The tectonic evolution of central Tibet was shaped by multiple collisions, notably the Cretaceous collision between the Lhasa and Qiangtang terranes and the subsequent India-Asia collision. Yet, uncertainties in the Early Cretaceous paleogeography of the Lhasa terrane still obscure their timing and mechanisms. Here we present new paleomagnetic data derived from Early Cretaceous sedimentary and volcanic sequences in the northern Lhasa terrane. Field tests, rock magnetic experiments, and petrographic analyses demonstrate that the characteristic remanent magnetizations are primary. Sedimentary rocks show shallower mean directions than volcanic rocks, but Elongation-Inclination analysis effectively corrects this bias, producing consistent paleomagnetic estimates. The combined dataset defines a paleomagnetic pole at 68.6 degrees N, 348.7 degrees E (A(95) = 1.4 degrees), indicating a paleolatitude of 25.5 degrees +/- 1.4 degrees N for the Bangoin region during the interval of 114-113 Ma. Comparison with the Asian apparent polar wander path suggests 560 +/- 200 km of intracontinental shortening since the late Early Cretaceous. Integrated with published paleomagnetic data and geological evidence, these findings indicate that the central and eastern Lhasa terrane had already collided with the Qiangtang terrane at approximately 30 degrees N by similar to 114 Ma, with subsequent westward propagation of the collision. Moreover, during the late Early Cretaceous, the southern margin of Asia was situated at a paleolatitude exceeding 20 degrees N, in contrast to the coeval low-latitude setting (<= 10 degrees N) of the Trans-Tethyan Subduction Zone. This significant paleolatitudinal disparity supports an intra-oceanic equatorial arc-continent collision at similar to 55 Ma and provides new constraints on the timing and geodynamic mechanisms of the India-Asia collision.

Understanding the timing and magnitude of deformation in the Tangula Range is crucial for elucidating the topographic growth of central Tibet. The Yanshiping region, located in the central Tangula Range, comprises Permian to Miocene sedimentary rocks that record the Tangula Range's deformational history since the Mesozoic. Our study presents new geological maps, balanced cross-sections, and low-temperature thermochronology results, shedding light on the deformational history of the Yanshiping region. The balanced cross-section reveals a north-verging fold-thrust belt accommodating at least 90 km of crustal shortening (>49 %) post-Jurassic deposition. Sedimentological and thermochronological data suggest substantial crustal shortening occurred at 60-35 Ma, likely driven by the India-Asia collision and related continental subduction. Integrating our results with previous studies, we infer that central Tibet's topographic evolution included a broad Central Tibetan Valley during similar to 96-60 Ma and a narrower valley during similar to 60-35 Ma.

Subduction-related crustal thickening and associated surface responses are key to understanding how continental interiors evolve into high plateaus. The Qiangtang Basin, as a major component of the proto-Tibetan orogenic system, preserves critical sedimentary and geochemical records of this transition. Here we integrate sedimentological, stratigraphic, petrographic and detrital zircon U-Pb and trace element data from the Late JurassicEarly Cretaceous Xueshan Formation to reconstruct the paleogeography and crustal evolution of central Tibet. The Xueshan Formation comprises conglomerates, pebbly sandstones, mudstones, and minor limestones deposited in tidally influenced delta-fan delta environments, marking the transition from shallow marine to fluvial environments. Maximum depositional ages of 157-148 Ma indicate predominantly Late Jurassic sedimentation. Provenance analysis reveals that the Qiangtang Metamorphic Belt was the dominant sediment source, supplemented by variable input from the uplifted southern Qiangtang terrane, whereas the Hoh-Xil-SongpanGanze complex remained topographically stable. The youngest volcanic components were derived from Late Jurassic magmatic rocks. Detrital zircon Eu anomalies and whole-rock geochemistry indicate progressive crustal thickening of the source area from similar to 50 to >70 km between similar to 168 and 145 Ma. This thickening and associated uplift reflect the transition from a plate-margin to an intracontinental orogenic regime, driven by flat-slab subduction of the Bangong-Nujiang Tethys lithosphere. The resulting topography established a proto-Tibetan highland that likely served as the headwater for transcontinental drainage toward Southeast Asia. These findings highlight that lithospheric reorganization and surface uplift within the Eurasian interior began prior to the Cenozoic India-Asia collision, offering broader insights into how deep Earth processes shape continental topography and global mountain-building systems.

The Fen Wei Graben System, a Cenozoic intracontinental rift basin dominated by far-field tectonic stress in China, hosts abundant geothermal resources, with carbonate formations serving as important geothermal reservoirs for exploration and development. This study aims to clarify the formation mechanisms and to quantify the resource potential of typical geothermal fields within the graben to inform exploration and sustainable utilization. By compiling drilling and production data, temperature-depth profiles, synthesized hydrochemistry and stable-isotope datasets, this study identifies that convective and conductive heat transfer coexist as two dominant modes in different basins, and establishes three end-member conceptual models: 1) conduction-dominated model with lateral recharge, 2) convection-dominated model with vertical heating, and 3) conduction-dominated model with confined paleo-water. Quantitatively, the combined geothermal resources of the three fields reach 14.3 & times; 10(9) GJ, equivalent to 486 & times; 10(6) t of standard coal; under balanced extraction-reinjection conditions, the annual allowable fluid production totals 134 & times; 10(6) m(3) and the corresponding producible heat is 22.9 & times; 10(6) GJ/a. Extrapolated to basin scale, the carbonate reservoirs of the Jinzhong, Linfen-Yuncheng, and northern Weihe basins could meet similar to 118 & times; 10(6) m(2) of heating demand, demonstrating significant development potential. These findings provide a process-based framework and quantitative benchmarks for prioritizing high-potential targets in the Fen Wei Graben System and analogous intracontinental rifts. (c) 2026 Sinopec Petroleum Exploration and Protection Research Institute. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The Deccan Traps eruptions significantly impacted Earth's climate and ecosystems from the Late Cretaceous to early Paleogene periods, contributing to mercury (Hg) enrichments in global sediments. However, Hg signals from East Asia exhibit considerable variability across different lake basins. Here, we present high-resolution Hg records from continuous terrestrial sediments in the Jiaolai Basin, eastern China, and integrate them with other East Asian records to investigate the causes of these discrepancies. Our results reveal significant Hg enrichments both before and after the Cretaceous-Paleogene boundary, with positive Delta Hg-199 and near-zero to slightly negative delta Hg-202 values, indicating long-distance atmospheric transport of volcanogenic Hg linked to the second and third Deccan eruptive pulses. By comparing Hg signals across East Asia, we highlight that local climate and depositional conditions strongly influenced Hg transport and accumulation. The integrated Hg records from East Asia provide a more comprehensive view of the first three major Deccan eruptions. The significant Hg enrichments, along with the elevated pCO(2) and temperature before biotic recovery, suggest that the third Deccan pulse, rather than the fourth, played a critical role in driving climatic disruptions and delaying ecosystem recovery during the early Paleogene.

The Qiangtang Basin, the largest Mesozoic marine hydrocarbon-bearing basin in China, has long been at the center of debate regarding the formation age of its principal source rocks. In this study, we apply in situ LA-ICP-MS calcite U-Pb geochronology for the first time, integrated with cathodoluminescence imaging and geochemical analyses, to provide precise chronological constraints on their formation. The results indicate that the limestone interbeds within the Xichangliang-Shenglihe oil shale of the Northern Qiangtang Depression yield ages of 164–163 Ma (Callovian, Middle Jurassic), revising the previously inferred Late Jurassic-Early Cretaceous age based on Re-Os data. In contrast, the Amdo 114 Station source rock in the Southern Qiangtang Depression yields ages of 168–165 Ma (late Bathonian to Callovian, Middle Jurassic), consistent with calcareous nannofossil evidence and published U-Pb ages (166–164 Ma) from the Biluo Co oil shale. Collectively, these results together with seismic reflection and paleogeography demonstrate that these three major source rocks were deposited contemporaneously during the late Bathonian-Callovian, indicating a widespread, high-quality Middle Jurassic source rock system developed across the Northern Qiangtang Depression. This study establishes a robust, high-precision geochronological framework that resolves the long-standing controversy over the timing of source-rock formation. We propose that these high-quality source rocks were developed under warm, semi-arid paleoclimatic conditions, where regional evaporitic restriction and elevated salinity likely enhanced organic matter preservation within a stratified water column.

ABSTRACT While previous studies have reported a link between provenance changes and the tectonic–paleogeographic evolution of basins in the North China Craton (NCC) and the Qinling Orogenic Belt during the late Palaeozoic, the mechanisms of the provenance transition and tectonic–paleogeographic evolution of the southeastern margin of the NCC and its adjacent basins remain unclear. To investigate the tectonic processes that were responsible for the provenance changes, we conducted a detailed study of the Carboniferous–Permian successions sampled from a drill hole in the Huainan Coalfield, such as sandstone petrology, U–Pb geochronology of detrital zircon grains in sandstones using LA–ICP‐MS, and Lu–Hf isotope analysis. The Qt–F–L plots suggest that except for the provenance of the Benxi Formation, which was mainly continental arc, the overlying Formations (Taiyuan, Shanxi, Xiashihezi, and Shangshihezi) were predominantly derived from volcanic‐magmatic arc, indicating a shift in sediment source from a recycled orogenic belt for the Carboniferous units to a volcanic‐magmatic arc for the Permian units. The ZTR values in the overlying Formations are significantly higher than that in the Benxi Formation, reflecting an increase in mineral maturity and longer transport pathways. Detrital zircon age patterns and Ɛ Hf ( t )‐age plots suggest zircon ages in the Benxi Formation are predominantly Neoproterozoic to Mesoproterozoic, whereas those in the overlying Formations are mainly Late Palaeozoic, with overall negative Ɛ Hf ( t ) values, reflecting clear changes in the source. The tectonic evolution model of the NCC during the late Palaeozoic was reconstructed using the above analyses and the existing paleogeographic framework of the area. In the late Carboniferous, subduction of the Mianlue Ocean plate beneath the Qinling Orogenic Belt started and led to uplift and erosion of the North Qinling Orogenic Belt, resulting in a north–south elevation gradient in the North China region. In the early to middle Permian, accelerated subduction of the Paleo‐Asian oceanic plate led to rapid uplift of the northern flank of the NCC, forming the Yinshan–Yanshan and Xingmeng orogenic belts. The significant influx of distal sediments and cyclicity of sedimentary provenance in the Huainan region record the uplift and erosion of the Qinling Orogenic Belt, and reconstruction of these changes is crucial for a comprehensive understanding of the late Palaeozoic sedimentary processes and tectonic–paleogeographic evolution of North China.

ABSTRACT Dyke swarms preserve both emplacement geometry and subsequent tectonic overprints, providing valuable constraints on crustal kinematics. Here, we re‐evaluate Late Cretaceous tectonic rotation in the Eastern Gangdese belt of the Lhasa terrane, southern Tibet, by applying the net tectonic rotation (NTR) method to published palaeomagnetic and structural data. The preferred solution indicates a 26.2° counterclockwise vertical‐axis rotation about a pole at D = 133.7° and I = 38.1°, while restoring the dykes to near‐vertical initial orientations. This estimate is slightly larger than previous tilt‐corrected results, reflecting the tighter geometric constraints imposed by the NTR framework through the joint restoration of magnetization vectors and dyke orientations. We interpret the observed rotation as the cumulative result of multiple tectonic processes associated with India–Asia convergence, most plausibly including Late Cretaceous Neo‐Tethyan oblique convergence and later distributed intracontinental strike‐slip deformation. Our results provide a new quantitative constraint on the kinematic evolution of southern Tibet and further demonstrate the value of dyke‐based NTR analysis for reconstructing tectonic deformation in structurally complex orogenic systems.

Post-collisional magmatic records (e.g., Oligocene-Miocene adakitic, potassic, ultrapotassic, and mafic rocks) in southern Tibet provide a unique insight into deep geodynamic processes beneath the Tibetan-Himalayan Orogen. However, the triggering mechanism and accompanied asthenosphere-lithosphere interaction for post-collisional magmatism still remain ambiguous. In this study, we present a combination of geological, petrological, geochronological, geochemical, and isotopic data for newly-identified Middle Miocene basaltic rocks in the Zhari and Kongmeda areas in the Yarlung-Tsangpo Suture Zone (YTSZ). The Zhari and Kongmeda basaltic rocks have a medium-K trachybasalt affinity and oceanic island basalt (OIB)-type geochemical characteristics with moderate La-N/Yb-N ratios (6.69-17.82 and 5.18-8.90) and slightly positive Nb-Ta-Ti anomalies. They also show relatively depleted SrNd isotopic compositions with initial Sr-87/Sr-86 (0.7058-0.7064, 0.7082-0.7092) and positive epsilon(Nd)(t) (+2.7 to +3.1, +1.2 to +2.4). Geochemical signatures and modeling results demonstrate that the Zhari and Kongmeda basaltic rocks were most likely generated by low-degree partial melting of asthenospheric mantle sources at or slightly below the similar to 75-85-km-deep garnet-spinel transition zone, along with minor involvements of lithospheric mantle components during magma ascent, implying asthenospheric upwelling and resultant asthenosphere-lithosphere interaction beneath the western YTSZ. Based on large-scale spatiotemporal analysis of post-collisional magmatic records in southern Tibet, the E-W-trending post-collisional magmatic zone with bidirectional center-ward younging trend was predominantly triggered by the bilateral tearing and detachment of the subducted Indian continental slab, along with minor effects from its longitudinal tearing, during the Oligocene-Miocene.

Deep coalbed methane (CBM) is an important frontier for expanding unconventional natural gas reserves and production in China. Significant vertical heterogeneity in coal reservoirs is a primary constraint on exploration and development, and the conventional interval subdivision based solely on burial depth is insufficient for refined evaluation of deep coal reservoirs. This study targets the No. 8 coal seam of the Carboniferous Benxi Formation in the northern part of the eastern margin of the Ordos Basin. Based on core and logging data from wells F and S, this study applies the Milankovitch cycle identification method and uses the short-eccentricity cycle (∼109 kyr) as a working timescale for high-resolution isochronous stratigraphic subdivision of coal seams within a single well. Combined with coal petrology and reservoir property analysis and the Analytic Hierarchy Process (AHP), this study characterizes vertical heterogeneity and quantitatively identifies favorable intervals in the coal reservoir. The results indicate that: (1) the No. 8 coal seam in Well F was divided into three sections, and Well S into two sections. These subdivisions provide a high-resolution cyclostratigraphic framework for evaluating vertical reservoir variations within each well, with higher resolution than conventional depth-based segmentation (spectral confidence > 99%, p < 0.01); (2) coal quality, pore structure, and gas potential vary significantly with depth, and these variations represent geological responses to periodic changes in depositional environment and sediment supply during peat accumulation; (3) AHP-based quantitative evaluation identifies the upper section of Well F (score: 0.336) and the lower section of Well S (score: 0.755) as the favorable targets for the two investigated wells, characterized by good coal quality, favorable pore structure, and high gas storage capacity. These findings provide geological support for refined deep coalbed methane exploration and development in the study area, and also offer a new technical approach for high-precision stratigraphic subdivision of coal reservoirs.

In this paper, 23 species of 14 genera within the melange of the Saga area are documented. On this basis, a stratigraphic correlation is established between the Tethys Himalaya and the Yarlung-Tsangpo suture zone. The Cretaceous siliceous rock and siliceous mudstone strata in the melange are also reported. Six stratigraphic units are identified in the Tethys Himalaya (Jurassic Zhela and Weimei formations, Cretaceous Rilang, Duobeng and Chuangde formations, and Paleocene Sangdanlin Formation). The Early Cretaceous radiolarians from the melange and the deep-water sediments of the passive continental margin in the Rilang and Duobeng formations both indicate that during the Early Cretaceous, the Neo-Tethys Ocean was a widespread deep-sea environment. The reconstructed strata in this study are considered to have been deposited contemporaneously with the Rilang and Duobeng formations. In other words, while the Rilang and Duobeng formations were deposited along a passive continental margin, the deposition of the siliceous deep-water and hemipelagic sediments occurred in the ocean. After the Early Cretaceous, these sediments were preserved as accretionary melange, becoming part of the Yarlung-Tsangpo suture zone. (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The heterogeneous Tibetan lithosphere has led to the formation of distinct geomorphic units on the plateau surface over the past ~250 Myr. One prominent topographical feature is the delineation of intervening sedimentary basins by high mountain belts. Unlike the high and rugged Kunlun, Gangdese and Himalaya Mountains, the Central Tibet Watershed Mountains (CTWM) in the Qiangtang terrane exhibit a relatively low relief of ~1 km or less compared with surrounding basins. They are important geological and geographical barriers with perspectives on the formation process that are subject to dispute. The outburst of detrital zircon geochronology data sets in the Qiangtang basin provides an opportunity to address this issue. The combination of inverse and forward modeling of 6197 detrital zircon U-Pb ages enables the establishment of provenance mapping, which averts tedious descriptions of individual age modes. Integrated with petrographic analysis and paleocurrents, the provenance of the Jurassic Qiangtang basin is quantitatively constrained. The CTWM remained consistently significant sources throughout the Jurassic time. Internal sources of Triassic and Jurassic magmatic rocks locally supplied younger zircon grains. The source proportion of the Hoh Xil- Songpan Ganze (HSG) terrane increased across the basin in the Middle Jurassic but decreased dramatically in the Southern Qiangtang in the Late Jurassic. Contextualized in geological details, an embryonic watershed that separates rivers flowing into the Pacific and Indian oceans formed in central Tibet during the Late Jurassic.

ABSTRACTThe Central Tibet Watershed Mountains (CTWMs) are located in the hinterland of the Tibetan Plateau, extending over 1000 km from west to east. These mountains currently function as a drainage divide, separating Tibet's rivers into eastward‐ and southward‐flowing systems to the north and the south of the mountains, respectively. The timing of watershed formation remains contentious, which hinders a comprehensive understanding of the geomorphic evolution of the Tibetan Plateau. The Qiangtang basin, where the CTWMs are situated, preserves critical geological records essential for deciphering landscape evolution. The age distributions of new detrital zircon U–Pb data from the Middle and Upper Jurassic sandstones in the northern Qiangtang sub‐basin are consistent with a published data set, with age clusters at 200–300, 500–700, 800–1000, 1800–2000 and 2400–2600 Ma. Qualitative provenance analysis identifies the major source rocks as the Palaeozoic and Upper Triassic strata in the CTWMs, as well as the Triassic turbidites in the Hoh Xil‐Songpan Ganze terrane (HSG), which bound the northern Qiangtang sub‐basin to the south and north, respectively. Minor contributions come from Late Triassic intrusive and volcanic rocks, as well as Jurassic granitoids. The abundant detrital zircon data from the Qiangtang basin offers an opportunity to investigate the formation of the CTWMs through a quantified interpretation of the source‐to‐sink system. The combination of inverse and forward modelling of large detrital data sets facilitates the creation of provenance maps and avoids laborious descriptions of individual age modes. Integrated with sandstone petrographic analysis and paleocurrent data, the provenance of the Jurassic sediments can be quantitatively constrained. The CTWMs within the Qiangtang basin consistently served as significant sources throughout the Jurassic, while younger zircon grains were contributed by local sources, including the Triassic and Jurassic magmatic rocks. The proportion of the HSG source in the north increased throughout the basin in the Middle Jurassic but decreased dramatically in the southern Qiangtang sub‐basin during the Late Jurassic. We interpret that the embryonic stage of the CTWMs, which did not fully prevent sediment transport from the HSG to the southern Qiangtang sub‐basin, persisted from the Early to Middle Jurassic. The formation of a well‐defined watershed occurred in central Tibet in the Late Jurassic, probably triggered by the trench‐parallel mid‐ocean ridge subduction of the Bangong‐Nujing oceanic lithosphere.

The analytical methods and procedures for the samples of this work (Text S1); zircon U-Pb dating results for volcanic rocks in the Duoma-Eyacuo area (Table S1); apatite fission-track results of the analytical samples (Table S2).

Understanding the geodynamics of the Tethys requires solid constraints on the evolution of the Tethyan Ocean. However, the exact closure time of the Longmu Co-Shuanghu Paleo-Tethyan Ocean remains poorly defined. To address this issue, we report a combined paleomagnetic, rock magnetic, and petrographic study of the Middle Triassic (similar to 240 Ma) volcanic-sedimentary sequence of the southern Qiangtang Terrane. Magnetite, along with minor amounts of pyrrhotite and hematite, are the magnetic carriers in the limestone, whereas magnetite and titanomagnetite constitute the principal magnetic carriers in the volcanic rocks. After tilt correction, the analysis of characteristic remanent magnetizations (ChRMs) from 18 sites yielded a mean direction of Ds = 55.4 degrees, Is = 36.2 degrees, alpha 95s = 6.4 degrees, and k = 29.9. The volcanic rock sites effectively averaged out the paleomagnetic secular variation, and the overall ChRMs passed the fold test. The determined paleomagnetic pole at 39.4 degrees N, 175.6 degrees E, with A95 = 5.7 degrees, indicates a paleolatitude of similar to 20.1 +/- 5.7 degrees N. A comparison of paleolatitudes between the northern and southern Qiangtang terranes reveals that the Longmu Co-Shuanghu Paleo-Tethyan Ocean was initially closed before or during the Middle Triassic. Available geological observations, including magmatic, metamorphic, and sedimentological records from the northern and southern Qiangtang terranes and the suture zone indicate a closure time ranging from late Middle Triassic to early Late Triassic. Thus, the combined geological records and paleomagnetic results suggest that the LongmuCo-Shuanghu Paleo-Tethyan Ocean was initially closed in the late Middle Triassic.

M & eacute;lange complexes and continental marginal deposits along suture zones can provide crucial insights into the subduction-accretion processes of oceanic lithosphere and continent-continent collisions. Herein, moderately to well-preserved Late Jurassic-Early Cretaceous and late Paleocene radiolarian assemblages, including 86 species within 52 genera, were identified in the Jiangmuna m & eacute;lange and the adjacent Tethyan Himalayan sedimentary strata along the western YarlungTsangpo suture zone, southern Tibet. Reconstruction of the ocean plate stratigraphy revealed that the Jiangmuna m & eacute;lange represents the products of fragmentation and mixing of Early Jurassic-Late Cretaceous ocean plate materials originally accumulated in different portions of the central Neo-Tethyan domain. The bottom-up lithological transition and the southward-younger seamount system indicate that the Neo-Tethyan oceanic lithosphere was subducted northward beneath the Zhongba microterrane, and then the Jiangmuna m & eacute;lange was accreted one unit after another along the southern margin of the Zhongba microterrane during the Late Cretaceous. The adjacent Tethyan Himalayan sedimentary strata were originally deposited in a continental slope-basin environment along the northern margin of the Indian plate since the Middle Jurassic. The occurrence of Selandian-Thanetian radiolarian assemblages implies that deep-water sedimentation persisted along the northern margin of the Indian plate until at least the late Paleocene. Our findings, combined with previously published data, indicate that the Neo-Tethys Ocean existed at least from the Early Jurassic to late Paleocene, and the NeoTethyan late-stage evolution involved at least two subduction-accretion systems along the southern margins of the Lhasa block and the Zhongba microterrane, respectively, prior to the two-stage India-Eurasia collision.

Oolitic ironstones in Lower (Toarcian) and Middle (Bajocian) Jurassic strata of the Indus Basin, Pakistan, were deposited in the eastern part of Tethys and are similar to those from India. Both units are represented by shallow-marine iron ooidal-siliciclastic wacke-packstone carbonates with sedimentary structures including ripple marks, cross lamination and trace fossils. Both the Toarcian and Bajocian iron ooids are mainly composed of goethite, the Toarcian ones have a higher Fe content than those in the Bajocian but the older unit has fewer silicate grains and lower contents of Si, Al, K and Sr. Thin to thick carbonate laminae occur between the Fe-rich laminae in the Bajocian iron ooids. The iron ooids in the Toarcian unit are related to phases of relative sea-level fall and represent deposition in a nearshore lagoonal setting whereas the Bajocian unit was deposited in a relatively broad spectrum of environments. The Fe itself was sourced from weathering of ferruginous soils and higher contents of K, Na, Ti and Ti/Al indicate a continental source. The cortical growth of the iron ooids in the Toarcian unit mainly took place under oxic conditions whereas conditions were more oxic to suboxic and anoxic in the Bajocian unit. The occurrence of spastoliths indicates the former presence of berthierine and the alternation of Fe-rich and carbonate-rich laminae within the Bajocian iron ooids suggests frequent burial and reworking of ooids in the near subsurface sub-oxic to anoxic environment. The subsequent exposure to oxic conditions on the seafloor likely altered the berthierine to goethite, which is stable in oxidizing conditions.

Paleoenvironmental reconstruction plays a pivotal role in providing insights into the uplift history of the Xizang Plateau during the Cenozoic. The Nima Basin, situated in the central Xizang Plateau, is crucial for studying the tectonic and geomorphic evolution of this region. The clastic composition and geochemical characteristics of the Niubao Formation hold considerable potential for unravelling the geological history and reconstructing depositional environments of central Xizang in the early Cenozoic. In this study, we present detailed geochemical characteristics to determine their provenance, paleoenvironmental conditions, and tectonic origins. The index of compositional variability (ICV > 1) of mudstones indicates that low compositional maturity sediments underwent weak sedimentary recycling. The chemical index of alteration (CIA: 59.8–72.9) reveals that parental rocks experienced a moderate chemical weathering degree. The paleoclimate indicators of the mudstones suggest an oxidizing and arid depositional environment, with a mean annual temperature (MAT) of 11.64°C ± 4.19°C. The geochemical evidence also demonstrates that the mudstones were derived from mixed felsic and intermediate igneous rocks that formed in a dominantly continental island arc tectonic setting. Similarities in the geochemical characteristics among the Niubao Formation and surrounding igneous rocks indicate that a continental-scale drainage system once drained westward in central Xizang. It is concluded that the central plateau experienced a cooler and drier climate coinciding with the presence of a large-scale drainage system during the late Eocene.

Deciphering the subduction dynamics of the Indian continental lithospheric mantle beneath the Tibetan Plateau after the India-Asia continental collision is pivotal for understanding continental convergence mechanisms and post-collisional magmatism. As sensitive probes of mantle metasomatism and slab dynamics, mantle-derived lamprophyres provide critical insights into the nature of the lithospheric mantle and the underlying geodynamics. However, the process of the spatiotemporal evolution of the Indian slab tearing during the postcollisional stage remains poorly constrained. Here, we present geochronology, geochemical and Sr-Nb-Pb isotopic analyses on lamprophyre dykes from the Xuena area in the southern Lhasa terrane to reveal the petrogenesis and geodynamic setting. The studied lamprophyres are characterized by phenocrysts of biotite and clinopyroxene set in a groundmass dominated by feldspar. LA-ICP-MS zircon U-Pb dating indicates emplacement of the lamprophyre dykes at 10.8 +/- 0.2 Ma. These lamprophyres exhibit high K2O (5.47-8.13 wt%) contents and moderate MgO (5.31-7.13 wt%) with shoshonitic and metaluminous signatures. They are enriched in large ion lithophile elements (LILEs), depleted in high field strength elements (HFSEs), and have a high abundance of rare earth elements (FREE = 672-984 ppm) with fractionated REE patterns ((La/Yb)N = 37-61). The lamprophyres are characterized by radiogenic initial 87Sr/86Sr ratios (0.711420-0.713660), unradiogenic epsilon Nd(t) values (-12.80 to-12.00), and radiogenic Pb isotopic signatures (206Pb/204Pb = 18.73-18.76, 207Pb/204Pb = 15.76-15.77, 208Pb/204Pb = 39.50-39.56). Geochemical characteristics indicate that the lamprophyres originated from low-degree partial melting of a phlogopite-bearing garnet lherzolite source. This source lies within the enriched Indian lithospheric mantle that has been metasomatized by subducted slab-derived fluids. The release of these fluids occurred during the subduction of the Indian continental lithosphere beneath southern Tibet. The primary geodynamic mechanism responsible for generating the lamprophyric magmas is the heat input from asthenospheric upwelling. It was induced by the tearing of the Indian continental slab, which triggered partial melting of the metasomatized Indian lithospheric mantle source. The Late Miocene lamprophyre dykes in Xuena and a series of lamprophyres in the southern Lhasa terrane and Himalayas show consistency in the spatiotemporal distribution and geochemical characteristics, which potentially indicates that the Indian continental slab had torn to the southernmost margin of southern Tibet by the Late Miocene. The findings provide new perspectives for unravelling the deep dynamic processes of the Indian continental slab.

Geochemical methods are the most widely used techniques for tracing the provenance of loess. However, the geochemical composition of loess can be influenced by particle size effect (PSE), potentially impacting the accuracy and reliability of provenance tracing. To date, no systematic and quantitative assessment has been conducted to evaluate the PSE on the geochemical indicators of loess. Using loess samples from northern and southern China, we conducted a detailed investigation of major, trace, and rare earth elements (REEs), as well as Sr‒Nd isotopes, across six particle size fractions to quantitatively assess the impact of particle size on loess geochemistry. The results show that most elements in loess are significantly affected by the PSE, which is driven by several mechanisms. Mineral sorting primarily affects the PSE of major elements, while chemical weathering enhances the PSE of both major and trace elements, and colloidal adsorption mainly contributes to the PSE of trace elements and REEs, particularly heavy rare earth elements. We recommend selecting a size window of 10–50 μm (or 16–32 μm) for loess provenance tracing, rather than using fractions smaller than 20 μm. Furthermore, we identified nine elemental indicators—Zr/Hf, δEu, La/Sm, Sm/Nd, La/Nd, Y/Ho, Y/Er, Ho/Er, and Yb/Lu—that are independent of particle size. The major elemental ratio K 2 O/Al 2 O 3 can serve as a valid tracer only in arid and semi‐arid regions. For Sr‒Nd isotopes, 143 Nd/ 144 Nd is two orders of magnitude less affected by the PSE than 87 Sr/ 86 Sr and should be prioritized for provenance studies of loess.