than in the Cambrian. This finding strongly supports a connection between the Ellsworth-Whitmore Mountain crustal block and the Transantarctic Mountains in East Antarctica prior to the amalgamation of Gondwana. It also facilitates its contextualization during the breakup of Rodinia, likely positioned close to the Shackleton Range as a continuation of the Australia-Antarctic plate, which separated from Laurentia to form the proto-Pacific Ocean in the late Neoproterozoic. This connection is supported by the U-Pb, Hf, and O data in detrital zircon grains from the lowermost units of the Heritage Group, which indicate local, East Antarctic Shield, and probable Laurentian sources. A second magmatic event in the Cambrian (516 ± 7 Ma) is recorded through zircons from a basaltic andesite within the Liberty Hills Formation, which provides an absolute depositional age for this unit. This magmatism is linked to an extensional setting, albeit distinct from that of the Cryogenian micro-diorite. The Cambrian zircons yield elevated δ18O values, indicating a strong sedimentary influence on the magma source and crustal recycling. We interpret this Cambrian extensional magmatism as a result of a tectonic escape following the collision between the East Antarctic Shield and West Gondwana/Indo-Antarctic plates, leading to the formation of Gondwana. This interpretation argues against the hypothetical Pannotia supercontinent and the proposed Cambrian rift between this sector of the paleo-Pacific margin of Gondwana and southern Laurentia.
... The ANS is the product of 300 million years of continental accretions. In the early Cryogenian, Rodinia has broken (Meert and Torsvik, 2003), proceeding with opening and closing of one or two ocean basins (Collins and Pisarevky, 2005;Stern, 1994), ended by the convergence of East and West Gondwana fragments and the formation of the new supercontinent of greater Gondwana (Stern, 1994). The ANS lies at the northern end of the East-West Gondwana collision zone, known as East Africa Antarctic Orogen (EAAO) (Jacobs and Thomas, 2004). ...
The role of the Red Sea rift on the development and the discrepancy of the seismo-volcanic activity along its flanks is still a debate. Here we tried to resolve this debate by a high-resolution tomographic imaging of the northern Red Sea subsurface structures. For the first time, a large number of arrival time data from the Saudi and Egyptian seismic networks were used. The area comprises the Lunayyir volcanic field in the Saudi Arabia, the Abu-Dabbab seismogenic zone in the Egyptian Red Sea coast, and the Zabargad Shear Zone in the Red Sea. This study revealed clear images of the Red Sea rift-related structures along its flanks. The subsurface extension of the different shear and suture zones existing in the Arabian Nubian shield are well imaged. It is found that the Lunayyir seismo-volcanic activity is possibly controlled by the reactivation of the Yanbu suture zone that is associated with steeply northwestward dipping structure. The suture detachments were observed and identified across the Red Sea as low-V channels. The Egyptian Eastern Desert is found to be highly deformed with crustal-scaled low-V structures which were inherited from the early period of Gondwana collision. The NE-SW strike slip faults along the Red Sea were found to be a part of this deformation that are extended deeply in the crust. The Abu-Dabbab and Marsa-Alam areas were strongly influenced by this deformation with possible magma intrusions. This study provides new insights on the role of the Red Sea in the seismo-volcanic activity along its flanks.
... The exact cause of initiation of the compressive deformation cannot be inferred with full conBdence either. However, the terminal stage of the Mesoproterozoic coincides well with the Grenvillian amalgamation (Deb 2003;Saha and Chaudhuri 2003) related to the formation of the Rodinia supercontinent (HoAman 1991;Mloores 1991;Torsvik et al. 1996;Dalziel et al. 2000;Meert and Torsvik 2003;Rino et al. 2008). The eAect of this compressive event may have manifested in the deformed Chanda Limestone as the far-Beld eAect of the Grenvillian orogeny, characterised by mapscale folds and mesoscopic compressive structures such as thrusts and folds of varying tightness and attitudes. ...
The Mesoproterozoic Penganga Group of Pranhita–Godavari valley basin in south India comprises a succession that starts with a coarse sandstone–conglomerate unit at the base and is successively followed by sandstone, limestone and shale in the order of younging. The complete succession, without any hiatus, is believed to have accumulated during a transgression caused by the progressive deepening of the basin floor as a result of continuous rifting. However, the finding of some stromatolitic limestone at the top of the sequence contradicts the idea of a continuous deepening of the basin. The present study, on the contrary, proves that a phase of deformation induced regression in parts of the basin interjected the regional transgressive phase. The deformational episode caused an uplift of the basin floor and consequent reversal of the basinal slope towards the southwest, which was syn-kinematic to sedimentation. This deformation event triggered sub-marine erosion of the sediments in and around the zone of deformation, while away from it, there is a record of uninterrupted sedimentation. The stromatolitic limestone, deposited on top of the pre-inversion-eroded sediments, is now considered the youngest formation of the Penganga Group.
... Several reconstructions of Rodinia have been proposed (Hoffman, 1991;Weil et al., 1998;D'Agrella-Filho et al., 1998;Tohver et al., 2002;Pisarevsky et al., 2003;Meert and Torsvik, 2003;Li et al., 2008;Evans et al., 2016). The Rodinia configuration proposed by Li et al., (2008) is the most complete, because it includes all cratonic blocks of the world, and it is based on compiled geological information and paleomagnetic data. ...
Here, we discuss the role of the main South American cratonic units in the Columbia and Rodinia supercontinents, and Gondwana megacontinent. According to paleomagnetic and geological data Amazonia and West Africa were linked to Baltica, Laurentia and Siberia forming West Columbia at ca. 1.78-1.75 Ga. The 1.78 to 1.42 Ga paleomagnetic data for Amazonia, Baltica and Laurentia suggest either, that West Columbia preserved its integrity, at least, up to 1.42 Ga, or Amazonia/West Africa broke-up from West Columbia at some time between 1.53 and 1.42 Ga.. On the other hand, the Congo/São Francisco, North China, Rio de la Plata, India and proto-Australia formed the East Columbia at ca. 1.78 Ga. However, the presently available Paleo to Mesoproterozoic paleomagnetic data for these cratonic blocks suggest that East Columbia was short-lived. At 1.1 Ga ago, Amazonia/West Africa, Congo-São Francisco, Kalahari and India probably formed a megacontinent that later collided with Laurentia and Baltica forming Rodinia at ca. 1.0 Ga. Most probably, Rodinia broke-up at ca. 750 Ma, when Congo/São Francisco, Kalahari and other smaller blocks rotated ca. 90° counterclockwise, closing the Brasiliano/Clymene ocean and docked against Amazonia/West Africa and Rio de la Plata at ca. 600-570 Ma ago forming West Gondwana.
... In a recent work (Dey et al., 2022), the provenance analysis of the Krol Sandstone reveals the probable derivation of the sand particles through remobilization of a part of Whyalla Sandstone, a Late Neoproterozoic periglacial aeolian sand sheet deposit preserved in Stuart Shelf of South Australia (Williams, 1998). This conclusion was drawn based on three major evidences (Dey et al., 2022): (1) The dominance of southwesterly flow during deposition of the Krol Sandstone as revealed from the paleocurrent analysis of the well-developed cross-bed sets primarily suggested derivation of the sediments from some landmass located towards northeast; (2) in view of the disposition of the continental blocks, as per the reconstructed configuration of the Rodinia supercontinent during Neoproterozoic (Dalziel, 1997;Meert and Torsvik, 2003;Li et al., 2008) (Fig. 4), the sediments appear to have been derived from the Australian block; and (3) the close similarity in composition, grain-size population, and the U-Pb detrital zircon ages between Krol Sandstone and the Whyalla Sandstone. In view of these findings, the provenance analysis of the mudstone deposit has also become important for the better understanding of the Neoproterozoic paleogeography. ...
... Ga orogenic events and disaggregated during the 0.8-0.6 Ga interval (Hoffman, 1991;Torsvik et al., 1996;Meert and Torsvik, 2003;Li et al., 2008). Weathering and erosion of the 'Grenvillian' mountains, and subsequent development of rift and passive margin successions produced large sedimentary basins across the globe (Bradley, 2011;Rainbird et al., 2017). ...
... Following rifting of the Rodinia continent after ~900 Ma, the Mozambique Ocean opened (Meert and Torsvik, 2003;Li et al., 2008;Hassan et al., 2021) (Fig. 4). Ultramafic-mafic massifs and mélanges dating from 890 to 690 Ma (Stern et al., 2004) (Fig. 4) are widespread in the CED and SED and probably formed in forearc and back-arc basin within the Mozambique Ocean (Stern, 1994;Azer, 2014). ...
... The rift histories of the Fennoscandian, Sarmatian, and Volgo-Uralian cratons are uncertain, but the breakup of Rodinia may have established Tonian passive margins along the southern (Ukrainian Shield area) and northeastern (Timanian or pre-Uralian) sides of Baltica (e.g., Meert and Torsvik, 2003;Evans, 2021;Salminen et al., 2021). van Staal et al. (2021a) proposed that ca. ...
... 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.
... The absence of Mesoproterozoic detrital zircons in the UTY (Fig. 17) indicates there was no sediment supply from the Grenville orogens, which represent a major tectonic domain in the Rodinia supercontinent (Meert, Torsvik, 2003;Li Z.X. et al., 2008;Rainbird et al., 2012;Pessonen et al., 2022, and references therein). ...
Abstract:
Multidisciplinary geochronological, isotopic, chemical, and facial studies in the Malyi Karatau Range (MK) of South Kazakhstan elucidate the Precambrian stratigraphic framework and evolution of the Ishim Middle Tianshan microcontinent (IMT) in the western Central Asian Orogenic Belt. Detrital zircon and apatite U-Pb ages for siliciclastic rocks and chemostratigraphic Sr-C isotopic data for carbonates indicate that they deposited during 800–730 Ma. The sediments are dominated by deeper marine facies in the southwest and shallow marine facies in the northeast. According to paleocurrent indicators, the main provenance located to the west of the basin. Based on the detrital zircon age spectra, the source terrane represented a Paleoproterozoic to Archean crustal block, reworked by an early Neoproterozoic c. 850–720 Ma continental arc. Erosion of Archean and Paleoproterozoic crust is also evidenced by negative eNd values for the sandstones. The petrographic and chemical compositions of the sandstones are consistent with a continental arc source; however anomalously high concentrations of chromium in some layers point to the presence of ultramafic rocks in the source terrane. The ages of metamorphic zircons indicate a high-grade metamorphic event at provenance at c. 2.0 Ga and the ages of detrital apatites suggest
a reset of U-Pb isotope system in apatite at c. 1.8–1.9 Ga. In the early Neoproterozoic, the MK located between the continental arc in the west and the oceanic basin in the east and represented a fore-arc basin. The similarity of the Precambrian magmatic and metamorphic histories and sedimentary facies indicates that the IMT, the Tarim and Yangtze cratons constituted a single Precambrian Ulutau-Tarim-Yangtze Continent (UTY). Judging from the ages of continental arcs that evolved on the northern and southern sides of the UTY, it represented an independent continent at c. 950–840 Ma and was incorporated
in Rodinia at c. 830–820 Ma.
... Many studies have suggested a strong link between Baltica and Amazonia during the Proterozoic (e.g., [56,61,72,73]. The available information indicates that these continents possibly existed as a single entity in Nuna and Rodinia supercontinents until Rodinia breakup in the late Neoproterozoic (e.g., [37,63,74,75,76,77,78,79]. According to most reconstructions, the western margin of Baltica (the Trans-European Suture Zone) 9 of 16 was attached to Amazonia, suggesting that the Volyn-Orsha basin possibly continued farther westward towards Amazonia. ...
We used LA-ICP-MS U-Pb data for detrital zircon to constrain the Maximum Depositional Age (MDA) and provenance of clastic sedimentary rocks of the Volyn-Orsha sedimentary basin, which filled an elongated (~625×250 km) depression in SW Baltica and attained ~900 m in thickness. Eighty-six zircons out of one hundred and three yielded concordant dates, with most of them (86 %) falling in the time interval between 1655 ± 3 and 1044 ± 16 Ma and clustering in two peaks at ca. 1630 and 1230 Ma. The remaining zircons yielded dates older than 1800 Ma. The MDA is defined by a tight group of three zircons with a weighted average age of 1079 ± 8 Ma. This age corresponds to the time of a clockwise ~90° rotation of Baltica and the formation of the Grenvillian – Sveconorwegian – Sunsas orogenic belts. Subsidence was facilitated by the presence of eclogites derived from subducted oceanic crust. The sediments of the Orsha sub-basin in the northeastern part of the basin were derived from the local crystalline basement, whereas the sediments in the Volyn sub-basin, extending to the margin of Baltica, were transported from the orogen between Laurentia, Baltica, and Amazonia.
... In a recent work (Dey et al., 2022), the provenance analysis of the Krol Sandstone reveals the probable derivation of the sand particles through remobilization of a part of Whyalla Sandstone, a Late Neoproterozoic periglacial aeolian sand sheet deposit preserved in Stuart Shelf of South Australia (Williams, 1998). This conclusion was drawn based on three major evidences (Dey et al., 2022): (1) The dominance of southwesterly flow during deposition of the Krol Sandstone as revealed from the paleocurrent analysis of the well-developed cross-bed sets primarily suggested derivation of the sediments from some landmass located towards northeast; (2) in view of the disposition of the continental blocks, as per the reconstructed configuration of the Rodinia supercontinent during Neoproterozoic (Dalziel, 1997;Meert and Torsvik, 2003;Li et al., 2008) (Fig. 4), the sediments appear to have been derived from the Australian block; and (3) the close similarity in composition, grain-size population, and the U-Pb detrital zircon ages between Krol Sandstone and the Whyalla Sandstone. In view of these findings, the provenance analysis of the mudstone deposit has also become important for the better understanding of the Neoproterozoic paleogeography. ...
... Fig. 10b shows the position of the NIB (Aravalli-BGC and Bundelkhand) using the Gwalior pole and the SIB (Dharwar, Bastar and Singhbhum) using the Singhbhum pole. Since longitude is unconstrained, we have placed the blocks in their 'closest approach configuration' (Meert and Torsvik, 2003). Fig. 10b is schematic, and the SIB/NIB could also be quite distant from one another. ...
... Regarding the genealogy of the South American and African cratons, most authors agree on their derivation from Rodinia 21 , except for the case of the São Francisco-Congo craton (Fig. 1). Paleocontinental reconstructions for 1.0 Ga portray the latter either as an isolated landmass [22][23][24][25][26][27] or in the periphery of Rodinia 28-30 . A different view of the Mesoproterozoic paleocontinental scenario was recently put forward [18][19][20] . ...
Western Gondwana amalgamated by collision of continental blocks that did not form prior conjugated margins (extroversion), and by typical Wilson cycles, when continental blocks that rifted away giving birth to new oceans were subsequently re-joined in approximately the same position (introversion). The introverted systems are characterized by the opening of V-shaped basins through rifting and hyperextension of various continental pieces (micro- and ribbon continents) from a former Central African Block. These continental fragments lost substantial parts of their mantle lithosphere and became decratonized while drifting towards the external Goiás-Pharusian ocean. Protracted seafloor spreading and consumption through subduction of the internal and external oceans, respectively, ultimately led to multiple, diachronous collisions with other continental blocks detached from Rodinia (Amazonian, West Africa, Embu, etc.). These collisions pushed the ribbon continents back and closed the introverted basins, squeezing and incorporating the reworked basement tracts between the main colliding blocks and the rigid remainder of the Central African Block (the São Francisco-Congo craton). Continental extrusion and lateral escape tectonics ensued, generating thousands-of-km long networks of anastomosing directional shear zones (keirogens), as a consequence of both the accretionary systems developed between the involved blocks and the highly deformable nature of the decratonized ribbon continents.
... Ga (c-d). Fields were redrawn from Zhao (2002), Meert (2002), Meert and Torsvik (2003), Harley et al. (2013), and Bose et al. (2016). The tectonothermal events identified in the Betul belt largely coincide with the events associated with the assembly and dispersal of the Columbia and Rodinia supercontinents. ...
... The Anadarko Basin was initially part of the Oklahoma Basin (Johnson et al. 1988) which originated in the Early Cambrian in response to thermal subsidence associated with development of the Southern Oklahoma Aulacogen (Wickham 1978;Dalziel 1991;Meert and Torsvik 2003). Cambro-Ordovician carbonate strata accumulated in the axis of the failed rift (Perry 1989) as a broad epicontinental shelf developed on the flanks (Johnson et al. 1989). ...
Upper Devonian and Lower–Middle Mississippian strata of the North American midcontinent are ubiquitously fine-grained and silt-rich, comprising both so-called shale as well as argillaceous limestone (or calcareous siltstone) that accumulated in the Laurentian epeiric sea. Although long recognized as recording marine deposition, the origin and transport of the fine-grained siliciclastic material in these units remains enigmatic because they do not connect to any proximal deltaic feeder systems. Here, we present new data on grain size, whole-rock geochemistry, mineralogy, and U-Pb detrital-zircon geochronology from units across Oklahoma; we then integrate these data with models of surface wind circulation, refined paleogeographic reconstructions, and correlations from the greater midcontinent to test the hypothesis that wind transported the siliciclastic fraction to the marine system. The exclusively very fine silt to very fine sand grain size, clear detrital origin, widespread distribution over large regions of the epeiric sea, Appalachian sources, and paleogeographic setting in the subtropical arid belt far-removed from contemporaneous deltaic feeder systems are most consistent with eolian transport of dust lofted from subaerial delta plains of the greater Appalachian orogen and incorporated into subaqueous depositional systems. Delivery of dust that was minimally chemically weathered to Devono-Mississippian epeiric seas likely provided essential nutrients that stimulated organic productivity in these commonly organic-rich units.
... Palaeomagnetic reconstructions of Rodinia are inherently poorly constrained given later metamorphic overprinting (Meert & Torsvik, 2003;Torsvik, 2003). Historically, the late Mesoproterozoicearly Neoproterozoic proximity of Baltica and Laurentia was accepted based on a rather vague similarity of the Grenvillian and Sveconorwegian segments of the respective apparent polar wander paths (APWPs) (e.g. ...
Late Ediacaran opening of the Iapetus Ocean is typically considered to reflect separation of Baltica and Laurentia during final breakup of the Rodinia supercontinent, with subsequent closure during the Caledonian Orogeny. However, evidence of the pre‐opening juxtaposition of Baltica and Laurentia is limited to purportedly similar apparent polar wander paths and correlation of Rodinia‐forming orogenic events. We show that a range of existing data do not unequivocally support correlation of these orogens, and that geologic and paleomagnetic data instead favor separation of Baltica and Laurentia as early as 1.1–1.2 Ga. Furthermore, new detrital zircon U–Pb age and Ar–Ar thermochronological data from Norway point towards an active western Baltican margin throughout most of the Neoproterozoic and early Paleozoic. These findings are inconsistent with the majority of paleogeographic reconstructions that place Baltica near the core of the Rodinia supercontinent.
... The supercontinent Rodinia is considered to have assembled during Mesoproterozoic to Neoproterozoic (~1300 to 900 Ma), which fragmented later during late Neoproterozoic (Meert and Torsvik, 2003;Li et al., 2008;Cawood et al., 2016). The timing and origin of spatially distributed felsic magmatic rocks of Neoproterozoic time from the Asian terranes provide evidence on the assembly, growth and break-up of the Rodinia supercontinent (e.g., Zhao et al., 2018). ...
The Karakoram Terrane (KT) represents the southern margin of the Eurasian Plate, mainly consisting of Late Jurassic-Early Cretaceous subduction-related granites and post-collisional Miocene leucogranites, which intrude the Late Neo-Proterozoic basement. We report for the first time the existence of the Cryogenian KT basement as recorded from the geochemistry and geochronology of tonalite gneiss (ca. 806 Ma) in the southeastern Karakoram terrane, NW India. Geochemically, the studied tonalite gneiss is slightly peraluminous (Molar Al2O3/CaO+Na2O+K2O=1.1), calc-alkaline volcanic-arc granitoid, strongly fractionated REE (LaN/YbN=33.99), and high Sr/Y =19.75, more akin to its affinity with Tonalite–trondhjemite–granodiorite (TTG)/adakite. The whole-rock elemental data suggest that tonalite gneiss is more likely sourced from ancient mafic lower crust where garnet remained in the residue. The petrogenetic modeling of REE suggests that the melt similar to the observed tonalite gneiss can be generated through ∼50% partial melting of a mafic lower crust with garnet, clinopyroxene, and amphibole assemblage. The synthesis and comparison of present and published Proterozoic magmatic records on the rocks from KT strongly dictate that the produced partial melt similar to observed tonalite gneiss most likely served as the parental melt for the development of TTGs in the Southern Pamir and more evolved granitoid in the Central Tibetan terrane. We propose that the studied tonalite gneiss from the southeast Karakoram is a product of Neoproterozoic Andean-type orogeny formed on the northwestern margin of the Rodinia supercontinent. Thus, our study favors the first time, the position of KT within the Cimmerian belt along with other East Asian continental blocks.
... Relating the similarities between the Paleozoic and Mesozoic geological and fossil records at these locations, Suess (1885) proposed the existence of a supercontinent, Gondwana, which contained South America, Australia, and Antarctica, as suggested by Wegener (1915). The Gondwana amalgamation occurred from approximately 630-550 Ma, with subduction occurring along its proto-Pacific margin at 530 Ma (Dalziel, 1997;Cordani et al., 2003;Meert and Torsvik, 2003;Cawood, 2005;Collins and Pisarevsky, 2005;Cawood and Buchan, 2007;Oriolo et al., 2017) (Fig. 2). ...
The application of potential field methods in regional geophysical studies with orbital data has proven helpful in identifying, modeling, and dimensioning structural features and geophysical signatures in regions of interest. Potential field data, particularly those from gravity satellites, are robust and have a high resolution for regional studies. Therefore, gravity data enable in-depth identification of information from low-frequency sources, interpreted as features with relevant geotectonic significance. Furthermore, by containing wavelengths from low-frequency sources, these data allow investigation of lithospheric depths. However, it is necessary to apply thermal correction because gravity data are affected by thermal anomalies present in the lithosphere. Thus, the greater precision/robustness is attributed to these extensive and heterogeneous areas onshore. In this context, data from the compilation World Gravity Map – 2012 were applied to evaluate the density variation of features in depth and obtain the crust-mantle limit. The three-dimensional (3D) gravity inversion with seismic and seismological constraints was applied to obtain the crust-mantle limit for the onshore and offshore regions of Brazil. Furthermore, our objective was to apply and evaluate a gravity inversion methodology with seismic data constraints for the onshore portion of Brazil, which has an exotic and rich geological setting. The onshore portion is covered by seismographic stations, but has sparse coverage areas, mainly in the Amazonian Craton. In addition, the scarcity of seismic refraction data in the national territory makes it impossible to detail the structure of the base of the crust or lithosphere in a spatialized manner. To obtain the crust-mantle limit, the inversion permits corrections, such as topographic effects, the gravity effect of sediments, and the thermal gravity anomaly correction, which interferes with the investigation of crustal thickness using gravity data. Thus, it was possible to observe shallow Moho depths (~10 km) in the offshore portion and deep (~50 km) in the cratonic regions onshore, equivalent to the depths provided by the deep refraction seismic and receiver function data. Therefore, from the gravity inversion, it was possible to obtain the 3D depth of the Moho, adding information to the seismic interpretations, with the possibility of observing 3D features and profiles that present a resolution compatible with the seismic data. Moreover, we interpreted areas with obliterated signatures owing to thermal anomalies in the heterogeneous continental lithosphere.
... Paleomagnetic studies played a pivotal role in the development of the theory of plate tectonics (e.g., Runcorn, 1956;Irving, 1964;McElhinny, 1973;Tarling, 1983;Khramov, 1987). In more recent times, it facilitated the rapid recognition of the presence of supercontinent cycles in Earth history (Powell et al., 1993;Meert and Torsvik, 2003;Pisarevsky et al., , 2014Li et al., 2008Li et al., , 2019Evans et al., 2016). This in part led to the identification of major true polar wander (TPW) events throughout Earth history (e.g., Kirschvink et al., 1997;Evans et al., 1998;Li et al., 2004), leading to the characterization of geodynamic linkages between the supercontinent cycle and mantle dynamics (Evans, 1998;Li et al., 2004Li et al., , 2008Li et al., , 2022aSteinberger and Torsvik, 2008;Li and Zhong, 2009). ...
The availability of global, uniformly formatted, and easily searchable databases is essential for big data-based and machine-leaning oriented geoscience research. We present a new and data-updated version of the online Global Paleomagnetic Database (GPMDB; http://gpmdb.net/). This version inherits most of the structure from the previous MS Access-based version of McElhinny and Lock (1996), but includes a new RELIABILITY table with Q and R quality factors, as well as the optional inclination shallowing-corrected data where applicable. It now contains 10,021 paleomagnetic poles (994 of them being high quality poles with Q > 5) from 8247 rock units, presented in 4175 publications. The database, publicly available from the GPMDB website, provides a user-friendly graphical interface with the navigation page, an interactive world map showing the localities of all paleomagnetically studied rock units and menu bars. Multi-parameter and multi-stage search of the database is available through a SEARCH menu bar, and users can export the search results as CSV files. We compare the Q and R quality factors for a selection of database entries, and provide examples of database queries. This database will be continuously updated, maintained and improved, providing a unique source of high-quality global paleomagnetic data for a wide range of Earth science research including paleogeographic reconstruction and testing of geodynamic models, and enabling future development of machine learning applications.
... Rodinia Supercontinent amalgamated after the breakdown of Columbia between 1100 to 900 Ma through Grenvillian Orogeny (Li et al. 2008). In the classical Rodinia model, India was connected to Australia and East Antarctica, identical to East Gondwana (Li et al. 1996;Torsvik et al. 1996;Weil et al. 1998) but was later questioned (Fitzsimons 2000;Powell and Pisarevsky 2002;Meert and Torsvik 2003). 771 to 750 Ma palaeomagnetic pole data from Malani Igneous Suits of Western India (Gregory et al. 2009) led Li et al. (2008) to conclude that India never participated in Rodinia Supercontinent. ...
The Meghalaya Gneissic Complex (MGC) of northeast India is a little-studied high-grade metamorphic terrain, located close to the Late Palaeoproterozoic to early Neoproterozoic orogenic front. We include mapping, petrography, mineral chemistry, geochemistry, phase equilibria modelling, and U-Th-total Pb monazite geochronology to investigate the evolutionary history of deformed and metamorphosed ortho- and para-gneisses from the central MGC. The metapelite and metamafic rocks of the MGC are folded to E-W upright, antiforms-synforms; and intruded by charnockites during progressive deformations. Reconstructing the metamorphic history of pelite (garnet-cordierite granulite) and two pyroxene granulite, using a TiMnNCKFMASH and TiNCKFMASHO system, reveals a clockwise P–T path where the peak metamorphism was associated with mid crustal burial heating to granulite facies (~825°C and 5.5 to 6.5 kbar) and subsequent cooling with a minor decompression (~ 816°C and 5.3 kbar). Chemically zoned monazites were grown episodically during 1035 ± 13 Ma (n = 21), 976 ± 14 Ma (n = 16), and 494 ± 14 Ma (n = 26). The granulite metamorphism here initiated at 1035 ± 13 Ma and reached thermal peak at 976 ± 14 Ma. This contribution emphasizes the importance of late Mesoproterozoic to early Neoproterozoic metamorphic evolution of the MGC related to the collision of North and South Indian cratonic blocks. The studied P-T path differs from the previously reported Meso- to early Neoproterozoic paths of Central and Western India and close to Western Australia. This finding further explains the change in the early Neoproterozoic collisional pattern of the Central Indian Suture in extreme east (near MGC) and its significance in reconstructing the western Rodinia.
... Reconstructions of the Rodinia supercontinent are constrained by palaeopole data, and the realignment of the Grenville orogen (c. 1200-980 Ma) belts through North and South America, Antarctica, southern Africa, and India (Powell et al. 1993;Li and Powell 2001;Meert and Powell 2001;Meert 2003;Meert and Torsvik 2003;Torsvik 2003;Tohver et al. 2006;Goodge et al. 2010;Loewy et al. 2011;Torsvik and Robin Cocks 2013;Craddock et al. 2017a;Palin et al. 2018). The break-up of Rodinia (c. ...
Oriented carbonate (calcite twinning strains; n=78 with 2414 twin measurements) and quartzites (finite strains, n=15) were collected around Gondwana to study the deformational history associated with the amalgamation of the supercontinent. The Buzios orogen (545-500 Ma), within interior Gondwana, records the high-grade collisional orogen between São Francisco craton (Brazil) and Congo-Angola craton (Angola-Namibia) and twinning strains in calcsilicates record a SE-NW shortening fabric parallel to thrust transport. Along Gondwana's southern margin, the Saldanian-Ross-Delamerian orogen (590-480 Ma) is marked by a regional unconformity that cuts into deformed Neoproterozoic-Ordovician sedimentary rocks and associated intrusions. Cambrian carbonate is preserved in the central part of the southern Gondwana margin, namely in the Kango inlier of the Cape fold belt and the Ellsworth, Pensacola and Transantarctic Mountains. Paleozoic carbonate is not preserved in the Ventana Mountains, Argentina; Islas Malvinas/Falkland Islands or Tasmania. Twinning strains in these Cambrian carbonate strata and synorogenic veins record a complex, overprinted deformation history with no stable foreland strain reference. The Kurgiakh orogen (490 Ma) along Gondwana's northern margin is also defined by a regional Ordovician unconformity throughout the Himalaya; these rocks record a mix of layer-parallel and layer-normal twinning strains with a likely Himalayan (40 Ma) strain overprint and no autochthonous foreland strain site.
Conversely, the Gondwanide orogen (250 Ma) along Gondwana's southern margin has three foreland (autochthonous) sites for comparison with 59 allochthonous thrust belt strain analyses. From west to east: finite strains from Devonian quartzite preserve a layer-parallel shortening (LPS) strain rotated clockwise in the Ventana Mountains, Argentina; the frontal (calcite twins) and internal (quartzite strains) samples in the Cape belt preserve a LPS fabric that is rotated clockwise from the autochthonous N-S horizontal shortening in the foreland strain site; Falkland Devonian quartzite shows the same clockwise rotation of the LPS fabric; Permian limestone and veins in Tasmania record a thrust transport-parallel LPS fabric. Early amalgamation of Gondwana (Ordovician) is preserved by local layer-parallel and layer-normal strain without evidence of far-field deformation whereas the Gondwanide orogen (Permian) is dominated by layer-parallel shortening, locally rotated by dextral shear along the margin, that propagated across the supercontinent.
... The Anadarko Basin was initially part of the Oklahoma Basin (Johnson et al. 1988) which originated in the Early Cambrian in response to thermal subsidence associated with development of the Southern Oklahoma Aulacogen (Wickham 1978;Dalziel 1991;Meert and Torsvik 2003). Cambro-Ordovician carbonate strata accumulated in the axis of the failed rift (Perry 1989) as a broad epicontinental shelf developed on the flanks (Johnson et al. 1989). ...
... Breakup or dispersal of supercontinents are usually related to large scale continental rift system, LIPs and/or mantle plumes (Meert and Torsvik, 2003;Zhao et al., 2004;Ernst et al., 2008;Ernst, 2014;Li et al., 2008;Evans and Mitchell, 2011;Peace et al., 2020). Although paleomagnetic data suggest fragmentation and breakup of Columbia between 1.3 Ga and 1.2 Ga (Evans and Mitchell, 2011;Ding et al., 2020;Kirscher et al., 2021), the role of these 1.4-1.3 ...
Large-scale continental rifting and large igneous provinces (LIPs) have played important roles in the breakup and dispersal of supercontinents Pangea and Rodinia. Previous paleomagnetic and geological evidence suggests fragmentation of Columbia (or Nuna) supercontinent during 1.4-1.2Ga. However, no large-scale continental rift system has been identified in Columbia during this period, although some continental rifting events between 1.6Ga and 1.2Ga have been reported. Here we provide a refined ca. 1.4Ga paleogeographic reconstruction of Columbia based on previously published paleomagnetic data and geological evidence for connections between continental blocks, and consistent with spatial and temporal distributions of the 1.4-1.3Ga LIPs and smaller intraplate mafic magmatic events interpreted as LIP fragments/remnants. Our results indicate a 1.4–1.3Ga large-scale continental rift zone located along western Laurentia, western-northern Siberia, southeastern Baltica, western-northern West Africa, southwestern Amazonia, southern-eastern Congo/São Francisco, eastern Kalahari, northern North China and northern North Australia. This rift zone extends about 15,000 km across supercontinent Columbia, and is a main indicator and a proximal reason for its final breakup. The spatial distribution of the 1.4-1.3Ga carbonatite-related REE deposits shows that this newly identified rift system also controlled Bayan Obo, the world’s first and largest REE-Nb deposit in northern North China, and Mountain Pass, the world’s second largest REE deposit in western North America. Given the scale of this rift system it can be expected to be the locus of additional carbonatite intrusions as well as other commodity types, and provides important constraints on mechanism and processes for final breakup and dispersal of Columbia supercontinent.
Sedimentary rocks are the only source of information that exists physically to understand the geochemical evolution of Earth’s surface. Its crustal deformation and origination will help to understand the origin, tectonics, and palaeoweathering of clastic deposits. This study explores the same in the Cuddapah Basin (CB), Andhra Pradesh. The composition, provenance, origin, paleo-weathering, and tectonic setting of the basin are analysed using geochemical investigations, such as mineralogical, petrographical, major element, trace, and rare earth elements (REE), suggesting the importance of Nd isotopes as vital indicators of the provenance of sediments, especially in fine-grained sediments where petrography is inadequate. Differentiation between tectonic settings and origin, major elements, trace elements, and REE’s—including Light Rare Earth Elements (LREE) and Heavy Rare Earth Elements (LREE) is carried using predefined ratios, where elemental ratios like Th/Sc, Th/Co, and La/Sc possesses both the higher values (indicating a crustal source) and lower values (indicating a mantle origin). The results also possess a possible felsic provenance: LREE enrichment, a flat HREE pattern, and a negative Eu-Anomaly in the study area. Further, the observed depletion of CaO and Na 2 O in the study area indicates high weathering conditions over time. Discriminant diagrams plotted for Th/Sc Vs La/Sc, Th/Co Vs La/Sc, and Th/Cr Vs La/Cr confirm the materials' felsic origin even further. Thus, the study confirms that the Cuddapah Basin is situated in a Rift-Collisional tectonic setting during the evaluation of the tectonic environment.
Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes. However, it remains unclear whether post‐magmatic thermal events can affect feldspar Pb isotopic ratios. Here, the in situ Pb isotopic composition of feldspar hosted in granitic rocks (thirteen Archean and one Paleoproterozoic) from the northern Kongling terrane, Yangtze Craton, South China, is analyzed. The samples reveal a substantial variation in their Pb isotopic composition, spanning the gap between the 1.9 Ga and present‐day geochrons, which indicates extensive resetting by later tectonothermal events. This resetting was interpreted to have likely resulted from Paleoproterozoic and Neoproterozoic tectonothermal events related to the assembly and breakup of the Columbia and Rodinia supercontinents. These results suggest that Pb isotopes should be used cautiously when tracing magma sources and petrogenesis in magmatic rocks that have experienced post‐magmatic reworking. However, the in situ Pb isotopic composition of feldspar in ancient granitoids may also potentially be used to reveal later tectonothermal events. The extensive resetting of the Pb isotopic composition in feldspar by regional thermal events may also provide new insights into our understanding of the Pb isotope paradox.
The opening and closure of the Paleozoic Iapetus Ocean, leading to the collision of Laurentia and Baltica forming the Caledonian orogen, is one of the prime examples of a Wilson Cycle. In this perspective article, we summarize and discuss the content of 10 new research articles within a 5-stage framework of the Caledonian Wilson cycle from a North Atlantic perspective. Stage 1 covers Neoproterozoic rifting of both the Laurentian and Baltican margins, where the plate tectonic configurations and the timing for the onset of rifting are far from resolved; Stage 2 covers the onset of sea-floor spreading within Iapetus, with several different oceanic basins opening at different times, and with variable geometries of the rifted margins; Stage 3 covers the narrowing of the Iapetus basins along several subduction zones, the number, location and orientation of which are debated; Stage 4 covers the main continent-continent collision, documenting advances in our understanding of (U)HP metamorphism within the Western Gneiss Region; Stage 5 covers post-orogenic extension, transitioning into stage 1 of the subsequent Atlantic Wilson cycle. We review the evolution of the Caledonian Wilson cycle in the light of the recent literature from the past decade and highlight open questions and unresolved issues.
Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle
The Ediacaran apparent polar wander path (APWP) for the Rio de la Plata Craton was analyzed and a new alternative path is presented. This revised path was constructed considering an opposite polarity for poles older than ca. 590 Ma. This path is more consistent with that recently proposed for West Africa, whose large oscillations were attributed to two events of inertial interchange true polar wander (IITPW). A compilation and selection of Ediacaran paleomagnetic data from the main cratons were analyzed leading to a set of global paleogeographic reconstructions throughout the Ediacaran. This model assumes that a "Clymene Ocean" existed between Central Gondwana and West Africa-Amazonia along this period. All cratons with reliable paleo-magnetic information, share similar motions during two time-intervals. The first one (615-590 Ma) can be described by rotation around an Euler pole located in the equator, while the second one (575-565 Ma) by another around an Euler pole on the tropics. Whether these apparent large and fast displacements can be assigned to IITPW events is discussed along with the consistency of considering a large Clymene Ocean during this time.
The Central Indian Tectonic Zone (CITZ) comprised of northern and southern Indian cratonic blocks and is a tectonic window, suitable for investigating the Proterozoic crustal evolution because of the presence of a wide variety of lithologies. Geochemical and geochronological data on mafic granulite by previous workers do not ascertain the possibility of mafic protolith and their coeval link to other CITZ units. Thus, determining precise timing of the formation of mafic granulites may indicate connection between metamorphism and fragmentation of the Columbian supercontinent. This study presents zircon U-Pb ages, Nd isotopes and geochemistry of mafic granulites to evaluate their genesis and timing of metamorphism. Results show tholeiitic affinity and primary magmatic differentiation of parental melt. Depletion in Nb, P, Zr, Ti and positive enrichment in Ba, U and Pb indicate derivation of mafic granulites from variably enriched sub-continental lithospheric mantle (SCLM) source. Zircon U-Pb ages (1564±8Ma-1598±9Ma) are interpreted as period of granulite-facies metamorphism. T DM model ages (2.9-3.4 Ga) of mafic granulites indicate timing of mafic protolith extraction. Mineral isochron age ∼1.0 Ga indicate that these rocks have undergone some events during an early Neoproterozoic period. Protolith of mafic granulites could be related to evolution of melts derived from metasomatized SCLM through fractional crystallization processes.
The carbonate metasediments of Pindwara-AbuRoad Belt (PARB) in the Sirohi district belongs to the Kumbhalgarh Group of the South Delhi Terrane (SDT). The litho-assemblages associated are quartzite, carbonate, mica schist, phyllite, metavolcanics, and granitoids. The present study is made on impure marble and calcsilicates of the study area. The carbonates show mineralogical variations with indiscernible field boundaries. The carbonates composed of calcite, diopside, hornblende, tremolite, actinolite, biotite, muscovite, epidote, quartz, plagioclase with minor proportion of apatite, sphene, garnet, sericite, kyanite, zircon, opaque, and broadly may be termed as calc-silicates. The mineral chemistry, major, trace elements, and REE geochemistry of the carbonates reveal the nature of protolith, provenance, depositional environment, spatial and temporal constraints on metamorphism, and on going tectonic process. The study suggests that the PARB carbonate metasediments were derived from a varied proportion of terrigenous and quartzo-feldspathic felsic provenance and deposited in less saline shallow marine environment in an intra-continental rift setting. These exhibit amphibolite to green-schist facies metamorphism, accompanied by polyphase deformation. The metasediments of the region indicate the Meso-Neoproterozoic transition during the Delhi Orogeny in SDT.
This study explored the relationships between organizational justice perception and commitment among shipyard employees in a maritime organization in Türkiye. Data were collected using two-scale and sociodemographic questionnaires that were answered via email or hand by 290 participants who were shipyard workers in Antalya, Türkiye. The questionnaire included the organizational justice scale consisting of 20 questions, the organizational commitment scale consisting of 18 questions, and 7 questions about demographic characteristics. To analyze the data, IBM SPSS 26 was used. A simple linear regression analysis technique was used to determine the effects between scales. Moreover, interviews were conducted with the employees using the semistructured interview method. It was determined that there was a positive, high-level relationship between organizational justice scale subdimension scores and total scores and this relationship was statistically significant. It was also shown that there was a positive, low-level relationship among the organizational commitment subdimensions' scores of the employees and that the relationship was statistically significant. Regression analysis identified that the organizational justice scale total scores of the employees had a statistically remarkable impact on the organizational commitment scale total scores.
Uplift and exhumation are important factors affecting the preservation of deposits. The anatomy of uplift‐cooling evolution and exhumation in the East Longshou Mountain is of great research value for understanding changes in the Jinchuan Ni‐Cu‐PGE deposit since its formation. This study uses apatite fission track (AFT) thermochronology to reconstruct the thermal history of the East Longshou Mountain, including the Jinchuan mine, revealing the uplift and exhumation history of East Longshou Mountain and elucidating the preservation status of the Jinchuan deposit. The AFT ages in the East Longshou Mountain are distributed from 62.3±3.0–214.7±14 Ma, with significant differences in ages in distinct areas, and the central and pooled ages are consistent within the error range. Inverse thermal history models reveal two rapid cooling events associated with exhumation from the Early Jurassic to the Early Cretaceous (200–100 Ma) and since the Miocene (15–0 Ma), the former attributable to the far‐field response to the closure of the Paleo‐Tethys Ocean and plate assembly at the southern margin of Eurasia, and the latter associated with the initial India‐Eurasia plate collision; a slow cooling event from the Early Cretaceous to the Miocene (100–15 Ma) is thought to be related to the arid environment in northwest China since the Cretaceous. These cooling events have diverse responses and cooling rates in different blocks of the East Longshou Mountain: the southwest and centre of which are mainly cooled at 200–120 Ma and 120–0 Ma, with cooling rates of ∼0.25 and ∼0.33°C/Ma (∼1.25 and ∼0.33°C/Ma in the centre); the Jinchuan mine is mainly cooled at 160–100 Ma, 100–15 Ma, and 15–0 Ma, with cooling rates of ∼1.33, ∼0.25 and ∼2.00°C/Ma. These differentiated coolings imply that the uplift of the East Longshou Mountain before the Miocene (∼15 Ma) was integral. Then strong uplift occurred in the mine area, which is a critical period for the uplift of the Jinchuan deposit to the surface, meaning that the Jinchuan deposit was exposed no earlier than the Miocene (∼15 Ma). According to the mineralization depth obtained by predecessors, combined with the calculation and simulation results of this paper, it can be seen that the bulk of the Jinchuan intrusion may still be preserved at depth.
PRELIMINARY PALEOMAGNETIC DATA FROM THE SIERRA DE LAS ANIMAS COMPLEX, URUGUAY, AND THEIR IMPLICATIONS IN THE GONDWANA
ASSEMBLY
Leda Sánchez Bettucci (*) and Augusto E. Rapalini (**)
(*)Dpto. de Geología,Facultad de Ciencias, Universidad de la República, Uruguay
(**) Laboratorio de Paleomagnetismo D. A. Valencio, Dpto. de Ciencias Geológicas.
Universidad de Buenos Aires
The Sierra de las Animas Complex is a bimodal volcanic and subvolcanic suite exposed in southeastern Uruguay, close to the town of Piriapolis (34.7°S, 55.0°W). It has been assigned to an extensional event which marks the end of the late Proterozoic Brasiliano orogenic cycle. It is represented by syenites, trachytes, rhyolites, ignimbrites, basalts and intercalated sediments. Radimetric dates on different lithologies range from 615 to 490 Ma (Umpierre, 1965 in Bossi, 1966;
Cingolani et al., 1993; Preciozzi et al., 1993; Sanchez Bettucci & Linares, 1996). This complex was sampled for a preliminary paleomagnetic study at 15 sites (87 samples) located on several different localities and lithologies. Paleohorizontal was determined in the field for the basaltic flows (subhorizontal) and the sedimentary rocks (Az. 243° dip 22°). In all other cases sites were assumed as not being tilted, which is likely due to little tectonic disturbance of most
of the outcrops of the Complex.
Samples were submitted to standard stepwise alternating field (AF) and thermal demagnetization. Fourteen to seventeen steps were applied up to fields of 140 mT or temperatures of 700°C. Samples from nine sites showed the presence of stable characteristic remanence. Magnetic components were determined by principal component analysis (Kirschvink, 1980). In most cases component
directions were obtained from 4 or more steps and with maximum angular deviation (MAD) smaller than 7°. Two characteristic magnetic components were determined. One, trending northeast with positive inclinations (and in few cases, southwest negative) was found at sites 6, 7, 8, 9, 12, 13 and 14 (comprising sandstones, basalts, syenites, trachytes and rhyolites). Unblocking temperatures and medium destructive fields values suggest magnetite as the most common
carrier of this component. A paleomagnetic pole was obtained from the mean directions on a sample basis. The location of the pole (SA1) is 19°N, 336°E, dp=7°, dm=11°. Rhyolites from site 14 and co-genetic acid rocks to those from sites 12 and 13 have been respectively dated by Umpierre (1965, in Bossi, 1966) as 519 Ma (whole rock K/Ar) and by Cingolani et al (1993) as 520±5 Ma (Rb/Sr isocrone), suggesting an age of approximately 520 Ma for SA1. Another magnetic component was found at sites 5 (eastward and negative) and 8 (westward and
positive), also isolated in ranges compatible with magnetite as the magnetic carrier.
A paleomagnetic pole (SA2) was computed based on the mean direction from ten samples. Its position is 6°S, 254°E, dp=6°, dm=8°. A radimetric dating from the basaltic rocks sampled at site 5 gave an age of 565±30 (whole rock K/Ar, Sanchez Bettucci and Linares, 1996). An age of 552 Ma is likely for site 8, on the basis of a radimetric dating by Umpierre (1965, in Bossi, 1966). This suggests an age around 560 Ma for SA2.
The positions of SA1 and SA2 are shown in Figure 1 after rotation to a
Gondwana reconstruction (Lottes and Rowley, 1990). Paleomagnetic poles from Australia, India and the Congo Craton for the interval 550-510 Ma, as compiled by Meert et al. (1995) are also shown. These authors proposed that a single APWP can be defined for Gondwana for this interval, suggesting final amalgamation of the supercontinent around 550 Ma. SA1 and SA2 are consistent with this path for their
inferred ages, suggesting that the Rio de la Plata Craton was also part of Gondwana in the Vendian-Cambrian boundary. The age of accretion of this block to other Gondwana blocks can tentatively be suggested as younger than 585 Ma on the basis of the paleomagnetic pole from the Campo Alegre volcanic rocks (D’Agrella and Pacca, 1988) which is not consistent with coeval poles from other Gondwana blocks (Meert et al., 1995).
References
Bossi, J. 1966. Geologia del Uruguay. Departamento de Publicaciones de la Universidad de la República, 365 pp., Montevideo.
Cingolani, C.; Llambias, E.; Varela, R.; Campal, N. and Bossi, J. 1993. Avances sobre la cronoestratigrafía del magmatismo no-orogénico finibrasiliano en el Uruguay: Formaciones Sierra de Animas y Sierra de Ríos. In: Actas de Resúmenes extensos del Primer Simposio Internacional del Neoproterozoico-Cámbrico de la Cuenca del Plata II: 63-68, Montevideo.
D’Agrella, M.S.F. and Pacca, I.G. 1988. Paleomagnetism of the Itajai, Castro and Bon Jardim Groups form southern Brazil. Geophysical Journal, 93: 365-376.
Kirschvink, J.L. 1980. The least-squares and plane and the analysis of paleomagnetic data. Geophys. J.R. Astron. Soc., 67: 699-718
Lottes,A.L and D.B.Rowley; 1990. Reconstruction of the Laurasian and Gondwanan segments of Permian Pangaea. Geol. Soc. Memoir, 12, 383-395.
Meert, J.G., Van der Voo, R. and Ayub, S. 1995. Paleomagnetic investigation of the Neoproterozoic Gagwe lavas and Mbozi complex, Tanzania and the Assembly of Gondwana. Precambrian Research, 74: 225-244.
Preciozzi, F.; Masquelin, H. and Sanchez Bettucci, L. 1993.Geología de la Porción sur del Cinturón Cuchilla de Dionisio. In: Guía de Excursión del Primer Simposio Internacional del Neoproterozoico-Cámbrico de la Cuenca del Plata p.1-39, Montevideo.
Sánchez Bettucci, L and Linares, E. 1996. Primeras edades Potasio-Argón en basaltos del Complejo Sierra de las Animas, Uruguay. In: Actas XIII Congreso Geológico Argentino y III congreso de Exploración de Hidrocarburos I: 399-404
Prior to the Grenvillian continentcontinent collision at about 1.0 Ga, the southern margin of Laurentia was a long-lived convergent margin that extended from Greenland to southern California. The truncation of these 1.8-1.0 Ga orogenic belts in southwestern and northeastern Laurentia suggests that they once extended farther. We propose that Australia contains the continuation of these belts to the southwest and that Baltica was the continuation to the northeast. The combined orogenic system was comparable in length to the modern American Cordilleran or Alpine-Himalayan systems. This plate reconstruction of the Proterozoic supercontinent Rodinia called AUSWUS (Australia-Southwest U.S.) differs from the well-known SWEAT (Southwest U.S.-East Antarctic) reconstruction in that Australia, rather than northern Canada, is adjacent to the southwestern United States. The AUSWUS reconstruction is supported by a distinctive "fingerprint" of geologic similarities and tectonic histories between Australia and the southwestern United States from 1.8 to 0.8 Ga, and by a better agreement between 1.45 and 1.0 Ga paleomagnetic poles for Australia and Laurentia.
The geometrical fit of the continents now separated by oceans has long been discussed in relation to continental drift. This paper describes fits made by numerical methods, with a `least squares' criterion of fit, for the continents around the Atlantic ocean. The best fit is found to be at the 500 fm. contour which lies on the steep part of the continental edge. The root-mean-square errors for fitting Africa to South America, Greenland to Europe and North America to Greenland and Europe are 30 to 90 km. These fits are thought not to be due to chance, though no reliable statistical criteria are available. The fit of the block assembled from South America and Africa to that formed from Europe, North America and Greenland is much poorer. The root-mean-square misfit is about 130 km. These geometrical fits are regarded as a preliminary to a comparison of the stratigraphy, structures, ages and palaeomagnetic results across the joins.
Paleomagnetic results from profuse Middle-Late Proterozoic mafic dyke swarms in southeastern Bahia State (Sa~o Francisco Craton) yield either an easterly direction with high upward inclination or a westerly direction with high downward inclination isolated during AF and/or thermal treatments. Thermal demagnetization behavior and thermochronologic and petrologic considerations indicate that these remanent components originated as primary TRM's. Four groups of directions were distinguished from dykes in spatially distinct areas: Ilheus normal polarity (D = 60.0° I = -68.8° alpha95 = 2.6° N = 17) , Olivença normal polarity (D = 82.4° I = -71.0° alpha95 = 5.1; N = 31), Itajú do Colônia (D = 99.0; I = -71.9 ; alpha95 = 5.9° N = 23) and Olivença reversed polarity (D = 298.8° I = 60.7° alpha95 = 6.4° N = 18), which yield paleomagnetic poles located at 100.4°E 30.3°N (IN), 107.0°E 16.1°N (ON), 111.0°E 7.7°N (IC) and 280.2°E 17.0°N (OR), respectively. These poles define an APW path for the Sa~o Francisco Craton between the time interval 1.01-1.08 Ga which is characterized by at least two polarity intervals.
The Vindhyan Supergroup of central India, the focus of many
paleontological studies, has been reported to contain Cambrian small
shelly fossils, Ediacaran fossils, trace fossils, and Proterozoic
microfossils and carbonaceous megafossils. New U-Pb zircon and
87Sr/ 86Sr isotopic data from the Lower Vindhyan
Supergroup require that the rocks are latest Paleoproterozoic to
earliest Mesoproterozoic in age. Two rhyolitic volcanic horizons from
the Deonar Formation, between the Kajrahat and Rohtasgarh Limestones and
below the unit containing trace fossils, yield U-Pb zircon ages of 1631
± 5 Ma and 1631 ± 1 Ma. The Kajrahat and Rohtasgarh
Limestones of the Semri Group that are below and above the reported
Mesoproterozoic trace fossils have 87Sr/86Sr
ratios of 0.70460 and 0.70479, respectively. The Bhander Limestone from
the Upper Vindhyan Supergroup has an 87Sr/ 86Sr
ratio of 0.70599, consistent with a Neoproterozoic age for this
formation. These results indicate that the Kajrahat Limestone is of
latest Paleoproterozoic age and the Rohtasgarh Limestone is of probable
Mesoproterozoic age. These findings are in conflict with the report of
Cambrian small shelly fossils and fossils of articulate brachiopods in
the Rohtasgarh Limestone and argue for a Mesoproterozoic age for the
formation that contains the alleged trace fossils. Reports of an
Ediacaran fossil Spriggina (?)
from the Lower Vindhyan Supergroup from the northern margin of the
Vindhyan Basin suggest either incorrect stratigraphic correlation of
units or misidentification of this fossil.
The Proterozoic connection between northeastern Siberia and western
Laurentia that we proposed in 1978 is strongly supported by several new
lines of evidence. New age data and refined structural trends in
predrift basement rocks improve the resolution of the fit between the
cratons. The mouth of the large river that is inferred to have provided
the point source for the lower part of the Mesoproterozoic Belt-Purcell
Supergroup in western Laurentia aligns with the Mesoproterozoic Udzha
trough of Siberia. The elbow bend in the Udzha trough bypasses the
Archean Wyoming Province to link the Belt-Purcell basin with
Paleoproterozoic regions in southwest Laurentia having appropriate Nd
crustal-residence ages and zircon crystallization ages to have provided
sources for much of the sediment. The Grenville and Granite-Rhyolite
provinces of southwest Laurentia provide sources for detrital zircons
and felsic volcanic fragments in the east-derived Mesoproterozoic
Mayamkan Formation of Siberia. The ages of mafic sills in the
Sette-Daban region of Siberia overlap those in southwest Laurentia.
Ediacara occur in off-shelf environments on both margins. The two
margins have very similar latest Neoproterozoic earliest Cambrian
rift-drift signatures, including a breakup unconformity and Tommotian
shelf assemblages that record the onset of thermally driven subsidence.
Two possible submarine volcanoes with archeocyathan caps may confirm the
establishment of Early Cambrian seafloor spreading. The Siberian west
Laurentian connection provides better correlations among prerift
terranes than does the southwest United States East Antarctic connection
(SWEAT), and is more compatible with the overall geologic history of
Laurentia and Gondwana.
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 Caledonian nappes in Scandinavia record two main phases of early Paleozoic metamorphism, but their pre-Caledonian tectonothermal history and paleogeographic position are largely unknown. Here we present a U-Pb age of 637+/-3 Ma for metamorphic titanite in the 1776+/-4 Ma (zircon age) Skarja granitic gneiss in northern Sweden. The titanite age is interpreted to represent a Neoproterozoic tectonometamorphic overprint. Geochronologic and paleogeographic considerations suggest that the gneiss was located at the outermost margin of pre-Caledonian (northwest) Baltica and was affected by Neoproterozoic tectonic activity related to terrane accretion, the Baikalian (or Timanian) orogeny, coincident with Cadomian terrane accretion along the Gondwanan margin of northern South America and northwest Africa.
The about 500 km long coastal stretch of central Dronning Maud Land (DML), East Antarctica, is critical for understanding both Gondwana and Rodinia assembly. In common Gondwana reconstructions central DML lies at the potential southern extension of the Mozambique Belt. We report the first extensive geochronological study of magmatic and metamorphic rocks from the area. These new U-Pb SHRIMP zircon and Sm-Nd-data of rocks sampled during the German international GeoMaud 1995/96 expedition indicate that the oldest rocks in central DML are Mesoproterozoic in age. The crystallization ages of metavolcanic rocks were determined at c.1130 Ma. Syn-tectonic granite sheets and plutons give ages of c.1080 Ma, contemporaneous with metamorphic zircon growth at granulite facies conditions. An anorthosite intrusion and a charnockite are dated at c.600 Ma. Subsequent metamorphism is recorded for at least two different episodes at c.570-550 Ma and between 530 to 515 Ma. The latter metamorphic event reached granulite facies and is associated with the syn-tectonic intrusion of a granodiorite body at Conradgebirge. Initial εNd,t-values of the U-Pb dated rocks with crystallization ages around 1.1 Ga range from c. +7 to -4. These values suggest that their magmatic precursors represent variable mixtures of a primitive mantle-derived and continental crust component generated within a mature island arc. Initial Nd isotope data of Cambrian meta-igneous rocks are indistinguishable from the Grenville-age rocks, probably representing partial melts of the Grenville-age basement. The occurrence of Pan-African syn-tectonic granitoids is unique in DML. The structure and shape of this body indicates that the main structural ENE-WSW trend of the region is Pan-African in age and not older, as previously assumed. Some major late ductile sinistral shear zones occurring in the study area fit well in the overall sinistral transpressional setting of the Mozambique Belt. Thus, central DML very probably represents the southern continuation of the Mozambique Belt into East Antarctica.
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
The apex and the western arm of the 1.1-Ga Logan Loop, a prominent
feature of the North American Precambrian apparent polar wander path,
are defined by a large body of data from Keweenawan rocks of the Lake
Superior Basin. Until now the eastern arm of this paleomagnetic feature
has been largely defined by two data points from the Powder Mill Group
of Michigan. A reexamination of this sequence reveals a primary reversed
magnetization which plots close to the apex of the Logan Loop. Data from
the Mellen Complex in Wisconsin, together with our data from the Powder
Mill Group, suggest that for steeply dipping volcanic units, the true
direction of a prefolding reversed magnetization is not obtained by
simple structural rotation about presently observed strike. Reversely
magnetized sites from localities where the Powder Mill volcanics have
shallow dips yield a pole (146°W, 46°N, A95 =
9.2°) on the apex of the loop. A well-defined, stratigraphically
continuous, normal to reversed polarity change near the base of the
Powder Mill Group is not confirmed. Normally magnetized flows have been
found at two localities, only one of which is at the base of the lava
sequence. The higher metamorphic grade of normally magnetized sites
suggests that normal magnetizations within the Powder Mill Group are
secondary and should not be used in definition of the eastern arm of the
Logan Loop.
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.
In the absence of conventional radiometric dating and fossil evidence, magnetostratigraphy is considered to be a very powerful tool to correlate rock formations. Often the magnetozones are used as bench marks in correlation of rocks as the geomagnetic field reversals are ubiquitously synchronous. The Vindhyan sedimentation in the Indian stratigraphy represents a very important time period between 1400-400 Ma with lithounits quite suitable for recovering the geomagnetic field signatures. With the recently obtained results from the Semri Group, palaeomagnetic field during the main Vindhyan Groups namely the Semri, Kaimur, Rewa and Bhander periods is available. It is quite interesting to note that all the formations investigated from these groups reveal both normal and reversed polarities of the palaeomagnetic field. Using this information a magnetic polarity time scale (GPTS) is constructed for the Vindhyan Supergroup during the late Proterozoic. When correlated with the Russian magnetostratigraphic scale for the Riphean period, it is noticed that the geomagnetic field during the late Proterozoic is similar to that of the Phanerozoic with superchrons at some periods and frequent reversals at others throughout the Precambrian.
Potassium-argon and 40Ar/39Ar measurements on samples from six mafic dikes that intrude Precambrian granites in the Seychelles Islands (Indian Ocean) indicate that they crystallized about 620 Ma and were uralitized penecontemporaneously or soon thereafter. Stable paleomagnetic directions from two of the six dikes sampled determine a pole position that, in a Gondwana reconstruction, agrees well with the one reported from the late Precambrian Nama Group in southwestern Africa. The paleomagnetic data thus support previous plate reconstructions of the Seychelles Bank between northern Madagascar and western India, adjacent to the Somali coast of eastern Africa. -Authors
More than 60 individual paleomagnetic poles have been obtained by various workers in the last 20 years from late Precambrian Keweenawan rocks of the Lake Superior region. Nearly all major formations and intrusive units have been subject to at least one paleomagnetic study. Keweenawan rocks thus represent paleomagnetically the world's most intensely studied rock sequence, one that may span a time interval from about 1.2 to 1.0 b.y. ago. The large amount of paleomagnetic data coupled with locally excellent stratigraphic and structural control allows an examination of the extent to which factors other than continental displacement determine the distribution of Precambrian paleopoles. Keweenawan paleomagnetic poles of both normal and reversed polarity plot along a northeast-southwest trending band in the North Central pacific. Stratigraphic and radiometric evidence suggests that within this polar distribution there is a hairpin-shaped path open to the southwest (the so-called Logan Loop) along which there appears to be an anticlockwise polar movement with time. After filtering of the pole population using certain reliability criteria, the width of the better documented western arm of the loop decreases from 20 to 10 degrees of arc along an arc length of about 70 degrees. A smooth narrow polar path is thus produced by selecting those poles for which errors due to sampling density, structural correction, and unremoved secondary components are considered to be a minimum. Although much of the dispersion in pole position may be caused by uncertainties in the paleomagnetic data and associated geological constraints, the gross form of the loop appears to result from two superimposed effects: an apparent movement of the pole relative to the North American continent and a fictitious one arising from a violation in the assumption of a geocentric axial dipole to calculate pole positions. The latter effect is revealed by successive asymmetric reversals that can be explained neither by the presence of an unremoved secondary component nor by continental motion. The Keweenawan apparent polar wander path and that for a contemporaneous sequence from the Grand Canyon, Arizona, agree closely if only normal poles are used. In this case both paths have a similar form to the Logan Loop but are more subdued. While the Keweenawan reversed data also appear to follow an arcuate path, the arc is displaced to the northeast of the normal one as a possible consequence of non-geocentric dipole field behavior. However, both paleointensity and paleosecular variation results from Keweenawan igneous rocks are compatible with the usual assumption of a geocentric dipole and with a change to higher paleolatitudes during times of reversed polarity, but it is possible that some non-geocentric dipole model could also explain these data. Although a regional secondary component can be discounted as the cause of Keweenawan reversal asymmetry, other generally minor components are present with different directions and origins. They may be due to late Keweenawan igneous activity, burial of the Keweenawan sequence, Grenville tectonism, emplacement of copper-bearing ores, and in one instance, possible meteorite impact. Some of these magnetic overprints appear to have formed within a time period of about 1.0 to 0.8 b.y. ago and are thus important as they lie in an age interval poorly represented in North American paleomagnetic data.
Evidence supports the hypothesis that the Laurentian and East Antarctic-Australian cratons were continuous in the late Precambrian and that their Pacific margins formed as a conjugate rift pair. A geometrically acceptable computer-generated reconstruction for the latest Precambrian juxtaposes and aligns the Grenville front that is truncated at the Pacific margin of Laurentia and a closely comparable tectonic boundary in East Antarctica that is truncated along the Weddell Sea margin. Geologic and paleomagnetic evidence also suggests that the Atlantic margin of Laurentia rifted from the proto-Andean margin of South America in earliest Cambrian time. -from Author
Palaeomagnetic samples were collected from sites along a 500 km traverse from the high-grade metamorphic rocks of the central area of the Bushmanland Subprovince near Okiep, to amphibolite facies rocks of the E area of the belt, along the W border of the Kaapvaal Craton. The Namaqua zone pole (Long. = 328oE, Lat. = 8oN, N = 6, K = 20, alpha 95 = 15), is consistent with previously published palaeomagnetic poles for the Okiep Norite and the Noncaip (Konkoonsie) Gabbro, although opposite in polarity to the Okiep remanence. Also reported is a new palaeomagnetic site pole from the Port Edward Charnockite (Long. = 149oE, Lat. = 5oN, n = 6, kappa = 57, alpha 95 = 9), which is also consistent with the Okiep results. Rocks from 4 sites distributed over 200 km along the E margin of the Gordonia Subprovince yield a completely different palaeomagnetic pole (Long. = 203oE, Lat. = 41oS, N = 4, K = 14 alpha 95 = 26). A 1,2 Ga40Ar/39Ar plateau date on cummingtonite from the Jannelsepan amphibolite, suggests that the metamorphic rocks of the E area may have cooled through their magnetic blocking temperatures at a significantly earlier time than the granulites of the central area.-from Authors
A geological traverse across the Aldan shield along the Aldan River shows that the area is underlain by two distinct rock associations. The Middle Aldan association consists of metasedimentary rocks, mainly quartzite, that have been intruded by a potassic biotite granite. Downstream, north of the Middle Aldan association, lies the Lower Aldan association, which consists mostly of charnockite with rafts of older granulite gneiss that contains abundant metasedimentary layers. UPb dating of zircons from the Middle Aldan association granite (1900 Ma) and Lower Aldan association charnockite (maximum age 1918 Ma) and granitic gneiss (maximum age 2230 Ma) shows that the majority of the rocks exposed along the Aldan River are Proterozoic in age. Although they have Proterozic crystallization ages, the granite, granite gneiss and charnockite yield Archean Nd model ages, suggesting that they formed by remobilization—that is, partial or complete remelting—of earlier Archean crust. In contrast, pelitic gneisses included within the charnockites of the Lower Aldan association give Proterozoic Nd model ages, indicating that a substantial amount of Proterozoic rock is incorporated within the Lower Aldan association. The present results show that the rocks along the Aldan River, which are part of the Aldan block, display a significantly different history from those in the Olekma block to the west. The Olekma block contains ca 3.0 Ga greenstone belts Late Archean amphibolite-grade granitic gneisses; the Proterozoic remobilization that typifies the Aldan terrane is absent. The Olekma block was thrust under the Aldan block during the ca 1.9 Ga orogeny contemporaneous with, or slightly after the 1.9 Ga charnockitic event in the Aldan. The 1.9 Ga magmatic and granulite event seen in the Aldan is similar in age and character to the Thelon magmatic zone of northern Canada. This correlation allows the development of a preferred construction for the Precambrian Laurentia-Siberia connection in which the present day southern portion of the Siberia platform was connected to the northern margin of Laurentia.
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.
Vendian to Cambrian age sedimentary rocks of the northern Siberian craton record Early Cambrian rifting from ˜ 543 to 530 Ma and the onset of regional thermal subsidence in early Tommotian time. A similar tectonic history in the Franklinian basin of northern Canada and Greenland supports the possibility that both basins formed conjugate margins. This correlation constrains both the configuration of the Siberia-Laurentia connection, also supported by paleomagnetic and paleoclimatic data from Siberia, and timing of continental breakup, which is further supported by regional trilobite biostratigraphy. Prior to breakup, Siberia and Laurentia formed a coherent continent that rifted from a western landmass (Australia Antarctica India South China) at ˜ 720 Ma, forming a continuous passive margin along western Siberia-Laurentia. Nearly orthogonal to this margin, the 723 Ma Natkusiak volcanic rocks and Franklin dike swarm in northern Canada are suggested to represent a failed rift that extended into Siberia-Laurentia. Subsequent Early Cambrian separation of Siberia-Laurentia was possibly influenced by crustal heterogeneity created by the failed rift.
THE Grenville Province is bounded on the north by the Grenville Front (Fig. 1) and on the south-east by the Appalachian Fold Belt. To the south-west in the St Lawrence Lowlands, Grenville rocks pass beneath sub-horizontal Lower Palaeozoic cover rocks. The Grenville Front is observed to be a fault or metamorphic boundary extending for 1,500 km which truncates several older structural trends. It separates Archaean and Lower and Middle Proterozoic rocks (some of which are unmetamorphosed) to the north from more strongly metamorphosed but generally younger rocks to the south.
Paleomagnetic evidence from 37 sites of the partly red-pigmented siliciclastic Tsezotene Formation supports a recently proposed apparent polar wander path for the Hadrynian Mackenzie Mountains supergroup (MMs). The probable primary remanence has a direction at D°, I°=271, +24 (k=15; alpha950=8) with an associated pole TA (12°N, 214°W N=23 specimens; deltap°=5,9). TA becomes the oldest pole from the MMS. It helps bridge the gap between the apparently youngest poles of the Grenville Loop (about 0.88 Ga) and the suggested younger poles from the MMs. A secondary pole TB (23°N, 198°W N=18 sites; deltap°, deltam°=3,5), derived from a magnetic direction in hematite pigment (D°, I°=263, +48; k=73; alpha95°=4), supports a magnetization found in the overlaying ``Copper cycle'' and in younger units of the MMs as a pervasive overprint. Another secondary pole Tc (63°N, 141°W N=29 sites; deltap°, deltam°=6,6), derived from a magnetization (D°, I°=317, +87; k=89; alpha95°=3) partly residing in another phase of hematite pigment, is of postfolding age (post-Paleocene). This study demonstrates the importance of using several treatment methods, singly and in combination, when analyzing complex magnetizations.
Samples of pre-Karroo dolerites have been collected from twenty sites in Bechuanaland and the Transvaal. After partial demagnetization in alternating magnetic fields, thirteen of the sites give directions of magnetization which form a close group. Some of the dolerites sampled have previously been classified as post-Ventersdorp or post-Transvaal. The measurements show, however, that the majority of the dolerites are post-Waterberg in age. The post-Waterberg diabases are therefore more widespread than had previously been supposed. The mean pole position for these diabases coincides almost exactly with that for the Umkondo dolerites in Rhodesia, and a statistical comparison of the paleomagnetic data confirms the difference between the pole positions is not significant. This agreement strongly supports contemporaneity of the igneous activity in these two regions, which are separated by some 1000 km. It is further suggested that the Umkondo and Waterberg systems should be correlated, which would imply that the ‘post-Waterberg’ igneous activity should be included within the Waterberg system. The age of the Umkondo and Waterberg systems is discussed in the light of the paleomagnetic data and recent age determinations. Paleomagnetic measurements on samples from the kimberlite pipe and dolerite sill in the Premier Mine, north of Pretoria, suggest that the age of this pipe is not Cretaceous, as has previously been supposed, but is also confined within the limits of the Waterberg system.
A paleomagnetic study on 14 red limestone sites of the Helikian Little Dal Group, 'basinal sequence' (Mackenzie Mountains, Northwest Territories, Canada) resolved five magnetizations using thermal and alternating field treatment with vector analysis. One magnetization (C) with low unblocking temperatures (<350oC) is probably a geothite weathering component of Cretaceous age. It gives a direction at 291o, +75o (12 sites, k=73, alpha95=5o) and a pole at 60oN, 170oE. Two other closely related magnetizations (A, detrital?) probably carried by magnetite (AM) and hematite (AH) respectively, yield directions of 265o, -29o(k=87, alpha95=4o) and 264o,-26o(k=53, alpha95=6o) with a combined pole at 16oS, 141oE (14 sites, K= 141, A95=3o). The two remaining magnetizations (B, red hematite pigment?)-a normal (BN) and a reverse (BR) component recognized in most specimens-have a combined direction of 273o,-09o(k=17, alpha95=10o) and a pole at 3oS, 138oE (13 sites, K=26, A95=8o). C and A are prefolding (before Paleocene or pre-late Cretaceous) with A suggested to be primary. A and B lie close to a recently proposed polar track for the late Helikian and Hadrynian and evidence suggests a magnetization age for A of 900 to 950 Ma. -Author
Extensive terranes of basement reactivation are interpreted as resulting from crustal thickening following continental collision. It is suggested that terranes, such as the Grenville Province and much of the Variscan orogenic belt in Europe, have their modern analog in the Tibetan Plateau. The Tibetan Plateau is underlain by a continental crust between 60 and 80 km thick and is characterized by extensive high-potash Neogene vulcanism. Following T. H. Green's arguments that partial melting of a dioritic lower crust may yield potassic granitic liquids and refractory anorthositic residues, we consider that continental collision is followed by crustal thickening, to accommodate further plate convergence, with ensuing partial melting of the lower crust. At high structural levels, silicic-potassic ignimbrites are extruded in intermontane basin-horst terranes, with subjacent granite plutons. At deeper levels, a dry refractory lower crust consisting of pyroxene granulites and anor-thosites is generated.
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.
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.
A paleomagnetic, geochronologic and petrographic study was undertaken on the flat-lying gabbros and basalts of the Nova Floresta Formation of Rondônia state, western Brazil in order to constrain the Mesoproterozoic paleogeography of the Amazon craton. Measurement of the anisotropy of magnetic susceptibility on the gabbroic samples reveals a flat-lying foliation with a radiating pattern of lineations, supporting the field evidence that the gabbros are part of a large, undeformed sill. Petrographic observations of oxides in the gabbros reveals two populations of magnetite grains produced during the original cooling of the sill: large, oxyexsolved titanomagnetite grains and fine-grained magnetite in igneous reaction rims. New 40Ar/39Ar age dating of biotite and plagioclase yield ages of ∼1.2 Ga, which represent the rapid cooling following emplacement of the mafic magma. Whole rock dating of basalt samples yields total gas ages of 1062±3 Ma, similar to the ∼1.0 Ga K/Ar ages reported by previous workers. However, the strong compositional dependence of the age spectrum renders this younger whole rock age unreliable except as a minimum constraint. A single magnetic component is found in the basalts, indistinguishable from the characteristic remanence found in the gabbros that is oriented WNW and steeply upward. This magnetization is considered to be primary and was acquired during the cooling of the sill and associated lavas. A paleomagnetic pole calculated from the Nova Floresta Formation (n=16 sites, Plat.=24.6°N, Plong.=164.6°E, A95=5.5°, Q=5), the first reported pole for the Amazon craton for the 1200–600 Ma Rodinia time period, constrains the paleogeographic position of Amazonia at ∼1.2 Ga. Juxtaposition of the western Amazon craton with the Llano segment of the Laurentia’s Grenville margin causes the NF pole to lie on the 1.2 Ga portion of the combined APWP for Laurentia and Greenland, which indicates that a collision with the Amazon craton could have caused the Llano deformation in early Grenvillian times.
A paleomagnetic investigation of Marinoan glacial and preglacial deposits in Australia was conducted to reevaluate Australia’s paleo- geographic position at the time of glaciation (ca. 610–575 Ma). The paleomagnetic results from the Elatina Formation of the central Flinders Ranges yield the first positive regional- scale fold test (significant at the 99% level), as well as at least three magnetic polarity inter- vals. Stratigraphic discontinuities typical of glacial successions prevent the application of a magnetic polarity stratigraphy to regional cor- relation, but the positive fold test and multiple reversals confirm the previous low paleolati- tude interpretation of these rocks (mean D = 214.9°, I = –14.7°, α95 = 12.7°, paleolatitude = 7.5°). The underlying preglacial Yaltipena For- mation also carries low magnetic inclinations (mean D = 204.0°, I = –16.4°, α95 = 11.0°, paleo- latitude = 8.4°), suggesting that Australia was located at low paleolatitude at the onset of glaciation. The number of magnetic polarity in- tervals present within the Elatina Formation and the Elatina’s lithostratigraphic relation- ship to other Marinoan glacial deposits suggest that glaciation persisted at low latitudes in Aus- tralia for a minimum of several hundreds of thousands to millions of years.
The temporal overlap of 1.69 1.55 Ga westward growth of the Baltic
Shield and voluminous, episodic, 1.65 1.50 Ga rapakivi magmatism in the
Svecofennian domain to the east has long been recognized. New U-Pb data
from southwest Sweden indicate that this westward growth occurred in at
least three distinct stages involving convergent-margin magmatism
(Gothian orogenesis) at 1.69 1.65, 1.62 1.58, and 1.56 1.55 Ga. This
improved resolution along the margin reveals an interesting temporal
correlation between these events and the intracratonic rapakivi
magmatism. Each stage of convergent-margin magmatism was echoed by a
phase of bimodal rapakivi magmatism at 1.65 1.62, 1.58 1.56, and 1.55
1.50 Ga. In addition to this temporal correlation, rapakivi suites form
distinct north-trending arrays that are subparallel to, but 500 1500 km
east of, the active margin. These temporal and spatial links suggest
that recurring subduction along oceanward-stepping zones provided
first-order control(s) on episodic mantle melting and consequent bimodal
rapakivi magmatism in distal, inboard settings. At the very least,
emerging constraints from Baltica do not support previous, purely
anorogenic models for the 1.65 1.50 Ga rapakivi magmatism or models that
singularly implicate lingering effects from the preceding Svecofennian
orogeny.
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.
The Kibaran tectonothermal event in East Africa (1400-1200 Ma) peaked at 1300 Ma and was followed by the emplacement of a linear belt of mafic/ultramafic and felsic plutons between 1275-1220 Ma. A series of the mafic/ ultramafic plutons in Burundi from the Congo craton carry a stable paleomagnetic remanence with a mean direction of , (N = 10 sites, k = 37, ) with a corresponding paleomagnetic pole at 17° S, 113° E. Biotite samples from the Mukanda-Buhoro massif yield well-defined plateau ages averaging and slightly younger integrated ages of . The ages, combined with previously published U-Pb and Rb-Sr ages, suggest that the magnetic directions were acquired during cooling of the massif between 1260-1210 Ma (). One pluton at Nyabikere yields an anomalous direction of , and a corresponding virtual geomagnetic pole at 43° N, 137° E. Hornblendes and biotites from Nyabikere yield younger ages of c. 950 Ma. The magnetization and K-Ar ages in the Nyabikere rocks were reset during a c. 950 Ma thermal event known elsewhere in East Africa. Paleomagnetic poles for the interval 1200-1250 Ma from the Kalahari craton, Congo craton, Laurentia, Baltica, and Australia suggest that the Neoproterozoic supercontinent of Rodinia was not yet fully formed at 1200 Ma. Alternative, previously published supercontinental configurations are not supported by these new paleomagnetic data. Assuming the validity of Rodinia for Late Proterozoic times, this implies that our paleomagnetic results provide evidence for mid-Proterozoic plate movements leading to Grenville-aged collisions (c. 1100-1000 Ma) and the assembly of Rodinia.
The Llano Orogenic Belt along the present southern margin of Laurentia, regarded as continuation of the Grenvillian Orogen along the eastern Laurentian margin and exposed in basement uplifts in central and western Texas, records an similar to 300-m.yr. history of orogenesis culminating in are-continent and continent-continent collision between similar to 1150 and 1120 Ma and continuing until similar to 980 Ma. The shape of the orogen and kinematics of the contractional deformation along the belt, together with the high-P metamorphic conditions attained, indicate that a previously unidentified craton served as an indentor. It is paleomagnetically acceptable for the Kalahari Craton of southern Africa to have been opposed to this margin and within similar to 1500 km of present-day central Texas at similar to 1100 Ma. Moreover, the Kalahari Craton is the correct size, and the structural and metamorphic evolution of the 1200-950 Ma Namaqua-Natal Orogenic Belt that wraps around its present southern margin is compatible with that craton having been the indentor. The ocean basin that closed between the Laurentia and Kalahari Cratons would have been comparable to the present Pacific, with island arc/terrane accretion occurring during the Mesoproterozoic along opposing active convergent margins. The coeval 1.1 Ga Keeweenawan and Umkondo magmatic provinces of Laurentia and Kalahari, respectively, are associated with rifts at a high angle to the Llano and Namaqua Orogens. The rifts are interpreted as the result of collision-generated extensional stresses within the two cratons. The voluminous mafic igneous rocks in both provinces, however, may reflect contemporaneous plume activity. Our reconstruction for 1.1 Ga provides a testable model for the Llano Orogenic Belt of Texas and the Namaqua Orogenic Belt of southwestern Africa as opposite sides of a Himalayan-type collisional orogen, with the Natal Belt of southeastern Africa and the originally continuous Maudheim Belt of East Antarctica as a related Indonesian-type ocean-continent convergence zone. This reconstruction leads to a refinement of the paleogeography of Rodinia, with the Kalahari Craton in a position isolated from both the East Antarctic and Rio de la Plata Cratons by oceanic lithosphere. It also provides the first model for the assembly of that hypothetical early Neoproterozoic supercontinent. At least four separate cratonic entities appear to have collided along three discrete segments of the apparently anastomosing global network of "Grenvillian" orogens: the type-Grenville Belt of eastern North America and counterparts in South America, the Llano-Namaqua Belt, and the Eastern Ghats-Albany/Fraser Belt of India-East Antarctica and Australia. Over the remarkably short interval of similar to 200 m.yr., this first-order composite collisional event resulted in the amalgamation of most of Earth's continental lithosphere and defined the close of the Mesoproterozoic Era.
New paleomagnetic and age data from the Sinyai metadolerite dike in central Kenya support the suggestion that the eastern portion of Gondwana was assembled during two separate orogenic events. The dike intrudes Mozambique Belt metasediments dated Ma and was itself metamorphosed to greenschist facies at Ma. This greenschist-facies event reset the original magnetization in the rocks and occurred over a time span that included at least one field reversal. The paleomagnetic pole at 20°S, 319°E () augments the available paleomagnetic database for Gondwana and suggests that Gondwana assembly was completed by 550 Ma; therefore the concept of a united East Gondwana continent may not be valid for pre-550 Ma time. In our model, the 650-800 Ma East Africa Orogeny resulted from a collision between the Congo craton of East Africa and the IMSLEK terranes (India, Madagascar, Sri Lanka, Enderby Land, and the Kalahari craton). A pervasive granulate-facies metamorphis event at Ma in parts of East Gondwana, coupled with our paleomagnetic evidence for a united Gondwana at 550 Ma, led to our suggestion of a Kuunga Orogeny at this time. The Kuunga Orogeny results from the collision of Australo-Antarctica with Congo-IMSLEK.
A detailed paleomagnetic contact test is conducted for a mafic dike and its tonalitic gneiss host rock in the Precambrian Grenville Province of Canada. The measured anisotropy of laboratory-induced thermoremanent magnetization (TRM) is used to correct the directions of natural remanent magnetization (NRM) in the country rock for assumed deflection by the strong magnetic anisotropy due to the rock fabric. Multidomain magnetic minerals rather than single-domain minerals appear to control the anisotropy. After anisotropy correction, NRM directions from the baked gneiss near the dike contact agree well with the NRM directions from the chilled margin of the early Cambrian dike. The NRM of the dike is determined to be primary. It is unlikely that there was post-emplacement tectonic movement of the dike. The dike may have cooled and TRM may have been acquired during a geomagnetic field excursion due to its geologically short cooling (blocking) period of several tens of years.
A stable remanence was isolated from three groups of rocks collected in the Eastern Desert of Egypt. Two groups of dikes, one collected orth of the Qena-Safaga road and the other about 20 km to the south near the Um Rus gold mine, gave paleomagnetic pole positions of 87°N, 304°E and 86°N, 185°E, respectively. Both have K/Ar ages in the range 480-530 m.y. The results are compatible with data reported from other Gondwana cratonic areas for this time period. The third group of rocks were samples of the Dokhan Volcanic Series collected at seven sites along the Qena-Safaga road. The paleomagnetic pole position of the higher-coercivity component, 36°S, 17°E, acquired about 600 m.y. ago is not easily reconciled with established polar wander paths. The younger component, however, with a paleomagnetic pole lying at 54°N, 327°E, suggests a Cambro-Ordovician age.
Chemical, thermal, and alternating field (af) treatments performed on 257 specimens (37 sites) of the Jacobsville Formation show that the magnetization was acquired gradually over a very long period of time. Three phases of magnetization can be recognized and sequentially separated chemically. Thermal (up to 675øC) and af (up to 290 mT) treatments are unable to distinguish and separate the first two phases. The results are consistent with a three-phase magnetization model previously proposed and again demonstrate the necessity of performing chemical leaching experiments in red bed studies. The early phase remanence isolated chemically indicates that the Jacobsville is of upper Keweenawan age (- 1100 m.y.). Poles obtained from three areas, Sault Ste. Marie (SSM) (175øE, 12øN), Marquette (182øE, 03øS), and the Keweenaw Peninsula (KP)(184øE, 10øS), indicate that the sediments of SSM are older than those of KP. A detailed study (nine sites: mean pole at 190øE, 16øS) of a 5.3-m stratigraphic section at Jacobsville shows significant apparent polar motion and the occurrence of at least one field reversal. The trend of the pole movement relative to North America was then southward. Vector analyses show that during the acquisition of the intermediate and late phase remanences the apparent pole started to move northward; by the end of the magnetization process it had reached high latitude (307øE, 72øN). Explanation of the Jacobsville results and other high-latitude poles requires a major revision of the apparent polar path during the Hadrynian. The proposed path executes a loop into the southern hemisphere (- l100 to -950 m.y.) and then roughly follows a great circle path (Hadrynian Track) from 160øE near the equator up to the present north geographic pole and down to the equator at 340øE (-670 m.y.). The controversial Grenville poles could easily be incorporated into that loop, supporting the hypothesis that the Grenville Province has always been an integral part of Laurentia. The ttadrynian Track, with its large pole displacement (180 ø in 300 m.y.), is an extremely useful stratigraphic tool that can be used to great advantage for global correlations of late Precambrian rock units.
Paleomagnetic results demonstrate that during the Cambrian the South China block was close to the equator. We suggest that it was adjacent to North Australia. This reconstruction juxtaposes Cambrian marine basins in South China and Australia, explaining the affinity between Cambrian trilobites from the two areas, as well as the existence of phosphorite deposits in the Early and Middle Cambrian in Australia and in South China. The stratigraphic similarity between the late Precambrian Sinian System in South China and the Adelaide System in Australia, and the continuing fossil affinities from Cambrian through Ordovician of both areas suggest that the proposed geographic configuration lasted from the late Precambrian (800 Ma) to Early Ordovician (470 Ma). Paleomagnetic results from the Cambrian of North China indicate that it was in the southern hemisphere at that time. Based on the paleontological evidence, we suggest that the North China block was close to Tibet, Iran and northern India during the Paleozoic.
New palaeomagnetic data from the Neoproterozoic felsic volcanic rocks of the Malani igneous suite (MIS) in NW India, combined with data from an earlier study, yield a palaeomagnetic pole with latitude=74.5°N, longitude=71.2°E (dp/dm=7.4/9.7°). A statistically positive fold test and remanences carried by typical high-temperature oxidation (deuteric) minerals support a primary magnetic signature. U/Pb ages from MIS (771–751 Ma) overlap with those for granitoids and dolerite dykes from the Seychelles microcontinent (mainly 748–755 Ma), and palaeomagnetic data for both entities can be matched with a tight reconstruction fit (Seychelles→India: Euler latitude=25.8°N, longitude=330°E, rotation angle=28°). In this Neoproterozoic time interval, MIS and the Seychelles must have been located at intermediate northerly latitudes along the western margin of Rodinia, with magmatism that probably originated in a continental arc.The most reliable, dated palaeomagnetic data (±756 Ma) from MIS, Seychelles and Australia require a crucial reappraisal of the timing and plate dynamics of Rodinia break-up and Gondwana assemblage. These new data necessitate an entirely different fit of East Gondwana elements than previously proposed, and also call to question the validity of the Southwest US–East Antarctic and Australia–Southwest US models. The palaeomagnetic data mandate that Greater India was located west of Australia rather than forming a conjugate margin with East Antarctica in the Mid-Neoptroterozoic. Break-up of Rodinia along western Laurentia may therefore have taken place along two major Neoproterozoic rifts; one leading to separation of Laurentia and Australia–East Antarctica, and the second between Australia and India.
A palaeomagnetic and anisotropy of magnetic susceptibility (AMS) study has been performed on dolerite sills of the Central Scandinavian Dolerite Group (CSDG) in the Fennoscandian Shield. The dolerites occur in four previously known complexes in central Sweden and Finland and from the results of this palaeomagnetic study another complex has been identified in northern Sweden. These complexes cover an area of at least 100 000 km2 and the palaeomagnetic data suggest a small difference in time between the intrusion of the dolerites. The measurements of anisotropy of magnetic susceptibility reveal a magnetic fabric with almost horizontal foliation planes and lineations that indicate fairly uniform ca NW or SE directed magma flows. The dolerites of the CSDG are geochemically rather uniform and have compositions typical of mantle derived melts formed in continental tensional settings. In a palaeomagnetic reconstruction of Baltica versus Laurentia at ca 1.27 Ga the two continents were joined, with NE Greenland attached to NW Baltica. AMS data from a few dolerites and a basalt in NE Greenland indicate magma flow directions that in the tectonic reconstruction are more or less parallel to the flow of the dolerites in Sweden. This may suggest a common magma source located at the reconstructed contact between Baltica and Laurentia. Both the dolerites in Greenland and those in Sweden are of tholeitic composition indicating an intraplate origin, which supports the interpretation of joined continents at that time. The tensional regime, that is reflected by the huge sill complexes, is in our interpretation related to the break up of Baltica from Laurentia at ca 1.27 Ga ago.
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.
Palaeomagnetic results from nine sites of alkaline dykes in the Harohalli area, Dharwar craton, south India, provide the best palaeomagnetic pole for the Indian shield during 850-800 Ma. The mean palaeomagnetic direction is D = 7.4°; I = 81.5°; n = 9; κ = 46; α95 = 7.7°) yielding a pole position at λ = 28°S; ϕ = 260°E (dp/dm = 14/15°). The results for the Harohalli dykes, together with earlier results, define a motion of the Indian subcontinent between ∼1000 and 500 Ma and constrain an important geotectonic process between India and Africa during this period. While the 850-800 Ma Indian pole differs from the African pole for the same period in the Lotts and Rowley (1990) reconstruction, the Indian and African poles for 800-700 Ma and 650-500 Ma demonstrate excellent agreement. Thus, we suggest juxtaposition and collision between the African and the Indian continental nucleii along the Mozambique Belt (MB) to have occurred in the latest Precambrian (∼800-750 Ma). Integration of our results with recent geochronological and petrological investigations in the then neighbouring Gondwana segments (India, Sri Lanka, Antarctica and Africa) helps to evaluate recently suggested geotectonic correlations between these fragments in the latest Precambrian. The south Indian granulite region extending up to the Bhavani shear zone could represent an independent Palaeoproterozoic terrane (SIGT) distinctive from the east coast region of India including the Eastern Ghat Mobile Belt (EGMB). The missing seafloor of the ‘Mozambique Ocean’ seems to have been consumed initially during the Late Precambrian (∼800-750 Ma) by collision between Africa and the south Indian shield along the MB. The orogenic activity gradually migrated with time into the Highland/Southwestern Complex (HSWC) of Sri Lanka (∼600-550 Ma) and then into the Lützow-Holm Complex (LHC) of Antarctica (∼550-520 Ma) giving rise to final amalgamation of the continental blocks to form the Gondwana supercontinent.