Breakup Of Rodinia Research Articles

Caledonian reactivation and reworking of Timanian thrust systems and implications for latest Mesoproterozoic to mid-Paleozoic tectonics and magmatism in northern Baltica

Background The Trollfjorden–Komagelva Fault Zone is the southernmost thrust fault of the Timanian Orogen and extends for thousands of kilometers from northwestern Russia to northern Norway. Though there is little about its location onshore northeastern Norway, where it is mapped as a major fault system dominantly comprised of NNE-dipping thrust faults, its continuation to the west below Caledonian nappes and offshore post-Caledonian sedimentary basins remains a matter of debate. Methods The present study provides a more definitive answer about the continuation of Trollfjorden–Komagelva Fault Zone west of the Varanger Peninsula by using seismic reflection, bathymetric, topographic, and magnetic data onshore Finnmark and offshore on the Finnmark Platform. Results The present study demonstrates that the Sørøya–Ingøya shear zone represents a portion of the Trollfjorden–Komagelva Fault Zone that was folded into a NE–SW orientation and reactivated as a top-southeast thrust during the Caledonian Orogeny, while other portions of the Trollfjorden–Komagelva Fault Zone (e.g., on the Varanger Peninsula) were reactivated as strike-slip faults. The study also documents the presence of another major, NNE-dipping Timanian shear zone with a similar geometry to the Trollfjorden–Komagelva Fault Zone north of the Varanger Peninsula. Conclusions The Trollfjorden–Komagelva Fault Zone may continue offshore as a NE–SW-striking folded structure. This has the following implications: (1) the Seiland Igneous Province likely formed in a backarc setting, (2) metasedimentary rocks of the Kalak Nappe Complex deposited along the Baltican margin of the Iapetus Ocean, possibly in a late–post-Grenvillian collapse basin, (3) the Iapetus Ocean was much narrower than the several thousands of kilometers width commonly proposed, and (4) early Neoproterozoic magmatism in northern Norway is possibly related to the initial breakup of Rodinia.

Two phases of granulite-facies metamorphism superimposied on retrograde eclogite: Constraints on the early Paleozoic tectonic evolution of the Qinling Orogenic Belt, central China

Existing studies provide adequate petrological evidences on ca. 500 Ma ultra-high pressure (UHP) metamorphism in the North Qinling Orogenic Belt (NQOB) in central China, but the genesis of 470–420 Ma multi-phase granulite-facies metamorphism in the NQOB and their relationship with the ca. 500 Ma UHP metamorphism remain controversial, resulting in the early Paleozoic evolution of the Qinling Orogenic Belt (QOB) highly debatable. In this study, we present mafic granulites and host felsic gneisses with a “red-eye socket” texture from the Shuanglong area, eastern NQOB, which recorded two phases of granulite-facies metamorphism superimposing on former eclogite-facies metamorphism. The former eclogite-facies metamorphism is indicated by eclogite-facies zircon trace element patterns and 496–495 Ma zircon ages, which are the same with those of the HP–UHP eclogite-facies metamorphic rocks in NQOB. The first granulite-facies metamorphism occurred at 460–448 Ma is characterized by coarse-grained minerals in matrix. Compositions and zonings of these minerals define an anticlockwise P–T path involving a prograde stage (751–763 °C), a high-temperature peak stage (9.2 kbar and 864 °C), and a near-isobaric cooling retrograde stage (8.3 kbar and 818 °C). The second granulite-facies metamorphism occurred at 422–421 Ma is represented by coronal garnet and coexisting fine-grained mineral aggregates. Coronal garnet compositional zonings suggest a clockwise P–T path consisting of a high-pressure peak stage (9.5–11.2 kbar and 748–783 °C) and a decompressing and heating retrograde stage (9.2–9.5 kbar and 789–800 °C). Combining dating results of leucosomes in these rocks and existing data, we proposed a new model for early Paleozoic tectonic evolution of the NQOB. The North Qinling Terrane (NQT), probably separated from the South China Block (SCB) during the breakup of Rodinia, drifted northwards and underwent UHP metamorphism at 500 Ma and then rapidly exhumed to crust level. Later, the Shangdan Ocean subducted northwards beneath the exhumed NQT at 470–440 Ma, resulting in the first granulite-facies metamorphism and contemporaneous migmatization and magmatism. Finally, the closure of the Shangdan Ocean led to collision between the NQT and South Qinling Terrane/SCB and the second granulite-facies metamorphism and anatexis at 422–418 Ma.

Diverse magmatism along the northern margin of Tarim during the Ediacaran: Transition from Rodinian dispersing to Gondwana assemblage

The Ediacaran igneous rocks and sedimentary sequences play a key role for our understanding the transition from dispersing of the Rodinian continents to the assemblage of the Gondwana. On the other hand, some continental massifs at the marginal area of the Rodinia and Gondwana could preserve solid evidences for deciphering the geodynamic background from the break-up of Rodinia to the assemblage of Gondwana. In this contribution, we report field observations, petrography, ages and systematic geochemistry of the diverse Ediacaran igneous activities in the northern margin of the Tarim Block, which was favored as a marginal continental massif in the Rodinia configuration by most geologists. The Ediacaran igneous rocks along the northern margin of Tarim include the Baicheng and Yangxia granites, Tiemenguan syenite, Kurle mafic dykes and the basalt layers in the Zamoketi Formation (northeastern Tarim) and the Sugetbrak Formation (northwestern Tarim). Precise zircon UPb dating revealed that these distinct rocks were broadly coeval with crystallization/eruption ages of 630–600 Ma. Bulk-rock elemental and SrNd isotope compositions as well as zircon LuHf isotope compositions demonstrate that the Baicheng and Yangxia granites were derived from Neoarchean mafic lower crust and underwent intensive fractionation before their emplacements. The Tiemenguan syenites have potassic andesitic compositions, in combination with their pronounced enriched NdHf isotopes and extremely high Zr saturation temperatures (∼900 °C), we argue that their possible shoshonitic primary magmas were derived from previously metasomatized subcontinental lithospheric mantle source (amphibole-bearing) and then, coupling with assimilation and fractional crystallization (AFC) effects in magma chamber and/or en route to the emplacement space. This can account for their intriguing geochemical features. The ca. 615 Ma Zamoketi and Sugetbrak basalts and the slightly younger porphyrite dykes (ca. 580 Ma) cutting the Zamoketi basalt layer, show typical OIB-like geochemical signatures, they were most likely derived from a depleted asthenospheric mantle source with variable fractionation of olivine and pyroxene and negligible crustal contamination before eruption. On the whole, the geochemistry of the diverse Ediacaran igneous rocks unambiguously demonstrates that they were genetically related to an extensional environment. In combination with the significant passive continental features of the Ediacaran-Cambrian sedimentary sequences, we consider that these Ediacaran igneous rocks were the latest phase of igneous activity related to the dispersing of the Tarim at the margin of the Rodinia supercontinent.The dispersing of the Rodinian supra-continent was diachronic with the assemblage of the Gondwana. Late Tonian to Ediacaran dispersing of the Tarim from northern margin of Australia induced the opening of the Proto-Tethys Ocean. Then the initiation of the southward subduction of the Proto-Tethys Ocean at ca. 530 Ma (Fortunian) led to the Tarim assemblage to Gondwana at ca. 440 Ma.

The Early Neoproterozoic Andean-Type Orogenic and Within-Plate Magmatic Events in the Northern Margin of the Yangtze Craton during the Convergence of the Rodinia Supercontinent

Although considered a crucial component of the Rodinia supercontinent, it remains uncertain how the Yangtze craton relates to the accretion and breakup of Rodinia. Here, the Huanglingmiao granitic complex (HGC), an intermediate-acid rock series that intruded on the southern Kongling terrane of the northern Yangtze craton margin, is investigated to help resolve this conundrum. Our analysis indicates that these rocks consist of tonalite, trondhjemite, granodiorite, oligoporphyritic granodiorite, porphyric biotite granodiorite, and fine- to medium-grained granodiorite dyke compositions. Collectively, this assemblage is further subdivided into two categories by their temporal, spatial, and geochemical features into early TTG-like and later granitic–dioritic units, which are composed of tonalite, trondhjemite, granodiorite, porphyritic granodiorite, and the fine- to medium-grained granodiorite dykes, respectively. Zircon U-Pb dating yields ages of 865~850 Ma for the TTG-like rocks, 844~825 Ma for the porphyritic granodiorites, and ~800 Ma for the granodiorite dykes. Combined with geochemical evidence, the data suggest that the early- and late-series rocks were formed by a partial melting of Mesoproterozoic and Paleoproterozoic crustal materials, respectively, suggesting that the vertical layering of the crust controlled the composition of the independent units. In addition, isotopic evidence points to different sources for the various rocks in the Kongling terrane and that mantle-derived materials influenced the early-series lithologies. Combined with previous studies on the northern margin of the Yangtze craton, it is inferred that the early-series rocks formed in an active continental margin environment, while the late-series rocks display within-plate boundary formation characteristics. The multiple magmatic activities revealed by this study record sequential partial melting with tectonic transition characteristics from an Andean-type to within-plate magmatism in the northern margin of the Yangtze craton. Taken together, these observations point to a strong association between these rocks, convergence, and incorporation of the northern Yangtze craton margin into the Rodinia supercontinent during the Tonian Period.

Magmatic and sedimentological arguments for an Ediacaran active margin in the Bayankhongor Zone in western Mongolia, Central Asian Orogenic Belt

Geochronological and geochemical investigation of the magmatic and sedimentary rocks from the south-eastern tip of the Bayankhongor Zone (central Mongolia) constrains the Neoproterozoic evolution of the northern margin of the Baidrag Block. There, ultramafic to felsic igneous rocks of the Khan-Uul Massif intruded the volcano-sedimentary sequence of the Ulziit Gol Unit. U–Pb zircon ages show that both the plutonic and volcanic rocks were coeval products of the same Ediacaran (598–564 Ma) magmatism. Most of the samples have low contents of high field strength elements typical of arc-related magmas; however, some mafic rock samples display N-MORB-like chemistry. Magmatic rocks in the Khan-Uul Massif and Ulziit Gol Unit yielded exclusively positive initial εHf in zircon values (+4.9 to +13.8), implying derivation from depleted-mantle sources. Furthermore, heterogeneity of the whole-rock initial εNd values (–4.0 to +2.1) documents that fractional crystallization was accompanied by variable crustal contamination. The detrital zircon age patterns of the sandstone and tuffites in the Ulziit Gol Unit indicate that the sequence was filled dominantly by Ediacaran magmatic detritus derived from the Khan-Uul Massif and its volcanic equivalents, while the older cratonic material from the Baidrag basement represented only a subordinate component. Combined magmatic and sedimentary records imply that both the Khan-Uul Massif and the Ulziit Gol Unit may have formed in the same back-arc basin environment. This challenges the previous view that the entire Bayankhongor Zone was ophiolitic in nature. Distribution of coeval Ediacaran supra-subduction systems on the scale of the Mongolian Collage indicates the closure of multiple oceanic basins rimming the Siberian Continent. Following Rodinia break-up, this peri-Siberian realm was presumably formed by sub-parallel continental ribbons and oceanic basins. It is proposed that the amalgamation of these blocks and closure of intervening oceans reflected the Ediacaran advancing mode of the Palaeo-Pacific subduction.

Early-stage intracontinental rifting in the Neoproterozoic Centralian Superbasin: Systematic U–Pb and Lu–Hf isotopes in detrital and inherited zircons from the Yeneena Basin, northwest Australia

Detrital zircons from different lithostratigraphic units of Supersequence 1 across the Neoproterozoic northwest Officer and Yeneena basins were investigated using LA-ICPMS U−Pb and Lu − Hf isotope analyses to understand the source of detritus and potential links to regional tectono-magmatic events, as well as the crustal evolution of the sedimentary sources terranes. All data show that Proterozoic detritus dominate the age spectra of samples from the Yeneena Basin and northwest Officer Basin, with signatures varying in the heights of peaks rather than the presence or absence of age groups in different formations. The Archean and Proterozoic ages overlap with known magmatic events in the Pilbara Craton, Fortescue Basin, Rudall Province, Capricorn Orogen, Musgrave Province, Madura Province, and the Coompana Province suggesting these terranes are possible sources of the detritus. The detrital zircon population of the samples have main age peaks in the range 1300 to 1000 Ma, suggesting magmatic rocks of the Rudall and Musgrave provinces are the main sources of detrital zircons, which can be differentiated by Hf signature. The distal Musgrave Province persistently dominates the provenance of detritus in the northwestern Officer and Yeneena basins, while detritus from the proximal Rudall Province contributes to a lesser extent. This suggests that the distal Musgrave Province remained emergent during the evolution of the northwestern Officer Basin and the Yeneena Basin, whereas the proximal Rudall Province potentially became buried by the accumulating sedimentary rocks and contributed less detrital zircons. The 833.6 ± 1.4 Ma maximum depositional age obtained in this study for the sedimentary rocks of the northwestern Officer and Yeneena basins point to the approximate time of the start of basins development. The extensional event in this age period is related to emplacement and extrusion of the ca. 830 Ma Willouran Large Igneous Province (LIP). The Duke gabbro sills observed in the Yeneena Basin are part of this LIP, which extends from the Adelaide Rift Complex, through the Musgrave Province, central–northwest Officer Basin and into the Yeneena Basin. The sediment source terranes suggest a southeast–northwest oriented depositional system between central and Western Australia, possibly because of intracontinental rifting related to widespread mafic–ultramafic magmatic events that could include the earlier Ngaanyatjarra Rift formed by the 1090–1040 Ma Warakurna LIP as well as the ca. 830 Ma Willouran LIP, synchronous with the breakup of Rodinia in the mid-Neoproterozoic.

Neoproterozoic tectonic shift along the western margin of the Yangtze block, South China craton: Implications for its paleogeographic position during the Rodinia−Gondwana transition

Neoproterozoic igneous rocks in the Panxi region from the western margin of the Yangtze block, South China craton, record major changes in tectonic evolution and crustal thickness, and provide important constraints on the paleogeographic position and climate changes of the block in Rodinia and Gondwana reconstructions. Our new dating results show that the Pengguan complex from the Panxi region comprises ca. 743 Ma adakitic granodiorites and ca. 741 Ma A-type granites. The former is plagioclase-rich and has relatively low SiO2 content (65.22−67.36 wt%), high Mg# values (44.40−52.33), Sr/Y (23.22−61.94) and (La/Yb)N ratios (normalized to chondritic values; 13.41−24.00), with positive whole-rock εNd(t) values (+1.17 to +5.15), and high zircon εHf(t) (+5.53 to +8.83) and low zircon δ18O (4.21‰ to 5.51‰) values, indicating derivation from the partial melting of thickened juvenile mafic lower crust. By contrast, the granites are rich in K-feldspar and have high SiO2 contents (78.71−84.62 wt%), 10,000 × Ga/Al ratios (>2.6), and Fe/Mg ratios, with negative εNd(t) values (−1.47 to −0.02), high zircon εHf(t) (+2.94 to +9.77), and high saturation temperatures (828−920 °C). These features indicate fractional crystallization and partial melting of continental crust in a low-pressure, high-temperature, extensional environment. Integrated with the zircon Eu anomalies (Eu/Eu*) data and Hf-O isotopic data on pre-740 Ma magmatism in the Panxi region, we find that a rapid increase of crustal thickening (820−740 Ma) was synchronous with a gradual decrease of zircon δ18O and an increase of zircon εHf(t) values. These variations indicate an increase in the degree of hybridization between mantle sources and subducting slab-derived materials, thus generating a great number of low-δ18O melts, and continuous crustal thickening through the underplating of juvenile magmas. In addition, thinning of the crust since ca. 740 Ma, along with the gradual increase in zircon δ18O and εHf(t), suggests a shift from regional compression to extension. This documented shift, together with regional data from along the western margin of the Yangtze block, indicates a change from the well-developed and long-established Panxi convergent plate margin arc system (at least ca. 870−750 Ma) to passive-margin development and Cryogenian (720−635 Ma) glaciation. The long-lived subduction zone requires a peripheral location of South China that was linked to northern India during the Rodinia breakup. The subsequent and contemporaneous passive-margin development of the Yangtze block and India, along with the similar tectonic affinities of the Cathaysia block with India, indicate that South China lay outboard of the northern Gondwana margin during the assembly of this supercontinent.

Evolution of Neoproterozoic siliciclastic Kerur Formation in the light of sequence stratigraphic framework: Badami Basin, Karnataka, India

Field-based sedimentology, state of the art facies analysis and sequence stratigraphic framework analysis have revealed the controls of local and global tectonics, basin-marginal slope, climate and changes in relative sea level (RSL) over the sedimentation pattern and evolution of a Neoproterozoic Kerur Formation within the Badami Group of Kaladgi Supergroup in India. The entire succession shows three major cycles of deposition. Facies study and fluvial architectural elemental analysis suggest considerable variations in depositional environments as well as palaeogeography. A transition from basin-margin alluvial cone deposits to braided system, initially with fluctuating ephemeral flows then to a steadier semi-perennial nature, is discernible within the 1st cycle, in response to decreasing depositional slope with rising water table. The initial alluvial cone and braided ephemeral streams of high slope areas is designated as a product of low accommodation systems tract (LAST), while the semi-perennial system with steadier flows, representing the axial river of the initial rift valley, appears to be a product of high – accommodation systems tract (HAST). The 2nd cycle begins with a perennial and steady braided river system and grades upward to a shallow marine succession, comprising wave-dominated, well-sorted sandstone, with a granular transgressive lag at the base. Thus, the bottommost fluvial interval of the 2nd cycle constitutes the lowstand systems tract (LST). The marine succession represents deposits of outer shelf offshore to foreshore-beach settings and is composed of an initially deepening and fining upward transgressive systems tract (TST), followed by a coarsening and shallowing upward highstand systems tract (HST) with a maximum marine flooding surface (MFS) in between, demarcated by a shale-rich condensed zone. The 3rd cycle, with its prograding alluvial fan and aggrading braided fluvial deposits and restricted occurrence, represents only the low accommodation systems tract (LAST) with a subaerial unconformity at the base. The basin evidently initiated in the western sector, followed by its eastward expansion during the first major rejuvenation of the basin margin faults, after the deposition of the 1st cycle. After the basin-wide deposition of the 2nd cycle, restricted development of the 3rd cycle took place in the western sector only, following the second major rejuvenation of the fault system. The proposed sedimentological model, supported by established geochronological constraints, suggests that the sedimentation in the 1st cycle begins with scree cones, alluvial fans and braided ephemeral channel networks, originated from faulted basin margins within a riftogenic setting possibly related to the global-scale extensional tectonics of Rodinia breakup. After the expansion of the basin, the marine inundation has been correlated to the transgression that possibly took place during the post-rift maturation stages.

Evolution and extinction in a supercontinental world: did the breakup of Rodinia provide metazoans with evolutionary salvation?

A time discrepancy of at least 200–300 million years exists between the generally accepted onset of metazoan evolution as currently evidenced from fossils compared with that from studies at the molecular level. That temporal disparity coincides with the existence and subsequent breakup of the Rodinia Supercontinent when the earliest evolutionary crucibles were isolated intracratonic basins rather than the globally connected shallow seaways of subsequent eras. However, the discovery of fossil evidence to complement the extrapolations from molecular data has been, and continues to be, hampered, by both the geographical limitations of these isolated intracratonic basins and the fact that any such discovery would conflict with the global geological mindset that macrofossils of such age do not exist. Yet recently identified within the intracratonic Amadeus Basin of central Australia is a suite of macroscopic metazoan fossils that dates to ca 850–840 Ma, exemplifying an early attempt at animal evolution within the restrictions of the Rodinia Supercontinent. Such early metazoan evolution within such isolated crucibles, however, was extremely vulnerable to variations in climatic conditions, which threatened total extinction because the isolation of these basins limited metazoan distribution by denying them the possibility of migrating to safer havens. The Amadeus Basin evidence suggests that early metazoan evolution perhaps comprised cycles of about 10 million years when evolution flourished followed by climate change induced extinction and a subsequent evolutionary void of between 50 and 100 million years. Such cycles possibly characterised metazoan evolution until the Rodinia Supercontinent broke-up, after which connections between smaller oceans, shallow seas and narrow waterways provided metazoan life passageway to sanctuary during times of environmental stress. As the Amadeus Basin was just one of a number of isolated Rodinian-aged intracratonic basins, it is likely that similar fossils of the earliest metazoans are preserved elsewhere awaiting discovery.

Subduction retreating caused the external breakup of Rodinia: Constraints from the Neoproterozoic igneous rocks in the western Yangtze Block, South China

The western Yangtze Block is an ideal place for investigating the Precambrian tectonic evolution of the South China Craton and the geodynamic mechanism responsible for the breakup of Rodinia. However, the Neoproterozoic tectonic evolution of the western Yangtze Block has not been fully elucidated; in particular, the driving mechanism has changed from an arc setting to a rift setting. Here, we present new zircon U–Pb geochronology and O–Hf isotopic compositions, whole-rock geochemistry, and Sr–Nd isotope data for Yanbian andesites and Shimian gabbros from the western Yangtze Block, South China. The ca. 850–840 Ma Yanbian andesites are high-Mg andesites with moderate SiO2 (56.75–60.21 wt%) and high MgO (4.24–6.44 wt%) and Mg# (52–66). These rocks show enrichments in large-ion lithophile elements (LILEs; e.g., Rb, Ba, Sr, and K) and light rare earth elements (LREEs) and depletions in high-field strength elements (HFSEs; e.g., Nb, Ta and Ti) and display decoupled Nd–Hf isotopes (εNd(t) = +3.9 to + 5.0, εHf(t) = +9.7 to + 13.1) and relatively high zircon δ18O values (5.82–7.72 ‰); these findings indicate that these rocks were derived from a mantle wedge enriched by slab fluids and sediment melts. The ca. 820–810 Ma Shimian calc-alkaline gabbros are characterized by enriched LREEs and LILEs (e.g., Rb, Sr, and K) and depleted HFSEs (e.g., Nb, Ta and Ti). These rocks show decoupled Nd–Hf isotopes (εNd(t) = +3.2 to + 4.2, εHf(t) = +3.1 to + 7.5) and relatively low zircon δ18O values (4.28–5.31 ‰), indicating that they were formed by partial melting of mantle wedge metasomatized by sediment and oceanic slab melts. Compiled geochronological data suggest that Neoproterozoic subduction-related magmatism along the western Yangtze Block formed a long-term active arc system. Slab retreat in this subduction zone led to a shift in the tectonic setting from a compressional setting to an extensional setting in the Yangtze Block during the middle to late Neoproterozoic. Moreover, the temporal link between retreating subduction zone and extensional tectonics in the Yangtze Block suggests that protracted subduction retreating resulted in external rifting in Rodinia.

Geologic fingerprints of the Rodinia breakup in the western North China Craton: Constraints from the Early Neoproterozoic (ca. 825–810 Ma) mafic volcanic and intrusive rocks in the Langshan tectonic belt

As an important component of the East Asian continental block, the North China Craton (NCC) is crucial for reconstructing Rodinia in the Neoproterozoic. However, whether the NCC is a component of the Rodinia supercontinent and records its breakup remains enigmatic. Here, we identified Langshan gabbro and mafic dikes with ages of ca. 829–826 Ma and mafic volcanic rocks with ages of 810 ± 3 Ma in the northeastern Alxa Block of the western NCC. The Langshan gabbro shows flat rare earth element (REE) patterns [(La/Yb)N = 1.3–1.5] and slight enrichment in most incompatible trace elements, similar to enriched mid-ocean ridge basalt. The mafic volcanic rocks show the geochemical features of oceanic island basalt, including high total alkaline content (7.86–8.47 wt%), enriched in light REEs (La/YbN = 8.0–9.1), and insignificant Eu anomalies. Together with contemporaneous felsic volcanic rocks identified in previous studies, the mafic volcanic rocks (ca. 810 Ma) define a bimodal association. The mafic intrusive and associated dike swarms from ca. 825–810 Ma along with the coeval Jinchuan ultramafic–mafic intrusions, followed by rifting sedimentary successions, were formed in an extensional rift setting, supporting the geologic fingerprints of the Rodinia breakup in the western NCC. The well-matched mafic magmatic barcodes, similar provenance, and sedimentary successions preserved in the Adelaide superbasin of southeastern Australia and the Langshan rift basin of the western NCC support a possible link between the NCC and Australia during the Early Neoproterozoic.

Neoproterozoic low-T/P metamorphism in the Yangtze Block manifests a long-lived subduction girdle around Rodinia

Identifying long-lived subduction at the periphery of supercontinents provides insights into the processes of block assembly and dispersal within the supercontinent cycle. The Yangtze Block of South China stands as a key component during the transition from Rodinia to Gondwana, characterized by active tectono-magmatic processes throughout the early to middle Neoproterozoic. However, the lack of metamorphic records associated with accretionary orogenesis results in ambiguity about the tectonic regime and its evolution in Rodinia during this period. Here, we present evidence of low-temperature/pressure ratio (low-T/P) metamorphism in phengite-bearing orthogneisses from the western margin of the Yangtze Block (WYB). Through petrographic investigations and zircon U–Pb–Hf–O isotopic analysis in core and rim domains, we identify two distinct metamorphic rock types, with protolith ages of 1419 ± 19 Ma and 831 ± 9 Ma. Both rock types record metamorphism at ca. 830–820 Ma, accompanied by infiltration of externally-derived melts with high-δ18O and unradiogenic Hf isotopes. Our phase equilibria modeling, combined with mineral thermometry and Si-in-phengite content, shows peak metamorphic conditions of ∼550 °C and ∼8.2–8.6 kbar, corresponding to a cold geothermal gradient (19.0–20.5 °C/km). The low-T/P metamorphism is interpreted to occur either in a subduction zone accretionary wedge or in an overriding forearc continental crust, providing robust evidence for Neoproterozoic orogenesis of the WYB within a subduction framework. Based on petrological, isotopic, and paleomagnetic data, we conclude that the WYB represents part of a long-lived subduction girdle (at least ca. 970–750 Ma) at the periphery of Rodinia. Since the early stage of Rodinia breakup, this girdle was involved in alternating advance and retreat accretionary orogenesis as the Yangtze Block continuously drifted away from a mantle upwelling toward the degree-2 girdle of mantle downwelling. Our study provides a snapshot of the evolution of a complete long-lived circum-Rodinian subduction girdle during the transition from Rodinia to Gondwana.

Petrogenesis and tectonic implications of the Bloubergstrand basaltic andesites, Tygerberg Formation, Malmesbury Group, Pan-African Saldania Belt, southwestern Africa

Abstract The Bloubergstrand Member, consisting of mafic to intermediate tuffs and flows within the Tygerberg Formation of the Malmesbury Group, is a crucial but understudied component of the western Saldania Belt in southwestern Africa. With a U-Pb zircon age of 555 ± 5 Ma, these volcanic rocks provide valuable insights into the origins and, more broadly, the tectonic setting of the Saldania Belt during the final stages of Malmesbury Group sedimentation in the context of the construction of southwestern Gondwana at approximately 560 to 540 Ma. The Bloubergstrand Member amygdaloidal volcanic rocks vary from basaltic andesitic to andesitic and have experienced varying degrees of alteration. The volcanic rocks are enriched in the large ion lithophile elements (LILE) relative to the high field strength elements (HFSE). When normalised to primitive mantle values, they show enrichment in Cs, Rb, K and Pb and mild enrichment in Th, U, Zr and Hf, with the light rare earth elements (LREE) enriched relative to the heavy rare earth elements (HREE). They are depleted in Ba, Nb, Ta, Sr, Eu, P and Ti. εNd(t) values are mildly negative ranging from -3.60 to -2.39, and Nd TDM model ages range from 1.4 to 1.7 Ga. Initial 87Sr/86Sr ratios vary from 0.70478 to 0.70620, with one higher value of 0.72270, the latter likely due to extensive alteration. The Bloubergstrand Member volcanic rocks exhibit characteristics suggesting their origin from partial melting of lithospheric to transitional asthenospheric upper mantle, influenced by sediment-derived melts and variable degrees of crustal contamination. With continental arc basalt compositions and similarities to shoshonites, the samples reflect variable degrees of partial melting and source heterogeneities. Fractional crystallisation of pyroxenes, hornblende, and plagioclase contributes to compositional variability. Erupting in a continental arc margin, likely part of the Arachania block of the Kalahari craton, separated during the Tonian break-up of Rodinia, the volcanics were associated with the Marmora basin formed by eastward-directed subduction below the western Kaapvaal Craton margin. Extruded in a distal position relative to the Cuchilla Dionisio Arc in present-day southern Brazil and Uruguay, these volcanic rocks preceded the closure of the southern Marmora basin. The mantle melting, possibly a result of slab roll-back, break-off, ridge subduction, or a combination, served as a precursor to the lower crustal heating that generated the granitic magmas of the Cape Granite Suite.

Caledonian reactivation and reworking of Timanian thrust systems and implications for latest Mesoproterozoic to mid-Paleozoic tectonics and magmatism in northern Baltica

Background The Trollfjorden–Komagelva Fault Zone is the southernmost thrust fault of the Timanian Orogen and extends for thousands of kilometers from northwestern Russia to northern Norway. Though there is little about its location onshore northeastern Norway, where it is mapped as a major fault system dominantly comprised of NNE-dipping thrust faults, its continuation to the west below Caledonian nappes and offshore post-Caledonian sedimentary basins remains a matter of debate. Methods The present study provides a more definitive answer about the continuation of Trollfjorden–Komagelva Fault Zone west of the Varanger Peninsula by using seismic reflection, bathymetric, topographic, and magnetic data onshore Finnmark and offshore on the Finnmark Platform. Results The NNE-dipping Trollfjorden–Komagelva Fault Zone merges with a recently identified northwest-dipping brittle–ductile thrust, the Sørøya–Ingøya shear zone, which was previously thought to have formed during the Caledonian Orogeny. The present study demonstrates that the Sørøya–Ingøya shear zone represents a portion of the Trollfjorden–Komagelva Fault Zone that was folded into a NE–SW orientation and reactivated as a top-southeast thrust during the Caledonian Orogeny, while other portions of the Trollfjorden–Komagelva Fault Zone (e.g., on the Varanger Peninsula) were reactivated as strike-slip faults. The study also documents the presence of another major, NNE-dipping Timanian shear zone with a similar geometry to the Trollfjorden–Komagelva Fault Zone north of the Varanger Peninsula. Conclusions The present study suggests that (1) the Seiland Igneous Province formed in a backarc setting, (2) metasedimentary rocks of the Kalak Nappe Complex deposited along the Baltican margin of the Iapetus Ocean, possibly in a late–post-Grenvillian collapse basin, (3) the Iapetus Ocean was much narrower than the several thousands of kilometers width commonly proposed, and (4) early Neoproterozoic magmatism in northern Norway is related to the initial breakup of Rodinia.

Duration of Sturtian “Snowball Earth” glaciation linked to exceptionally low mid-ocean ridge outgassing

Abstract The Sturtian “Snowball Earth” glaciation (ca. 717–661 Ma) is regarded as the most extreme interval of icehouse climate in Earth’s history. The exact trigger and sustention mechanisms for this long-lived global glaciation remain obscure. The most widely debated causes are silicate weathering of the ca. 718 Ma Franklin large igneous province (LIP) and changes in the length and degassing of continental arcs. A new generation of two independent Neoproterozoic full-plate tectonic models now allows us to quantify the role of tectonics in initiating and sustaining the Sturtian glaciation. We find that continental arc length remains relatively constant from 850 Ma until the end of the glaciation in both models and is unlikely to play a role. The two plate motion models diverge in their predictions of the timing and progression of Rodinia break-up, ocean-basin age, ocean-basement depth, sea-level evolution, and mid-ocean ridge (MOR) carbon outflux. One model predicts MOR outflux and ocean basin volume–driven sea level lower than during the Late Cenozoic glaciation, while the other predicts outgassing and sea level exceeding those of the Late Cretaceous hothouse climate. The second model would preclude a major glaciation, while the first model implies that the trigger for the Sturtian glaciation could have been a combination of an extremely low MOR outflux (~9 Mt C/yr) and Franklin LIP weathering. Such minimal outflux could have maintained an icehouse state for 57 m.y. when silicate weathering was markedly reduced, with a gradual build-up of MOR CO2 in the atmosphere paired with terrestrial volcanism leading to its termination.

The origin and tectonic evolution of the late Neoproterozoic rift basin in the Tarim Craton, NW China

The Cryogenian-early Paleozoic succession in the Tarim Craton is generally regarded as a continuous rift sequence that followed the prolonged superplume-related breakup of Rodinia. However, the rift architecture and origin of the late Neoproterozoic basin are poorly known, but these are important for the understanding of the tectonic evolution of the basin and for the evaluation of the hydrocarbon potential. This paper aims to elucidate the rift architecture, distribution, origin and evolution of the late Neoproterozoic Tarim Basin by integrating outcrop investigations with well and seismic data. The late Neoproterozoic magma-rich active rifting primarily occurred in the northeastern part of the basin, whereas other areas experienced slightly younger magma-poor passive rifting. The Ediacaran succession overlaps in the northern basement uplift to show a pre-Ediacaran unconformity occurs in the northern Tarim Craton, while a sub-Cambrian unconformity traverses the entire Tarim Craton and presents a distinct truncation in the southern basement uplift. A tiered architecture exists in which narrow, deep Cryogenian grabens are overlain by a broad Ediacaran depression. Two NE-striking rift systems developed in the northeastern and southwestern Tarim. It can be inferred from the compiled data that the late Neoproterozoic rift basin evolution in the Tarim Craton can be divided into four stages: early Cryogenian rifting, late Cryogenian fault-graben, Ediacaran intracratonic depression, and end-Ediacaran regional uplifting. These results suggest that documented Neoproterozoic retreating subduction-related slab failure/detachment processes led to both active and passive rifting, which contributed to the diverse continental rift architecture and evolution of the late Neoproterozoic Tarim Basin.

Late Tonian (ca. 780–750 Ma) bimodal magmatism in the Ogcheon Metamorphic Belt, Korea, at the eastern margin of North China Craton

Neoproterozoic rift-related rocks of the North China Craton (NCC), including the Korean Peninsula, provide crucial information for global supercontinent reconstruction during the Rodinia breakup and Gondwana assembly. Here, we report not only zircon and baddeleyite U-Pb ages but also zircon Hf isotopic and bulk rock compositions of amphibolites in the Ogcheon Metamorphic Belt (OMB), Korea. Zircon occurs as either primary phase or secondary one replacing igneous baddeleyite. Primary zircons analyzed from three amphibolites yielded the weighted mean 206Pb/238U ages of 755 ± 5 Ma (n = 19), 772 ± 3 Ma (n = 9), and 779 ± 13 Ma (n = 12), respectively; this result is corroborated by the baddeleyite age of ∼760–745 Ma. Secondary zircons define discordia lines with lower intercepts corresponding to the Jurassic or Cretaceous age of granites emplaced adjacent to the amphibolite. In conjunction with the occurrence of coeval (ca. 762–745 Ma) metatrachytes, our result suggests that late Tonian bimodal magmatism has lasted for ∼30 m.yr. in the OMB. Moreover, positive εHf(t) values (4.9–21.4) of zircon in amphibolites indicate a depleted mantle source of mafic magma, whereas trace element compositions attest to an intraplate setting for the crystallization. A compilation of Nb-Th and Zr–Zr/Y data suggests that the intraplate setting is also pertinent to ca. 950–750 Ma mafic rocks from the Gyeonggi Marginal Belt, Korea, as well as the NCC. Such a tectonomagmatic correlation is corroborated by detrital zircon age spectra of metasedimentary rocks in the OMB equivalent to those of early Tonian rocks in the NCC. In marked contrast to tectonic scenarios conjecturing a linkage between the OMB and the Nanhua rift, South China Craton (SCC), we conclude that the Ogcheon Belt provides rare geologic-geochronologic evidence for late Tonian breakup of the Rodinia supercontinent at the eastern NCC margin.

Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block, NW China and their geological significance: Constraints from drill cores geochronology and geochemistry studies

As a micro-continent lying at the junction of the North China, Yangtze, and Tarim Cratons in northwest China, the composition and tectonic-thermal history of the Qaidam Block not only are crucial for determining its tectonic attribute and relationships with surrounding cratons, but also can provide key constraints on convergence, fragmentation, and paleogeographic reconstruction of Columbia and Rodinia. In this study, systematic petrology, geochemistry, and zircon U–Pb–Hf isotope analyses were conducted on newly discovered Meso-Neoproterozoic granitic rocks from drill cores in the Qaidam basin and three stages granitic magmatism at ca. 1420 Ma, ca. 900 Ma and 780–750 Ma are yielded. The ca. 1420 Ma granitic rocks exhibit characteristics of highly fractionated I-type granites, with high Yb but low Sr contents, low Sr/Y and La/Yb ratios, high zircon saturation temperatures (774–831 ℃), and positive εHf(t) values (–0.04 to +11.35) with TDM2 values of 2178–1468 Ma, suggesting that they were mainly derived from the ancient crust with mantle magma input under an extensional setting. The ca. 900 Ma granitic rocks have high A/CNK values (1.01–1.21) and variable zircon εHf(t) values (–1.93 to + 6.58) with TDM2 ages between 1402 and 1910 Ma, indicating they are S-type granites formed by partial melting of sedimentary rocks in thickened crust. The ca. 780–750 Ma granites have high Zr + Nb + Ce + Y contents, 10000* Ga/Al ratios, and crystallization temperatures (mean = 808 ℃), belonging to the A1-type granite formed in a continental rift setting.Combined with the previous researches, the Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block can be divided into three stages, 1.8–1.1 Ga, 1.0–0.9 Ga and 850–750 Ma, corresponding to the fragmentation of Columbia, and the assembly and breakup of Rodinia, respectively. Comparing the Qaidam Block with the surrounding blocks and the major cratons in Columbia and Rodinia, it is considered that the Qaidam Block was splited from the Tarim Craton and they may have occupied an interior position in Columbia but a peripheral position in Rodinia, connecting to the India and East Antarctica.

Dynamic evolution of marine productivity, redox, and biogeochemical cycling track local and global controls on Cryogenian sea-level change

The Cryogenian period of the Neoproterozoic was marked by two Snowball Earth glaciations that bookended a non-glacial interval that lasted roughly 10 million years. The break-up of Rodinia in the early Neoproterozoic gave rise to numerous rift basins whose time-varying redox dynamics, linked to marine productivity and biogeochemical cycling, were likely controlled by varying degrees of basin restriction in response to sea-level change. Those drivers were associated with both global glaciations (Sturtian deglaciation and the possibly early onset of the Marinoan) and local tectonics (regional basin uplift/subsidence). To explore these relationships, we focus on the Datangpo Formation, an exceptional shale sequence deposited in a marginal rift basin in South China. The Datangpo succession comprises lower organic-rich black shales and upper organic-lean gray shales/siltstones. As elucidated by our integrated data, the former were deposited in H2S-rich, deep-water settings underlying highly productive surface waters. We attribute this productivity to elevated nutrient supplies replenished from the open ocean following a sea-level rise, as augmented by high terrestrial input of phosphate in the wake of the Sturtian deglaciation. By contrast, the gray shales/siltstones were associated with relatively shallow deposition in an oxic/suboxic water column with suppressed primary production. The major driver of this dramatic shift in water chemistry may lie with a greater extent of basin isolation and the corresponding reduction in nutrient fluxes from the global ocean due to a significant sea-level fall—possibly linked to regional basin uplift. At this time, the basin experienced an elevated influx of detrital clays and organic material, perhaps triggered by lower sea level. Surprisingly, we found that euxinic conditions prevailed in the water column for a substantial period following the onset of more isolated conditions. This relationship can be attributed to redox-dependent phosphorus cycling. Specifically, H2S-replete conditions facilitated regeneration of bioavailable phosphorus, initiating a positive feedback that allowed the persistence of anoxic waters. This study advances our understanding of nutrient cycling and biogeochemical evolution during the Cryogenian under the influence of large-scale sea-level fluctuations and associated time-varying connectivity to the open ocean that must have been common in many basins at this time. Furthermore, our study sheds novel light on the iron proxy and early sulfur cycling. Almost all of the terrestrial silicate-bound iron was likely converted into highly reactive phases due to strong chemical weathering, while sulfur data revealed isotopic stratification in the wake of Sturtian deglaciation, with important messages for interpretations of analogous data in the aftermath of other climate upheavals in Earth history.

Petrology, U-Pb titanite dating and Sr-Nd isotope geochemistry of a shoshonitic lamprophyre dyke near the Western Dharwar Craton-Southern Granulite Terrane contact, southern India: Implications for long-lived enriched mantle, widespread Tonian-Cryogenian rifting, and Rodinia configuration

We present petrology, U-Pb titanite geochronology, bulk-rock and Sr-Nd geochemistry of an undeformed and unmetamorphosed shoshonitic lamprophyre (spessartite) from the Mysuru area (Halaguru- Harohalli alkaline province) located approximately 80 km north of the tectonic contact between the Western Dharwar Craton and the Southern Granulite Terrane, southern India, to understand its origin and to evaluate its geodynamic significance. The lamprophyre shows a typical porphyritic-panidiomorphic texture with amphibole phenocrysts. Clinopyroxene occurs only as xenocrysts with feldspar, apatite, titanite and titano-magnetite confined to the groundmass. Amphibole mineral composition classifies them as pargasite and tremolite, and the groundmass is essentially constituted of alkali feldspar. High whole-rock Mg# (56–65), Ni + Cr (245 to 730 ppm), a lack of correlation between SiO2 and Rb/Sr as well as ɛNd(i) indicates that crustal contamination experienced by the lamprophyre magma is limited. U-Pb titanite (n = 18) SHRIMP-II dating yielded a Neoproterozoic Tera-Wasserburg concordia age of 820 ± 15 Ma (MSWD = 5.9). Whole-rock derived 87Sr/86Sr(i) (0.70425–0.70530) and ɛNd(i) (-6.3 to −4.3) suggest origin of the lamprophyre from an enriched lithospheric mantle source. Paleoproterozoic depleted-mantle model ages of ca. 1.8 Ga suggest the existence of a long-lived enriched mantle which correspond to the timing (ca.1.9–1.7 Ga) of widespread mafic dyke swarms’ emplacement in the Dharmapuri-Agali-Tiruvannamalai domain in the Salem block at the northernmost portion of the Southern Granulite Terrane. The Tonian emplacement age of the studied lamprophyre is synchronous with several co-spatial Neoproterozoic (i) alkaline complexes ± carbonatite ± lamprophyre from the northern part of the Southern Granulite Terrane, and (ii) other mafic alkaline dykes of the Halaguru-Harohalli alkaline province from the southern part of the Eastern Dharwar Craton. Our results highlight the importance of this lamprophyre dyke, present close to the’Fermor Line’ as well as near the boundary between Eastern and Western Dharwar Cratons, which provides a rare opportunity to understand its spatio-temporal link with alkaline dykes of the Southern Granulite Terrain. Our findings also help understand the role of repeated large-scale rifting, associated with the Rodinia break-up, leading to the generation of a wide spectrum of Tonian-Cryogenian alkaline magmas in southern Indian Shield. The new age data also have implications for the configuration of India’s paleoposition during the Neoproterozoic and support the idea that South China Block-India were located on the periphery of Rodinia or were already detached from the supercontinent.