Search Results (62)

This study integrates LA-ICP-MS zircon U–Pb ages and the first zircon trace element data from metasedimentary and metaigneous rocks of the Nyong Complex (NyC) in the NW Congo Craton, southern Cameroon, to constrain its petrogenesis, tectonic setting, and crustal evolution. Chondrite-normalized REE patterns show strong HREE enrichment, depleted LREE–MREE, and pronounced positive Ce and negative Eu anomalies, indicating a magmatic origin for the zircons. Trace element signatures suggest that the zircons derived from continental crustal magmas generated under variable oxidation conditions in a long-lived arc-related tectonic environment. Detrital zircon ages range from Archean to Paleoproterozoic, with five major age peaks at 2885 ± 8 Ma, 2775 ± 6 Ma, 2654 ± 7 Ma, 2469 ± 11 Ma, and 2316 ± 11 Ma. These ages correspond to major magmatic and metamorphic events recognized in both the Congo and São Francisco cratons. The preservation of felsic continental crust between 2.9 and 2.2 Ga in the NyC and the Borborema Province (NE Brazil) likely records a critical transition in Earth’s geodynamic regime, marked by enhanced consumption and recycling of mafic crust during Proterozoic accretion compared to the late Archean. This transition reflects the onset of modern-style plate tectonics, enabling craton stabilization and contributing to the assembly of the Nuna/Columbia supercontinent. The NyC is thus interpreted as part of the Trans-Amazonian belt, analogous to that in NE Brazil, and formed during the collision between the Congo and São Francisco cratons. Full article

To reveal the evolution of the North China Craton (NCC) and the breakup process of the Columbia supercontinent, this study conducted zircon geochronology and garnet mineralogical analyses on kimberlites from the Bayan Obo area, on the northern margin of the NCC. Zircon U-Pb dating yielded four groups of concordant ages: 2505 ± 46 Ma, 2210 ± 57 Ma, 1928 ± 58 Ma, and 1455 ± 88 Ma. Among these, 1455 ± 88 Ma represents the formation age of the kimberlite, corresponding to a regional extensional tectonic setting. The other three groups are xenocrystic zircon ages, recording the formation of the Archean basement of the NCC, extensional magmatic activity in the middle Paleoproterozoic, and collisional metamorphic events in the late Paleoproterozoic, respectively. The major element characteristics of the garnets indicate they are granulite-facies crust-derived garnets (G4 type), formed under temperature and pressure conditions of 791 ± 50–876 ± 50 °C and 14 ± 3.0 kbar. This corresponds to a mantle heat flow value of approximately 60 ± 5 mW/m², suggesting an unstable state of the lithosphere in the study area. Combined with the regional geological background, the depositional age of the Bilute Formation in Bayan Obo is determined to be between 1455 and 1524 Ma. The emplacement of kimberlite is related to extensional rifting driven by the breakup of the Columbia supercontinent, and garnets hosted in kimberlite record the crustal extension and mantle magma underplating during the rift-spreading stage of this period. This study provides key petrological and chronological evidence for the tectonic evolution of the northern margin of the NCC and the breakup of the Columbia supercontinent. Full article

Mid-Neoproterozoic magmatism provides important constraints for revealing the break-up history of the Rodinia supercontinent. Large-sized mid-Neoproterozoic magmatic rocks are distributed within the Dabie Orogen located on the northern Yangtze Block. This study performed zircon LA-ICP-MS geochronology, whole-rock major and trace elements, and zircon Lu-Hf isotope analyses on orthogneisses with a mid-Neoproterozoic protolith age of the northern Dabie Orogen. The analysis results show that the intrusion times of mid-Neoproterozoic granitoids and mafic rocks are all ~750 Ma, with ε_Hf(t) values ranging from −6.60 to −2.57 and a two-stage Hf model age of ~1.8 Ga. They are characterized by light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion. In the primitive mantle-normalized trace element diagram, these rocks are enriched in La, Ce, Th, K, Zr, Nd, and Sm and depleted in Nb, Ta, P, Ti, and Sr, with negative Eu anomaly or no significant Eu anomaly. Based on the discrimination diagrams, most of the samples are plotted into the A-type granite field, and which was formed in a post-orogenic extension setting. Comprehensive analysis shows that these mid-Neoproterozoic magmatic rocks were produced by melting of juvenile crust of the Paleoproterozoic and late Mesoproterozoic, having a heterogeneous distribution of δ¹⁸O, indicating that these rocks were developed mainly through high-temperature meteoric-hydrothermal alteration during syn-rift magmatic activity. Full article

The early crustal evolution of microcontinental fragments in the Central Asian Orogenic Belt remains poorly constrained. Among these fragments, the Erguna Block records extensive Neoproterozoic magmatism that provides key constraints on its tectono-magmatic development in relation to the Rodinia supercontinent cycle. To furthering constrain the Neoproterozoic magmatic evolution of the Erguna Block, an integrated investigation combining petrography, zircon U-Pb and Lu-Hf isotopic analyses, whole-rock geochemistry, and Sr-Nd isotope data was carried out on the newly recognized Fengshuishan intrusion in northern Alongshan. Zircon U-Pb ages of 810 ± 5 Ma and 807 ± 4 Ma were obtained from granitic samples, while the dioritic sample gave an age of 773 ± 2 Ma, representing a major Neoproterozoic magmatic episode. The 810–807 Ma granites show positive zircon εHf(t) (+0.09 to +12.1) and whole-rock εNd(t) (+0.50 to +1.77), suggesting derivation mainly from partial melting of Mesoproterozoic juvenile crust with minor contribution from mantle-derived materials. In contrast, ca. 773 Ma gabbroic diorite exhibits εHf(t) values of −1.23 to +4.3 and an εNd(t) value of +1.33, implying a contribution from an enriched mantle source. These Fengshuishan igneous rocks show A-type geochemical signatures, enriched in Rb, Th, and Pb but depleted in Ba, Sr, and Eu. Integrating these data with regional geological evidence, we infer that the Fengshuishan intrusion formed in an intraplate extensional regime, recording an important phase of crust–mantle interaction during the Neoproterozoic. These results expand the record of Neoproterozoic igneous rocks in the Erguna Block and offer new constraints on its role within the Rodinia supercontinent. Full article

The Yangtze Block provides a natural window into the tectonic evolution of Precambrian continental crusts. The Julin Group is a dominant Precambrian stratigraphic unit in the southwestern block, the depositional age of which is still poorly constrained. The lowest sequence of this group, the Pudeng Formation, is primarily composed of mica-quartz schists and quartzites intruded by a biotite monzogranite. LA–ICP–MS zircon U-Pb ages of biotite monzogranite and detrital zircons constrain the deposition of the Julin Group to between 1099 and 1052 Ma. Geochemical compositions of the mica-quartz schists and quartzites display high δCe, ΣREE, Th/Sc, and Th/U, along with low δEu, La/Sc, Ce/Th, and Al₂O₃/(Al₂O₃ + Fe₂O₃) ratios, indicating their derivation from felsic volcanic protoliths in a passive continental margin setting. The detrital zircons show distinct age peaks at 2.5, 1.85, and 1.6 Ga, with their source regions primarily located along the western and northern Yangtze Block. Integrating the magmatic records within the Yangtze Block with the ages and ε_Hf(t) values of detrital zircons indicates that the tectonic setting of the western Yangtze Block evolved from a subduction-related arc at ~2.5 Ga to an orogenic belt at ~1.86 Ga and subsequently to intracontinental extensional (rift) environments at ~1.6 Ga and ~1.2 Ga. This evolution reflects the geodynamic transition from the Arrowsmith orogeny to the assembly and development of the Columbia and Rodinia supercontinents. Full article

Fluvio-lacustrine systems are highly dynamic continental environments, often developing in tectonically controlled, endorheic basins where sedimentation reflects the interplay of fluvial processes, lake-level fluctuations, climate, and subsidence. The main aim of this paper is to reconstruct the depositional architecture and paleogeographic evolution of the Ludwikowice Formation (Intra-Sudetic Basin, NE Bohemian Massif), which preserves a high-resolution record of a late Carboniferous (late Gzhelian) fluvio-lacustrine system. The formation developed as a fining-upward megacyclothem documenting the transition from proximal alluvial and fluvial fan deposits to distal, organic-rich lacustrine facies referred to as the Lower Anthracosia Shale (LAS). This study integrates lithological data from 92 archival boreholes with high-resolution sedimentological, geochemical, petrological, palynological, and magnetic susceptibility analyses from two fully cored reference sections (Ścinawka Średnia PIG-1 and Rybnica Leśna PIG-1) and selected exposures. Nine facies associations (FA1–FA9) have been identified within the formation, including fluvial, sandy to muddy floodplain, aeolian, playa lake margin/coastal mudflat, nearshore, delta plain, subaqueous delta front and subaqueous fan, prodelta, and open lake. The succession shows progressive thickening into narrow, NW–SE-trending depocenters associated with possible strike-slip faulting. Geochemical and isotopic data indicate alternating hydrologically open and closed lake conditions, while magnetic susceptibility reflects climatically driven variations in detrital influx and microbial activity. Organic petrography and palynofacies analyses reveal redox-controlled maceral associations. The Ludwikowice Formation constitutes a detailed archive of Late Paleozoic environmental change and provides new insights into sedimentation and organic matter preservation in intramontane endorheic basins. Our results highlight the response of fluvio-lacustrine systems to climatic and tectonic factors and provide a framework for interpreting analogous successions throughout the stratigraphic record. Full article

Megacrystalline uraninite within Neoproterozoic migmatites in the Haita area of the Kangdian region of China provides a unique condition for the investigation of uraninite typomorphism under high-temperature conditions. The present study represents the first systematic characterization of the typomorphic signatures and genetic significance of megacrystalline uraninite via optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XRS), and electron probe microanalysis (EPMA). The results show that uranium mineralization occurs as euhedral megacrystalline uraninite (black grains ≤ 10 mm) hosted in quartz veins, exhibiting frequent rhombic dodecahedral and subordinate cubic–octahedral morphologies. The paragenetic assemblage is quartz–uraninite–titanite–apatite–molybdenite. The investigated uraninite is characterized by elevated unit-cell parameters and a reduced oxygen index, with complex chemical compositions enriched in ThO₂ and Y₂O₃. These typomorphic characteristics indicate crystallization under high-temperature reducing conditions with gradual cooling. Post-crystallization tectonic fragmentation and uplift-facilitated oxidation occur, generating secondary uranium minerals with concentric color zonation (orange–red to yellow–green halos). Mineralization was jointly controlled by migmatization and late-stage tectonism, with the breakup of the Rodinia supercontinent serving as the key driver of fluid mobilization and ore deposition. The data materialized in the present study improve our knowledge about uranium mineralization during continental breakup events. Full article

The nocturnal, flightless camel crickets (Rhaphidophoridae) have a global distribution and are believed to have originated prior to the breakup of Pangea. We investigated the phylogeny and the timing of the radiation of East Asian species with mitogenomic data. Initially we analyzed a large taxon dataset (n = 117) using available partial mitochondrial and nuclear DNA sequences to confirm the monophyly of subfamilies and current taxonomy. Our findings support the monophyly of each genus within the subfamily Aemodogryllinae, with a minor inconsistency between taxonomy and phylogeny resolved by resurrection of the genus Gymnaeta Adelung. Fossil-calibrated molecular clock analysis used 11,124 bp alignment of 13 complete mitochondrial protein-coding genes for 20 species of Rhaphidophoridae, with a focus on the neglected Rhaphidophorinae and Aemodogryllinae lineages. Divergence time estimates suggest that the most recent common ancestor of the family lived during the Early Jurassic (189 Mya ± 23 Mya) before Pangea broke into the supercontinents or possibly during the early stage of breakup when Gondwana and Laurasia were still connected by land. The two subfamilies, Rhaphidophorinae and Aemodogryllinae, that overlap in Asia are estimated to have diverged 138 Mya ± 17 Mya, well before the Late Cretaceous northern connection between America and Asia (the Bering Land Bridge). Thus, our extended sampling of species from East Asia and Oceania refutes the importance of continental drift in the evolution of this wingless orthopteran family. Full article

The Yangzhuang Formation of the Mesoproterozoic Jixian System exhibits a well-developed carbonate sedimentary sequence. However, the carbonate cycles within the Yangzhuang Formation and their co-evolution with paleoclimate and paleoceanographic environment changes remain insufficiently studied. This study conducts a systematic investigation of the rhythmic layers of the Yangzhuang Formation within the Yanshan Basin, North China, through major and trace element analysis, rare earth element analysis, inorganic carbon isotope analysis, granulometric analysis, and time series analysis. The results show that the low content of terrigenous clastics (11.2%~32.6%), slow sedimentation rate (2.2–2.5 cm/ka), Mg/Ca molar ratio close to 1 (1.05–1.53), and small fluctuation of δ¹³C_carb (−0.37‰~−0.05‰) in Member 3 of the Yangzhuang Formation constitutes the processes of co-evolution, along with a mid-phase fluctuation. It indicates the stable evolution of the sedimentary environment and slow ocean expansion speed. However, there is a fluctuating characteristic affected by the breakup of the Colombian supercontinent. The chemical and granulometric analysis of the red and gray layers shows that the terrigenous materials are mainly derived from the eolian sediments, with differences in the wind carrying materials. The time series analysis of the dense samples displays the coupling between the rhythm of the red and gray layers, the inorganic carbon isotope cycle, and the 15 ka precessional cycle in the Mesoproterozoic. We conclude that the rhythm of layers is mainly affected by the monsoon change driven by low-latitude solar radiation at that time, and the age of the Yangzhuang Formation is limited to 1550~1520 ± 2 Ma. The study of the Mesoproterozoic sequence using geochemical data from carbonate deposits reveals the underlying mechanism of global co-evolution during this period, providing a basis for understanding the evolution of the Mesoproterozoic Earth system. Full article

The Luanchuan Neoproterozoic gabbroic intrusions are located at the southern margin of the North China Craton (NCC), intruding into the marble and schist from the Nannihu and Meiyaogou Formations of the Neoproterozoic Luanchuan Group. The gabbroic rocks consist of plagioclase (30%–50%) and amphibole (40%–60%), with minor ilmenite (2%–5%), biotite (1%–3%), and titanite (~1%). Based on the occurrence and mineral chemistry, two types of biotites were identified. The first type of biotite (Bt I) is brown, with a fine- to micro-grained anhedral texture, occurring around the magmatic ilmenite and coexisting with titanite. Bt I is characterized by high TiO₂ and FeO contents, with TiO₂ > 2 wt% (2.03 wt%–3.15 wt%) and FeO ranging from 19.94 wt% to 22.08 wt%. The other type of biotite (Bt II) is light grayish-brown to dark reddish-brown, with a medium- to coarse-grained euhedral texture, coexisting with grayish-green amphibole. Bt II exhibits lower TiO₂ (1.40 wt%–1.90 wt%) and FeO contents (18.03 wt%–21.42 wt%). The K₂O (7.56 wt%–9.32 wt%) and SiO₂ (34.49 wt%–37.04 wt%) contents of Bt I are slightly lower than those of Bt II (8.28 wt%–9.73 wt% and 35.18 wt%–37.52 wt%, respectively). Despite the low Ti content in biotites, the mineral occurrence indicates that both types of biotite yield a magmatic origin, resulting from the reactions between early crystallized minerals and residual magma. Bt I originated from the reaction between ilmenite and residual magma, while Bt II resulted from the production of the reaction between clinopyroxne and residual magma. Ilmenite exhibits low MgO and Fe₂O₃ contents but high FeO and MnO contents, suggesting genetic similarities to the Skaergaard and Panzhihua intrusions. Both types of biotites record consistent temperatures (T = 766 to 818 °C), pressures (P = 5.30–8.80 kbar), and oxygen fugacities (log fO₂ = −12.35 to −14.06), aligning with those of the Fanshan complex and the Falcon Island intrusion. The mineralogy of ilmenite and biotite indicates that the Luanchuan gabbroic intrusions formed in a continental rift setting, which is considered to be associated with the breakup of the Rodinia supercontinent. Full article

Clouds play a central role in regulating incoming solar radiation and outgoing terrestrial emission; hence, they must be internally constrained to prognose Earth’s temperature. At the same time, planetary fluids are inherently turbulent, so the climate state would tend toward maximum entropy production—a generalized second law of thermodynamics. Incorporating these requirements, I have previously formulated an aquaplanet model to demonstrate that intrinsic water properties may strongly lower the climate sensitivity to solar irradiance, thereby resolving the faint young Sun paradox (FYSP). In this paper, I extend the model to include other external forcings and show that sensitivity to the reduced outgoing longwave radiation by the elevated pCO₂ can be several times greater, but the global temperature remains capped at ~40 °C by the exponential increase in saturated vapor pressure. I further show that planetary albedo augmented by a tropical supercontinent may cool the climate sufficiently to cause tropical glaciation. And since the glacial edge is marked by above-freezing temperature, it abuts an open, co-zonal ocean, thereby obviating the “Snowball Earth” hypothesis. Our theory thus provides a unified framework for interpreting Earth’s diverse climates, including the FYSP, the warm extremes of the Cambrian and Cretaceous, and the tropical glaciations of the Precambrian. Full article

Post-collisional volcanism provides valuable insights into mantle dynamics, crustal processes, and mechanisms driving orogen uplift and collapse. This study presents geological, geochemical, and geochronological data for Ediacaran effusive and pyroclastic units from the Taghdout Volcanic Field (TVF) in the Siroua Window, Anti-Atlas Belt. Two eruptive cycles are identified based on volcanological and geochemical signatures. The first cycle comprises a diverse volcanic succession of basalts, basaltic andesites, andesites, dacites, and rhyolitic crystal-rich tuffs and ignimbrites, exhibiting arc calc-alkaline affinities. These mafic magmas were derived from a lithospheric mantle metasomatized by subduction-related fluids and are associated with the gravitational collapse of the Pan-African Orogen. The second cycle is marked by bimodal volcanism, featuring tholeiitic basalts sourced from the asthenospheric mantle and felsic intraplate magmas. These units display volcanological characteristics typical of facies models for continental basaltsuccessions and continental felsic volcanoes. Precise CA-ID-TIMS U-Pb zircon dating constrains the volcanic activity to 575–557 Ma, reflecting an 18-million-year period of lithospheric thinning, delamination, and asthenospheric upwelling. This progression marks the transition from orogen collapse to continental rifting, culminating in the breakup of the Rodinia supercontinent and the opening of the Iapetus Ocean. The TVF exemplifies the dynamic interplay between lithospheric and asthenospheric processes during post-collisional tectonic evolution. Full article

Precambrian tropical glaciation is an enigma of Earth’s climate. Overlooking fundamental difference of land/sea icelines, it was equated with a global frozen ocean, which is at odds with the sedimentary evidence of an active hydrological cycle, and its genesis via the runaway ice–albedo feedback conflicts with the mostly ice-free Proterozoic when its trigger threshold was well exceeded by the dimmer sun. In view of these shortfalls, I put forth two key hypotheses of the tropical glaciation: first, if seeded by mountain glaciers, the land ice would advance on sea level to be halted by above-freezing summer temperature, which thus abuts an open cozonal ocean; second, a tropical supercontinent would block the brighter tropical sun to cause the required cooling. To test these hypotheses, I formulate a minimal tropical/polar box model to examine the temperature response to a varying tropical land area and show that tropical glaciation is indeed plausible when the landmass is concentrated in the tropics despite uncertain model parameters. In addition, given the chronology of paleogeography, the model may explain the observed deep time climate to provide a unified account of the faint young Sun paradox, Precambrian tropical glaciations, and Phanerozoic glacio-epochs, reinforcing, therefore, the uniformitarian principle. Full article

The Indo-Burma Range (IBR), as one of the youngest accreted units in the Eastern Neotethys, plays a crucial role in understanding the interactive relationships between the Gondwana supercontinent and its rifted microcontinents in SE Asia. However, its basement nature and tectonic evolution remain debated. Here, we conducted a comprehensive structural analysis across six sections within the IBR and correlated Late Triassic flysch units between the Western IBR (Pane Chaung Formation) and the Tethyan Himalaya. Within the Mindat section, the eastern segment of the Pane Chaung Formation unit displays top-to-east vergent overturned folds, indicating eastward backthrusting, in contrast to the prevailing top-to-west vergence structures in Kalemyo, Natchaung, Magwe and the western segment of the Mindat flysch unit. By reconstruction of this backthrust sheet, a megathrust separates the Pane Chaung Formation unit in the footwall to the west from schist units in the hanging wall to the east. The Pane Chaung Formation unit in the Western IBR and its counterparts in the Tethyan Himalaya share common characteristics, including herringbone cross-beddings, Carnian–Norian Halobia fossils, and dominant detrital zircons of 220–280, 500–620, 900–1000, and 1100–1140 Ma. Alongside the Paleozoic strata and Precambrian one-stage model ages of Mesozoic dikes, as evidenced by ɛ_Nd (t) (−13.4 to −0.1) and ɛ_Hf (t) (−24.2 to −0.1) in the Tethyan Himalaya, these facts suggest that the major tectonic units of the Western IBR–Tethyan Himalaya are the result of the amalgamation of a microcontinent with the West Burma Block. The transition from OIB to E-MORB and N-MORB, the rapid deepening of sedimentary waters, and the presence of the 155–152 Ma Indian ocean crust collectively indicate that the microcontinent rifted from the host East Gondwana as a fragment of the Argoland archipelago in the Late Jurassic. This identification sheds light on the orogenic processes of the doublet subduction zones in the Indo-Myanmar orogenic belt. Full article