Rodinia Supercontinent Research Articles

Discussion on ‘From Pan-African transpression to Cadomian transtension at the West African margin: new U–Pb zircon ages from the Eastern Saghro Inlier (Anti-Atlas, Morocco)’ by Errami et al . 2020 ( SP 503, 209–233)

An important paper has recently been published in Geological Society, London, Special Publications by Errami et al . (2020). On the basis of new U–Pb zircon radiometric data on magmatic and sedimentary rocks in the Saghro Massif, the authors revised the history of magmatic and geodynamic evolution of the Pan-African belts of the Moroccan Anti-Atlas along the northern edge of the West African Craton. The authors focused on the two main accretionary stages widely recognized in the Anti-Atlas (Ennih and Liegeois 2008; Gasquet et al. 2008): (1) a Paleoproterozoic episode, known as the Eburnean Orogeny, characterized by the extensive emplacement of granitoids at c. 2.1 − 2.0 Ga; (2) Neoproterozoic (800–450 Ma) events corresponding to the Pan-African Orogeny. However, in their lithostratigraphic framework of Proterozoic units of the Anti-Atlas, the authors do not account for the magmatic event recently recognized in several inliers in the Anti-Atlas (Fig. 1): Ighrem (Ikenne et al. 2017), Kerdous (Youbi et al. 2019) and Zenaga (Ait Lahna et al. 2020). Sills intrusive into the mixed carbonate–siliciclastic series of the Taghddout and Lkest groups, previously considered as Cryogenian, have been dated at between 1.7 and 1.6 Ga (Fig. 2). These new ages are c . 1 Ga older than previously thought, and call into question the stratigraphic position of the Tagdoute and Lkest groups in the southwestern domain of the Anti-Atlas. These series are now interpreted to be deposited in an intracratonic basin that developed after the assembly of the Nuna–Columbia supercontinent and before the break-up of the Rodinia supercontinent. The previous Cryogenian age for these deposits and their geodynamic setting thus need to be revised. Fig. 1. Geological map of the Anti-Atlas with the locations of the dated sills in the Ighrem, Kerdous and Zenaga inliers shown. SAF, South Atlas Fault; WAC, West African Craton; AVFZ, Ameln Valley Fault Zone; TTFZ, …

Metamorphic P–T–t–d evolution of the Mesoproterozoic Pur‐Banera supracrustal belt, Aravalli Craton, northwestern India: Insights from phase equilibria modelling and zircon–monazite geochronology of metapelites

AbstractThe Pur‐Banera belt of metasedimentary rocks, in the Bhilwara region of the Aravalli Craton, northwestern India, constitutes a Mesoproterozoic rift‐related supracrustal sequence. The Pur‐Banera belt, while containing psammitic, calcareous, and ferruginous metasediments, is dominated by garnet–staurolite–kyanite‐bearing metapelites. Here we integrate data on outcrop‐ and microscopic‐scale deformation structures with pseudosection modelling and zircon–monazite geochronology to decipher the P–T–t–d evolution of these metapelites. The metapelites record three distinct deformation events. The first two (D1–D2) produced a composite S1//S2 foliation, and a younger event of dextral shearing (D3) produced crenulations superimposed on the foliation. Textural and compositional data indicate two stages of growth of garnet, whose core compositions were significantly altered during peak metamorphism. The textures combined with pseudosection modelling and conventional thermobarometry reveal that the garnet cores continued to grow up to staurolite‐grade prograde metamorphism, followed by a second stage of garnet growth (syn‐D2; 7.3–7.9 kbar and 665–690°C) during kyanite‐grade peak metamorphism. Fibrolite grew in the matrix during post‐peak readjustments due to uplift and decompression, whereas fluid‐induced retrograde metamorphism (480–540°C) resulted in the formation of euhedral staurolite prisms and narrow rims around garnet porphyroblasts. Detrital zircons of magmatic origin yield a weighted mean 207Pb/206Pb age of 1,827 ± 7 Ma (95% confidence) indicating a Palaeoproterozoic igneous source rock for the sediments, consistent with a Mesoproterozoic (1.6–1.3 Ga) age of deposition as inferred in previous work on the Pur‐Banera quartzofeldspathic gneisses. Monazite U–Th–(total) Pb ages indicate the timing of commencement of prograde metamorphism at c. 1.3 Ga, peak metamorphism at c. 1.2–1.1 Ga, and fluid‐induced retrograde metamorphism at c. 0.85–0.75 Ga. Our combined results indicate that the metapelites experienced two deformation events (D1 and D2) during the closure of the Pur‐Banera basin and the consequent burial of the sediments to lower crustal depths. These were followed by post‐collisional uplift and exhumation, and fluid‐induced retrograde metamorphism during D3 shearing. Southwestward tilting of the rocks during the D3 event, and subsequent erosion, have exposed rock units in the western, central, and southeastern parts of the belt which were buried deeper than those in the southwestern parts. This explains the observed northeastward increase in the metamorphic field gradient along the NE–SW strike of the belt. These new insights into the Meso‐ to Neoproterozoic tectonometamorphic evolution of the Pur‐Banera belt help relate it to the amalgamation and fragmentation of the supercontinent Rodinia.

Early Neoproterozoic continuous oceanic subduction along the northern margin of the Tarim Block: Insights from ca. 910–870 Ma arc-related magmatism in the Aksu area, NW China

The Tarim Block in NW China records the tectonic transition from compression to extension during the Neoproterozoic, and hence is regarded as a component of the Rodinia supercontinent. To unravel the role of the Tarim Block in the Rodinia assembly during the early Neoproterozoic, new geochronological and geochemical analyses were conducted on the gabbroic diorite, plagiogranite and andesite exposed in the Aksu area, northwestern Tarim. Zircon U-Pb dating indicates that these magmatic rocks were formed at ca. 900–870 Ma. Geochemically, these magmatic assemblages have typical features of arc-type rocks, showing enrichment of LILEs and depletion of HFSEs (such as Nb, Ta and Ti). They all have positive zircon εHf(t) values (+6.8 to +12.7), positive εNd(t) values (+3.6 to +6.0), and low and constant (87Sr/86Sr)i ratios (0.70252 to 0.70485). The gabbroic diorites display geochemical features of boninitic rocks such as high SiO2 (53.4–56.3 wt%), MgO (5.79–9.15 wt%), low TiO2 (0.29–0.41 wt%) contents, indicating that they were derived by partial melting of residual mantle. The plagiogranites are characterized by high SiO2 (74.7–79.6 wt%), Na2O (3.87–4.74 wt%), moderate Al2O3 (11.5–13.2 wt%), low K2O (0.15–0.22 wt%) contents, with very low TiO2 (0.08–0.17 wt%) and total REEs (6.3–19.0 ppm) contents similar to oceanic plagiogranite, indicating a hydrous low-pressure melting of mafic protolith. The positive εNd(t) and zircon εHf(t) values and low (87Sr/86Sr)i ratios of the andesitic rocks in the Aksu area suggest a depleted mantle origin. The analysis of trace elements (e.g. Th, Zr, Nb) of these intrusive and volcanic rocks in the Aksu area indicates that their magma sources had been metasomatized by slab-derived fluids. Combined with trace element features, we infer that these early Neoproterozoic magmatic rocks in the Aksu area developed in an oceanic subduction setting with arc-back-arc system probably analogous to the Izu-Bonin (IB) subduction system in the western Pacific. These findings lead us to propose that continuous oceanic subduction beneath the northern margin of the Tarim Block occurred during ca. 910–870 Ma, corresponding to the Neoproterozoic circum-Rodinia subduction-accretion system, which provides new evidence for the accretionary process of the Tarim Block to Rodinia during the early Neoproterozoic.

The largest negative carbon isotope excursions in Neoproterozoic carbonates caused by recycled carbonatite volcanic ash

The late Ediacaran Shuram Excursion (SE) records the most prominent negative δ13C excursions (δ13C = −12‰) during Earth’s history. It has been hypothesized to have resulted from oxidation of dissolved organic matter, diagenetic or authigenic precipitates. However, the origin of the SE remains enigmatic; current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions. Here, we show that the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the SE event, contains mineralogical and geochemical signatures related to igneous processes. Both the occurrence of ankerite, feldspar, moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source. In particular, the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks. These observations suggest that the deep cycle of ancient carbonate rocks, which were subjected to decarbonation during subduction, melting and eruption related to the breakup of the Rodinia supercontinent, contributed to the SE. This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth.

Granites and gabbros at the dawn of a coherent Australian continent

The Rudall Province in Western Australia is a key crustal component in the amalgamation of the Rodinia supercontinent. New field observations, U–Pb zircon geochronology and geochemistry identify three previously unrecognised Mesoproterozoic magmatic events in the eastern Rudall Province. The Kayilirra Suite formed at ca. 1500 Ma and is a magnesian, calc-alkalic to alkali-calcic and weakly peraluminous suite with a limited SiO2 range of 69–70 wt%. The suite is interpreted to have formed in either a post-tectonic or rift-related setting. The Kalyukuyarra Suite formed at ca. 1185–1165 Ma and was synchronous with a peak in magmatic activity in the along-strike Musgrave Province. The suite is magnesian to ferroan, alkali-calcic and calc-alkalic, high K and peraluminous. Abundant inherited zircon grains indicate a dominantly crustal origin for the suite with only minor interpreted mantle input. Newly identified mafic and felsic magmatism was associated with the ca. 1380–1275 Ma Parnngurr Orogeny and further establishes correlations with the Mount West Orogeny in the Musgrave Province and “Stage 1” of the Albany-Fraser Orogeny. The new data support the progressive, final amalgamation of the Australian-Antarctic crustal fragments during the period ca. 1380–1250 Ma through consumption of oceanic crust below the over-riding West Australian Craton.

Perovskite U-Pb age and petrogenesis of the P-12 kimberlite from the Eastern Dharwar craton, southern India: Implications for a possible linkage to the 1110 Ma large igneous province

Petrology, bulk-rock geochemistry, and perovskite U-Pb age for the P-12 kimberlite pipe from the Wajrakarur kimberlite field, Eastern Dharwar craton (EDC) of southern India is reported. Perovskites yielded a high-precision U-Pb age of 1122 ± 7.7 Ma, taken to be an emplacement age of the host P-12 kimberlite pipe. The groundmass of coherent facies P-12 kimberlite contains monticellite, clinopyroxene, andradite, atoll spinel with titanomagnetite trend, and perovskite with an elevated REE contents. Phlogopite shows restricted Al2O3 and TiO2 contents. Furthermore, olivines with a wider and higher range of core compositions (i.e. Mg# = 84–94) and multi-granular nodules are the hallmark features of the P-12 pipe. This assorted primary mineral content and its composition indicates the transitional nature of the P-12 towards the Kaapvaal lamproites. However, concentrations of bulk-rock major and trace elements in the P-12 and other Wajrakarur kimberlites are similar to the global hypabyssal magmatic kimberlites. Large ion lithophile and high field strength elements (e.g. Ba and Nb) and their ratios (e.g. La/Nb and Th/Nb) suggest the presence of a heterogeneous and lithosphere influenced mantle source region which have been severely overprinted by metasomatizing fluids/melts emanating from the deep sourced upwelling mantle. The presence of such mixed and metasomatized mantle source regions likely to be an important factor for the transitional nature of the P-12 and other Mesoproterozoic kimberlites. Based on the availability of the newest emplacement ages, we propose a geodynamic model for the origin of kimberlites in the Indian subcontinent. The U-Pb age of 1122 ± 7.7 Ma for the P-12 pipe shows its close temporal association to the emplacement of the recently proposed 1110 Ma Large Igneous Province (LIP), with plume center beneath the NW part of the Kalahari craton. Emplacement of the P-12 and other contemporaneous Indian kimberlites, therefore, marks the impingement of mantle plume which contributed heat and triggered partial melting of metasomatized lithospheric mantle without melt input. The eruption phase of ~ 100 million years (i.e. 1050–1153 Ma), for the kimberlites and related rocks in the Indian shield, does not appear to be continuous and can be separated into several short-durational magmatic events. For this reason, small-volume, volatile-rich magmatism during the Mesoproterozoic time in India is linked to the presence of a number of LIPs and associated mantle plumes during Columbia to Rodinia supercontinent transition and assembly of cratonic blocks of the latter.

Re-Os geochronology highlights widespread latest Mesoproterozoic (ca. 1090–1050 Ma) cratonic basin development on northern Laurentia

Abstract The terminal Mesoproterozoic was a period of widespread tectonic convergence globally, culminating in the amalgamation of the Rodinia supercontinent. However, in Laurentia, long-lived orogenesis on its eastern margin was punctuated by short-lived extension that generated the Midcontinent Rift ca. 1110–1090 Ma. Whereas this cratonic rift basin is typically considered an isolated occurrence, a series of new depositional ages demonstrate that multiple cratonic basins in northern Laurentia originated around this time. We present a Re-Os isochron date of 1087.1 ± 5.9 Ma from organic-rich shales of the Agu Bay Formation of the Fury and Hecla Basin, which is one of four closely spaced cratonic basins spanning from northeastern Canada to northwestern Greenland known as the Bylot basins. This age is identical, within uncertainty, to ages from the Midcontinent Rift and the Amundsen Basin in northwestern Canada. These ages imply that the late Mesoproterozoic extensional episode in Laurentia was widespread and likely linked to a common origin. We propose that significant thermal anomalies and mantle upwelling related to supercontinent assembly centered around the Midcontinent Rift influenced the reactivation of crustal weaknesses in Arctic Laurentia beginning ca. 1090 Ma, triggering the formation of a series of cratonic basins.

Spatiotemporal Variations in Surface Heat Loss Imply a Heterogeneous Mantle Cooling History

AbstractEarth's heat budget is strongly influenced by spatial and temporal variations in surface heat flow caused by plate tectonic cycles. Here, we use a novel set of paleo‐seafloor age grids extending back to the mid‐Paleozoic to infer spatiotemporal variations in surface heat loss. The time‐averaged oceanic heat flow is 36.6 TW, or ∼25% greater than at present‐day. Our thermal budget for the mantle indicates that 149 K/Gyr of cooling occurred over this period, consistent with geochemical estimates of mantle cooling for the past 1 Gyr. Our analysis also suggests sustained rapid cooling of the Pacific mantle hemisphere, which may have cooled ∼50 K more than its African counterpart since 400 Ma. The extra heat released from the Pacific mantle may have been trapped there by the earlier long‐lived supercontinent Rodinia (∼1.1–0.7 Ga), and the Pacific mantle may still be hotter than the African mantle today.

North China craton: The conjugate margin for northwestern Laurentia in Rodinia

Abstract In the Rodinia supercontinent, Laurentia is placed at the center because it was flanked by late Neoproterozoic rifted margins; however, the conjugate margin for western Laurentia is still enigmatic. In this study, new paleomagnetic results have been obtained from 15 ca. 775 Ma mafic dikes in eastern Hebei Province, North China craton (NCC). Stepwise thermal demagnetization revealed a high-temperature component, directed northeast or southwest with shallow inclinations, with unblocking temperatures of as high as 580 °C. Rock magnetism suggests the component is carried by single-domain and pseudo-single-domain magnetite grains. Its primary origin is supported by a positive reversal test and regional remanence direction correlation test, and the paleomagnetic pole (29.0°S, 64.7°E, A95 = 5.4°) is not similar to any published younger poles of the NCC. Matching the late Mesoproterozoic to early Neoproterozoic (ca. 1110–775 Ma) apparent polar wander paths of the NCC and Laurentia suggests that the NCC could have been the conjugate margin for northwestern Laurentia in Rodinia, rather than sitting off the northeast coast of the main Rodinian landmass. Geological data indicate that breakup of the NCC and Laurentia occurred between ca. 775 and 720 Ma.

Neoproterozoic extension and decompression in the northern Eastern Ghats Province, India: Mid-crustal signature of Rodinia break-up?

The Eastern Ghats Province (EGP) of India is considered to have been a part of the supercontinents Rodinia and Gondwana at c. 1.0 Ga and 500 Ma, respectively. A range of ages spanning much of the Neoproterozoic have been periodically reported from parts of the EGP, indicating that the terrane remained tectonically active in the interval between Rodinia and Gondwana amalgamation, although the nature of the associated events remains uncertain. In this study conducted on the northern EGP, we constrain these enigmatic events from structural (field, microstructural and Electron Backscatter Diffraction studies), metamorphic (pseudosection modelling and geothermobarometry) and geochronological (monazite chemical dating) evidence. The area is multiply deformed, with the D1 and D2 shortening deformation accompanying granulite facies metamorphism that peaked at temperatures in excess of 900 °C, at ~955 ± 28 Ma. Following hydrous fluid infiltration at ~808 ± 10 Ma, the entire northern EGP was affected by an extensional deformation event D3 that reoriented all earlier fabrics into an E-W trending, northerly dipping orientation. Deformation microstructures and results of geothermobarometry indicate that D3 operated at around 600 °C at ~711 ± 18 Ma. Dextral strike-slip deformation (D4) along the Mahanadi Shear Zone operated under greenschist facies conditions and did not reset monazite isotope systematics in the region. The signature of mid-crustal extension during D3 is likely to be associated with the break-up of Rodinia. The lack of corresponding evidence for mid-Neoproterozoic extension in the adjacent Indian cratons suggests relative uplift of the EGP following Gondwana amalgamation.

Bimodal volcanic rocks in the northeastern margin of the Yangtze Block: Response to breakup of Rodinia supercontinent

Mid-Neoproterozoic protoliths of high–ultrahigh-pressure metamorphic rocks in the northeastern margin of the Yangtze Block preserve one of the best examples of 18O-depleted magmatic provinces worldwide, which is the significant record for lithospheric extension associated with continental rifting. In this contribution, we report the depleted 18O signature of felsic meta-volcanic rocks from the Zhangbaling Uplift (ZBLU), a segment of the Tan–Lu fault zone, which is located between the Dabie and Sulu orogenic belts. The low-δ18O signature of these rocks provides crucial information for understanding their origin and tectonic setting. Zircons yield UPb protolith ages of 771 ± 5 Ma to 761 ± 5 Ma and show a narrow range in δ18O values of 1.97‰ to 3.11‰. The typical syn-magmatic characteristics of these zircons indicate that they record inheritance from low-δ18O magmas during the mid-Neoproterozoic, which suggests the occurrence of high-temperature surface-water–rock interaction in a continental rift setting. Quartz keratophyres in the ZBLU exhibit A-type granite geochemical compositions with high contents of high-field-strength elements (Zr + Nb + Ce + Y > 350 ppm) and a zircon saturation temperature of 829 °C. The zircon grains have slightly depleted εHf(t) values of −3.4 to +1.9, which suggest Mesoproterozoic juvenile crustal formation in response to the amalgamation of the Yangtze Block with the Rodinia supercontinent. A few coeval spilites (758 Ma) crop out sporadically in the ZBLU. Their geochemical characteristics include high SiO2 contents (51.06–57.03 wt%), low Mg# values (42–53), and arc-like trace-element distribution patterns. The variable zircon εHf(t) values for the spilite samples can be divided into two groups: negative εHf(761 Ma) values of −16.4 to −11.1, and positive εHf(744 Ma) values of +5.9 to +8.5, which supports source mixing between enriched mantle and residual oceanic crustal material. In conclusion, the ZBLU spilite–keratophyre sequence is composed of a typical bimodal rock association, providing new petrological evidence for the origin of low-δ18O magmas and for a continental rift setting related to the separation of the Yangtze Block from the Rodinia supercontinent at ca. 771 Ma.

Neoproterozoic bimodal magmatism in the eastern Himalayan orogen: Tectonic implications for the Rodinia supercontinent evolution

Neoproterozoic magmatism associated with the assembly and configuration of the Rodinia supercontinent is widely distributed in the India-Himalayan terrane. However, its petrogenesis and tectonic settings remain controversial. This study provides new geochronological and geochemical data on the Neoproterozoic bimodal magmatism from the eastern Himalayan orogen. In situ zircon UPb dating revealed that the protoliths of amphibolites were emplaced at ca. 826 Ma and the granitic gneisses have crystallization ages of 825–820 Ma. The granitic gneisses exhibit geochemical features of A-type granites, with high initial (87Sr/86Sr)i ratio (0.7182–0.7394), low whole-rock εNd(t) (−8.4 to −6.6), and variable zircon εHf(t) (−7.4 to +1.0) values. They were probably generated by partial melting of the ancient lower crust with minor input of mantle components. The amphibolite samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), suggesting an arc affinity. They have relatively high initial (87Sr/86Sr)i ratios (0.7113–0.7136), low whole-rock εNd(t) (−1.1 to 1.4) and a wide range of zircon εHf(t) (−4.1 to 8.3) values, indicating that the protoliths of amphibolites were likely generated by partial melting of an enriched subduction-modified continental lithospheric mantle. Their geochemical signatures are similar to typical back-arc basin basalts. The presence of coeval A-type granites and arc-related mafic rocks is probably due to the existence of a back-arc system. We argue that the Neoproterozoic bimodal magmatism is a product of back-arc extension initiated at an early stage, resulting from the rollback of the Mozambique Oceanic slab. Combined with previous studies on Neoproterozoic magmas from India and the Himalayas, we suggest that an extensive Neoproterozoic back-arc system may have existed along the northwestern margin of the Rodinia supercontinent. This theory supports a scenario of an Andean-type continental margin for the India-Himalayan terrane during the middle Neoproterozoic.

West Africa in Rodinia: High quality paleomagnetic pole from the ~ 860 Ma Manso dyke swarm (Ghana)

The paleogeography of the Meso-Neoproterozoic Rodinia supercontinent remains debated partly because many stable cratons still lack reliable paleomagnetic data for this period. A new geochronological and paleomagnetic study was conducted on the NNW-trending Manso dyke swarm of southern West Africa (Ghana) to clarify the position of this unconstrained continent in Rodinia. Two UPb apatite ages of 857.2 ± 8.5 Ma and 855 ± 16 Ma agree with one previous baddeleyite age, indicating a ~ 860 Ma emplacement age for the Manso dykes. A characteristic remanent magnetization (ChRM) was isolated in stable single to pseudo-single domain (SD-PSD) magnetite. Well constrained site mean directions obtained for 13 dykes lead to a mean direction for the Manso dyke swarm of Dm = 181.9°, Im = −77.2° (N = 13, α95 = 7.6°, k = 30.6), yielding a paleomagnetic pole at 177.6°E, 28.3°S, (A95 = 12.7 °K = 11.6). Two directional clusters of opposite inclination pass a reversal test (C-class) and the primary origin is supported by a positive baked contact test, satisfying all the seven R-criteria to provide the first West African Tonian key paleomagnetic pole. This key pole indicates a high latitude for the West Africa Craton during the emplacement of the ~860 Manso dykes. A compilation of reliable paleomagnetic poles for West Africa, Baltica, Amazonia and Congo-São Francisco cratons suggests that these cratons were together between ~1200 and 800 Ma in a long-lived WABAMGO configuration. We suggest that the collision of this block with Laurentia along the Grenvillian-Sunsás orogens closed the external Nuna Ocean and formed Rodinia by extroversion.

Late Neoproterozoic – early Paleozoic basin evolution in the Coal Creek inlier of Yukon, Canada: implications for the tectonic evolution of northwestern Laurentia

The age and nature of the Neoproterozoic – early Paleozoic rift–drift transition has been interpreted differently along the length of the North American Cordillera. The Ediacaran “upper” group (herein elevated to the Rackla Group) of the Coal Creek inlier, Yukon, Canada, represents a key succession to reconstruct the sedimentation history of northwestern Laurentia across the Precambrian–Cambrian boundary and elucidate the timing of active tectonism during the protracted breakup of the supercontinent Rodinia. These previously undifferentiated late Neoproterozoic – early Paleozoic map units in the Coal Creek inlier are herein formally defined as the Lone, Cliff Creek, Mount Ina, Last Chance, Shade, and Shell Creek formations. New sedimentological and stratigraphic data from these units is used to reconstruct the depositional setting. In the Last Chance Formation, chemostratigraphic observations indicate a ca. 5‰ δ13Ccarbgradient coincident with the globally recognized ca. 574–567 Ma Shuram carbon isotope excursion. Map and stratigraphic relationships in the overlying Shell Creek Formation provide evidence for latest Ediacaran – middle Cambrian tilting and rift-related sedimentation. This provides evidence for active extension through the Cambrian Miaolingian Series in northwestern Canada, supporting arguments for a multiphase and protracted breakup of Rodinia.

Formation of the Neoproterozoic Continental Crust in the Structures of the Central Segment of the Central Asian Fold Belt

The paper considers the results of geochronological (U-Pb method, ID-TIMS), geochemical, and Sm-Nd isotopic studies of granitoids, volcanics, and terrigenous rocks of the eastern Dzabkhan terrane, as well as felsic volcanics of the Dzabkhan Formation in its southern part. It is established that the post-kinematic granitoids of the Dzabhan–Mandal Zone, Erdenekhairkhan, and Bogdoingol blocks were formed in the range of 813 ± 9–772 ± 3 and ca. 720 Ma, and the rhyolites of the Dzabkhan Formation were formed at 790 ± 3 Ma. The rock sources in the southern part of the terrane and in the Bogdoingol Block were mainly ancient crustal complexes. Nd isotopic data on the rocks of the Dzabkhan–Mandal Zone and the Erdenekhairkhan Block demonstrate the mixed nature of their sources and suggest a significant contribution of Early Neoproterozoic juvenile material. Based on obtained and previous data, it is shown that the Dzabkhan terrane is not a homogeneous block of the Early Precambrian continental crust, but represents a Neoproterozoic composite terrane consisting of rocks of island arc and continental margin complexes, and reworked Early Precambrian continental crust. The correlation of the Precambrian complexes of the Dzabkhan terrane with those of the Songino, Baidarik, and Tarbagatai terranes is discussed, and features of the formation of the Neoproterozoic continental crust in the central segment of the Central Asian fold belt are considered. It is established that the Khangay group terranes comprise widespread oceanic, island arc, continental margin, and riftogenic complexes formed at ca. 960–930, 880–850, and 810–790 Ma. Based on the data obtained, a model of the formation and evolution of the Neoproterozoic crust of the Central Asian fold belt is proposed by the example of paleoreconstructions for 925 and 825 Ma. It is assumed that the extensive growth of the Neoproterozoic continental crust of the region was related to the subduction processes in the framing of the Rodinia supercontinent at about 960–860 Ma ago and continental rifting that initiated the breakup of the supercontinent in the middle Tonian at about 860 and 800 Ma ago.

Precambrian obducted serpentinites in the Rhodope Massif

The Precambrian metamorphic complex in the Rhodope Massif is built of two lithostratigraphic units: the lower is an ancient granite-gneiss continental crust – Prarhodopian Group (PRG), and the upper one – a Neoproterozoic metamorphosed volcano-sedimentary rock complex – Rhodopian Group (RG). The lower stratigraphic levels of the RG are occupied by an ophiolitic association consisting of serpentinites, amphibolites, and metagabbros. The serpentinites constantly occupy the same level between the continental gneisses surface of the PRG and the base of the RG. The high degree of serpentinization (85–95%) indicates low temperature hydration metamorphism on the surface of an ultrabasic ocean plate. The formation of the Rhodope ophiolitic association has taken place in a Neoproterozoic supra-subduction zone in three stages: a. serpentinization at the ocean floor; b. obduction of serpentinite fragments, scraped from soft and plastic hydrated coat of the sliding ultrabasic plate; c. SSZ-type autochthonous Neoproterozoic (610–566 Ma) basic volcanism, including and covering serpentinite bodies. This determines a heterogeneous nature of the ophiolitic association. The lower granite-gneiss complex – PRG may have been a part of some microcontinent after the breaking of the supercontinent Rodinia. The formation of a supra-subduction zone – SSZ and the obduction of serpentinite fragments started during ocean closure preceding the amalgamation of supercontinent Gondwana.

Remnant of upper granulite continental crust in the Maurice Ewing Bank Complex (DSDP site 330, east Falkland-Malvinas Plateau) and role in Grenville orogeny

The Mesoproterozoic crust of remnant terranes such as Maurice Ewing Bank can provide crucial clues about Rodinia supercontinent. Petrological and geochemical studies were conducted to unravel the metamorphic history of the Maurice Ewing Bank Complex (MEBC). The MEBC is a polyphase metamorphic terrane with four progressive tectono-metamorphic events in subduction-related rocks. The first two episodes (R1-R2) occurred under conditions of progressive amphibolite- and granulite-facies metamorphism related to an orogenic hinterland. The R2 episode (P = 1.05 GPa, T = 800 °C) coincided with an older syn-deformational metagranitoid age of 1068 ± 28 Ma. The third episode (R3) involved granulite-facies metamorphism (P = 0.7–0.9 GPa, T = 830–930 °C) during tectonic exhumation that led to generation of syn- to late metagranitoids at 1032 ± 12 Ma. Episode four (R4) was marked by a regional anatectic process linked to crustal delamination at 1006 ± 13 Ma. Late retrograde metamorphic events, demonstrated by Rb-Sr and K-Ar isotopes, were generated by far-field thermal anomalies of Neoproterozoic-Palaeozoic tectonic events such as the Pan-African orogeny and Gondwanides. The correlation of the geotectonic environment and coeval magmatic-metamorphic events indicates that the MEBC comprises the roots of an orogenic hinterland of the Natal-Maurice-Maud belt during Rodinia-forming orogenies caused by the interaction of Kaapvaal and Patagonia cratons.

Nepheline syenite and related rocks at Meruda Takkar hill, northern Kachchh: Neoproterozoic Malani basement or Mesozoic alkaline magmatism?

An extremely small but significant exposure of possibly Precambrian or Pre-Deccan Mesozoic plutonic rocks spanning 200 × 90 m in size with 15 m elevation, remotely located amidst vast salt flats of the Great Rann of Kachchh received attention when it was first reported by Biswas in 1968; however, systematic petrological and petrographical studies remained undone. Therefore, in the present study, we addressed complete geological accounts to establish its possible origin. Our detailed geological study indicates that the complex is made up of nepheline and aegirine bearing alkali feldspar syenite with numerous fine-to-medium grained felsic dykes. It lays two viewpoints: (1) it has affinity with Trans Aravalli Belt anorogenic felsic magmatism, i.e., Precambrian and (2) it is genetically related to the pre-Deccan Mesozoic plutonic intrusives like Nir Wandh in Pachham Island and Mundwara and Sarnu–Dandali complexes in Rajasthan. The nearest felsic magmatic suite is an exposure of gray and pink granites of Nagar Parkar of Neoproterozoic age. Presence of undersaturated minerals and xenoliths of diorites within syenite parent body may suggest partial melting of lower crust probably during Rodinia supercontinent rifting. However, presence of alkali-rich minerals, alkali feldspars, kaersutite, aegirine, apatite and rutile needles and the complex being part of the Kachchh rift basin suggests its genetic resemblance with Pre-Deccan Mesozoic plutonic events. The radiometric age will confirm the age of this plutonic massif. Based on the field geological and petrographical studies of Meruda Takkar syenitic complex, two viewpoints have been raised: Radiometric age determination and geochemical analysis of the Meruda syenite are needed to establish its age and origin.

Identification of two-phased late Paleoproterozoic magmatism in the Wuyishan Domain (SE China): Implications for the tectonic evolution of the Cathaysia Block

The Cathaysia Block amalgamated with the Yangtze Block along the Jiangnan orogenic belt to form the South China Craton during early Neoproterozoic time. However, the origin of the Cathaysia Block and its position in the Nuna supercontinent remain controversial. This paper synthesizes geochronological, geochemical and isotopic data from late Paleoproterozoic igneous rocks in the Wuyishan Domain of the Cathaysia Block (SE China). Two-phases of late Paleoproterozoic A- and S-type granitoids were identified and dated at 1925–1848 Ma and 1816–1750 Ma. The A-type granites in the Wuyishan Domain were likely derived from partial melting of mafic lower crust with a tonalitic to granodioritic geochemical composition, and the S-type granites were derived from partial melting of a meta-sedimentary source. These late Paleoproterozoic granitoids were emplaced in a continental arc/back-arc setting and the two-phased arc/back-arc magmatism was related to the assembly of the Paleoproterozoic Nuna supercontinent. Combining our results with previous late Paleoproterozoic geochemical and age data, we suggest that the Cathaysia Block was located close to northern India Shield during Proterozoic time until the breakup of the Rodinia Supercontinent in the late Neoproterozoic.

Neoproterozoic magmatic and metamorphic imprints in the East Kunlun Orogenic Belt, North Tibetan Plateau, NW China: Implications for the assembly and initial breakup of the Rodinia supercontinent

The East Kunlun Orogenic Belt (EKOB), located on the northern margin of the Tibetan Plateau, experienced intense, long-lasting,and complicatedmulti-stage orogeny from the Neoproterozoic to Early Mesozoic. Neoproterozoic magmatic and metamorphic events recorded critical information on Precambrian tectonic evolutionary history. Zircon U-Pb ages of 914 ± 6.5, 902 ± 5.3, and 856 ± 6.8 Ma were determined for granitic gneiss, monzogranite, and charnockite, respectively. Geochemical and petrological studies reveal high SiO2, Al2O3, and K2O content with abundant Al-rich minerals, such as garnet and muscovite, which show typical S-type granite properties. The εHf(t) values ranging from − 6.5 to + 5.6 (TDM2 = 1.4–2.2 Ga) indicate a primarily Paleoproterozoic metagreywackes and metapelitic derivation with mantle contribution. Zircon U-Pb results show that amphibolite yielded ages of 846 ± 5.2 Ma. Geochemistry andεHf(t) values ranging from 10.5 to 15.9 (TDM1 = 0.8–0.9 Ga) suggest that the mafic magma originated from depleted mantle metasomatized by subduction fluid. We propose that the Neoproterozoic rocks in this study were generated in syn-orogenesis and incipient continental rift-related extension environment, whichcorresponds to the assembly and initial breakup of the Rodinia supercontinent. In the EKOB, The initial breakup-related extension of the supercontinent affected by super plume occurred at ca. ~ 0.85 Ga. East Kunlun and its adjacent blocks were within a single tectonic domain and recorded important evolutionary history of the Rodinia supercontinent.