The Paleo-Tethyan arc belt is of enormous scale, but hosts few porphyry Cu-Au deposits. Previous studies suggest that the arc magmas are overall reduced and infertile during Permian-early Triassic. Nevertheless, the tectonic evolution and Cu-Au fertility of early-stage (Late Devonian to Carboniferous) Paleo-Tethyan arc magmatism remain poorly understood. Here, we address these issues by investigating the petrogenesis and fertility of a newly identified Late Devonian granodiorite intrusion (Gucaicun, 362.4 +/- 2.3 Ma) in eastern Tibet. The granodiorite is calc-alkaline to high-K calc-alkaline in composition, and shows enrichment in LILEs but depletion in HFSEs, which are diagnostic of arc magmatism. Whole-rock trace elemental characteristics (e.g., Rb vs. Yb + Nb, Th/Yb vs. Nb/Yb) indicate that this intrusion was formed in a continental arc setting. Depleted whole-rock Sr-Nd and zircon Hf isotopes [(87Sr/86Sr)i = 0.704368-0.704427; epsilon Nd(t) = 3.9-4.4; epsilon Hf(t) = 7.0-13.0] further demonstrate its derivation from subduction-modified asthenosphere mantle wedge. Integrated with coeval arc rocks reported in northern Tibet, this study suggests the possible existence of an early-stage, Late Devonian to Carboniferous Paleo-Tethyan arc belt across the northeastern Tibet, providing important evidence for the early evolution of the Paleo-Tethys Ocean. The intrusion has high magmatic oxygen fugacity (zircon Delta FMQ = 0.44-1.45, mean = 0.95 +/- 0.27) and elevated whole-rock Pd and Pt contents, which are comparable to global Au-rich porphyry Cu deposits. These features are distinct from the reduced and infertile magmas during the middle-late Permian, suggesting significant temporal heterogeneity in porphyry Cu-Au potential of Paleo-Tethyan arc magmas.

The Sanjiang Tethyan orogenic belt, a globally representative composite multi-island arc-basin system, has been a focus of ongoing debate regarding the coupling relationship between the Proto- and Paleo-Tethyan tectonic evolution and metallogenic processes. This study systematically synthesizes regional geological, geochronological, and metallogenic data to characterize the distinct tectonic units within the Sanjiang Composite Orogenic System. A tectono-metallogenic coupling model is established by integrating the spatiotemporal distribution of ophiolites, high-pressure metamorphic rocks, and representative ore deposits. The Changning-Menglian suture zone preserves a complete record of the oceanic-basin evolution from subduction to final closure, including Early Paleozoic Lancang Group accretionary complexes, Ordovician-Silurian ophiolites, Early Paleozoic high-Mg adakites, Devonian-Carboniferous oceanic island basalts, and Middle-Late Triassic eclogites. Our results demonstrate a strong genetic correlation between regional metallogenesis and tectonic settings: extensional settings control Sedex-type Pb-Zn deposits, subduction systems dominate VMS-type Cu-Pb-Zn mineralization, collisional stages develop porphyry-skarn Cu-Mo deposits, while post-collisional extension triggers Sn-W and epithermal Pb-Zn mineralization. Innovatively, this study proposes a four-stage tectonic-metallogenic evolution model for the Proto- and Paleo-Tethyan Ocean: (1) Early Paleozoic passive margin extension (Sedex-type Pb-Zn mineralization); (2) Middle Ordovician to Silurian subduction (VMS/BIF-type mineralization); (3) Late Paleozoic development of a multi-island arc-basin system (large-scale VMS-type mineralization); and (4) Middle-Late Triassic collisional orogeny (eclogite deep subduction, porphyry-skarn Cu-Mo, and Sn-W mineralization). These findings provide new insights into the multi-stage dynamic processes of Proto- and Paleo-Tethyan evolution and clarify the controlling mechanisms of diverse tectonic settings (rift → subduction → collision → intracontinental extension) on metallogenic systems.

The Milin ultramafic-mafic intrusive rocks, exposed in the southeastern segment of the Gangdese batholith within the southern Lhasa subterrane, provide critical insights into the Late Cretaceous tectonic-magmatic evolution of southern Tibet. New zircon U-Pb geochronology yields a crystallization age of ca. 85 Ma, indicating that the mantle-derived magmatism was synchronous with the peak of the regional magmatic flare-up. Petrological and geochemical evidence reveals that these rocks are hydrous cumulates that were primarily formed via fractional crystallization and accumulation of olivine and clinopyroxene. They are characterized by high MgO contents and Mg# values, light rare earth element (LREE) enrichment, heavy rare earth element (HREE) depletion, pronounced negative Nb anomalies, and positive Ta anomalies. Further, their highly positive zircon epsilon Hf(t) values (+10.5 to +14.4) and specific trace element signatures (e.g., low Nb/U and Ce/Pb ratios) indicate that the magmas were derived from depleted asthenospheric mantle metasomatized by subductionrelated fluids. Based on all of the data, we attribute the formation of the Milin intrusions to the roll-back of the subducted Neo-Tethyan oceanic slab. This geodynamic process triggered asthenospheric upwelling and decompression melting of the fluid-modified mantle reservoir, producing hydrous high-Mg parental magmas that drove Late Cretaceous crustal growth in the southern Lhasa subterrane.

The Jiaduoling area is located in the northern segment of the Southwest Sanjiang Metallogenic Belt, a region characterized by complex geological structures and abundant mineral resources. This study systematically identifies the spatial correlation between subsurface magnetic bodies and tectonic structures by utilizing 1:50,000 high-precision aeromagnetic data. Advanced processing techniques—including upward continuation, vertical derivatives, total gradient modulus, and Euler deconvolution—were integrated to refine the structural framework and clarify the mechanisms of fault-controlled mineralization. The results indicate that the aeromagnetic anomaly pattern is predominantly governed by NW-trending faults. Specifically, the deep-seated major fault F1 (with a calculated depth exceeding 3 km) served as the primary migration channel for ore-forming fluids, while secondary faults created localized ore-hosting spaces. Physical property analysis reveals a significant magnetic contrast, where Mesozoic intermediate-acid magmatic rocks act as the essential source for mineralization, providing both material and thermal energy for the formation of porphyrite-type iron deposits. Based on these findings, a three-dimensional “aeromagnetic anomaly-structural framework-mineralization” correlation model was established. Finally, two high-potential metallogenic prospective zones (P1 and P2) were delineated, providing precise geophysical evidence and strategic guidance for regional mineral exploration and the targeting of concealed ore bodies.

The timescales for the duration and final closure of the Paleo-Tethys Ocean (PTO) remain controversial. To address these issues, this study reports the geochronological and geochemical data of two newly identified retrograded eclogites in the southeastern Tibetan Plateau. These eclogites outcropped in the Genhen and Mangna regions within the Changning-Menglian suture that represents the extinct site of the PTO. Geochemically, the protoliths of the Genhen and Mangna samples are arc-related and oceanic crust-related mafic rocks, respectively. Zircon cores that exhibit oscillatory zoning, high Th/U ratios, and enriched heavy rare earth element (HREE) patterns yield UPb ages of 250 +/- 1 Ma and 429 +/- 3 Ma, which are interpreted as the formation ages of their protoliths. Combined with other early Paleozoic magmatic and metamorphic records in this suture, we propose that the PTO may have existed for over 200 Myr in the southeastern Tibetan Plateau. By contrast, zircon rims characterized by low Th/U ratios and flat HREE patterns yield UPb ages of 230 +/- 4 Ma and 231 +/- 2 Ma, which are consistent with the Ar-40/Ar-39 plateau age (232.6 +/- 2.2 Ma) of phengites from the country-rock schist. In addition, given that phengite inclusions have been found in zircon rims, we propose that these eclogites with varying protolith ages simultaneously experienced retrograde metamorphism at similar to 230 Ma, which might be associated with slab break off and exhumation after continental collision. Our data reconstruct the timelines for the development of the PTO in the southeastern Tibetan Plateau, including its persistence from the early to late Paleozoic and final closure prior to the high-pressure metamorphism at similar to 230 Ma but not earlier than the youngest protolith ages (similar to 250 Ma) of retrograded eclogites. These approaches and results have general implications for understanding the tectonic evolution of the Paleo-Tethys Ocean.

Tectonic plate convergence is accommodated across the continental lithosphere via discrete lithospheric subduction or distributed shortening and thickening. These end-member deformation modes control intra-plate mountain building, but their selection mechanism remains unclear. The variable composition of the continental crust and lithospheric mantle, which impacts its density and rheology, can be inferred by the distribution of magnetic-indicated crustal iron. Here we demonstrate that vertically coherent pure-shear shortening dominated the active Tian Shan orogen, central Asia, based on high-resolution aeromagnetic imaging and geophysical-geodetic observations. Integrating these findings with thermomechanical collisional models reveals that the mode of intracontinental deformation depends on contrasts in lower crust composition and mantle lithosphere depletion between the converging continents and central orogenic region. Distributed shortening prevails when the converging continents have a more iron-enriched mafic crust and iron-depleted mantle lithosphere when compared to the intervening orogenic region. Conversely, continental subduction occurs without such lithospheric contrasts. This result explains how the Tian Shan orogen formed via distributed lithospheric thickening without continental subduction or underthrusting. Our interpretations imply that iron distribution in the crust correlates with lithospheric compositional, density, and rheological structure, which impacts the preservation and destruction of Earth's continents, including long-lived cratons, during intracontinental orogeny.

The evolution of continents is shaped by the growth and destruction of long-lived cratons, which serve as their stable cores. Processes for craton destruction are controversial because most invoked mechanisms occur frequently throughout Earth history, making the preservation of cratons for billions of years problematic. Here, we address this issue by presenting a crustal-scale analytical signal-amplitude model obtained from high-resolution airborne and shipborne magnetic data across cratons within East Asia. Magmatic, magnetic, and basin-history constraints show that the eastern North China craton experienced focused weakening, thickening, and catastrophic destruction of its mantle lithosphere due to a unique combination of circum-craton subduction and subsequent collision since the Paleozoic. By contrast, the adjacent South China craton was not impacted in this way, and thus, its mantle root was spared from destruction. The long-term survival of cratons may stem from the infrequent occurrence of sustained circum-cratonic subduction or collisional processes capable of destabilizing their lithospheric roots.

The Zhenghe-Dapu fault (ZDF), situated in the Cathaysia Block of South China, has played a major role in the tectono-magmatic and geothermal activities in the region since Mesozoic-Cenozoic. However, the regional topography restricts the availability of surface heat flow data, hindering lithospheric thermal structure studies. Therefore, we used a broadband and long-period magnetotelluric profile with 33 points across the Cathaysia Block and ZDF to obtain a 3-D electrical conductivity model. Tectonic zones, such as the Jiangshao fault and ZDF exhibit high-resistivity (>1000 Omega m) blocks, interpreted as remnants of the cratonic lithosphere; low-conductivity areas (<100 Omega m) indicate lithosphere modified by materials derived from the deep mantle. A high-conductivity body (<10 Omega m) in the lower crust (similar to 20-30 km) beneath the ZDF coincides with spatial position of low magnetic anomalies, high gravity, and low S-wave velocity. Moho depth (similar to 34 km) is significantly greater than that in the adjacent areas (similar to 28-32 km). Integrated geophysical observations suggest that the high-conductivity body may represent mantle-derived melt fluids ascending along faults, leading to the partial melting of lower crustal rocks. Mantle intrusion led to the thickening of the lower crust, that previously underwent regional thinning, ultimately resulting in the formation of a substantial amount of Mesozoic granite bodies, the radiogenic heat of which constitutes a major heat source. Since the Cenozoic, asthenospheric thermal material upwelling, magmatic underplating, and volcanic activity have provided heat to the upper crust. The radiogenic heat from the Mesozoic granites and Cenozoic magmatic-hydrothermal activities together contributed to the regional thermal anomaly, as supported by our resistivity model.

Observations and interpreted mechanisms for the reworking of Precambrian cratons and accretionary orogens have significant relevance in understanding the history and evolution of continental lithosphere. Here we investigate the Precambrian basement and lithospheric architecture of the western North China craton (NCC) through the integration of multiple geophysical data sets, including density structure derived from 2D velocity-constrained gravity-focused inversion, along with newly-compiled aeromagnetic, magnetotelluric (MT) and shear-wave velocity data. We present five multi-geophysical sections illustrating the lithospheric structure along compiled MT profiles in western NCC. The mantle lithosphere of the central-western Alxa block and central-southern Ordos block is primarily characterized by high velocity, low-moderate density and high resistivity. This contrasts with the mantle lithosphere on or near the Inner Mongolia Suture Zone (IMSZ), where an apparent low resistivity zone with anomalous density marks the Paleoproterozoic suture between the Yinshan block and the Ordos block. Our results demonstrate the Alxa block's preservation of an Archean-Paleoproterozoic metamorphic basement, linking it as the westward extension of the Yinshan block and an integral part of the Precambrian NCC. We propose that the marked lithospheric geophysical anomalies of the IMSZ mainly resulted from subduction processes related to the Paleo-Asian and Paleo-Pacific oceans. Our findings suggest the Precambrian cratonic accretionary orogens are more vulnerable to modification than adjacent Archean nuclei during later tectonic events. Therefore, cratonic accretionary orogens may be important for processes of craton destruction, continental breakup and lithospheric healing.

The evaluation of geological suitability for urban underground space (UUS) development is an indispensable prerequisite for its optimal utilization. As the actual carrier of underground facilities, the evaluation of rock mass quality plays a crucial role in assessing geological suitability. However, it is notable that the evaluation of rock mass quality has regrettably remained somewhat marginalized within the broader framework of the geological suitability assessment in recent years. The selection of pertinent indicators for the evaluation of rock mass quality inherently presents an appreciable degree of subjectivity. Predominantly subjective evaluation methods continue to dominate the field, while the application of objective algorithms, such as unsupervised clustering, remains in its nascent stage. Furthermore, there is a lack of comprehensive investigations into distinct combinations of attributes. This limitation confines the broader applicability of the evaluation outcomes in the context of urban underground space. Within this study, we meticulously amassed rock core test data from over 40 boreholes of engineering geological significance within the urban planning ambit of Guang'An City. Utilizing the K-means unsupervised clustering algorithm and the Principal Component Analysis (PCA) algorithm. We successfully conducted an unsupervised clustering procedure with nine distinct physical and mechanical attributes. This yielded an aggregation into five discernible clusters. Building upon the derived clustering outcomes, a stratification of rock mass quality was effectuated into three distinct tiers: Level 1 (characterized by pure sandstone), Level 2 (primarily dominated by sandstone), and Level 3 (denoting fair conditions predominantly influenced by mudstone). This structured stratification facilitates a relatively objective and comprehensive evaluation of rock mass quality within the context of the red-bed hilly terrain. In the course of this analytical trajectory, we conducted a dissection of the clustering efficacy. For strongly correlated attributes, we propose a preliminary dimensionality reduction procedure prior to the clustering endeavor. Moreover, we recommend intervals of 10 m for the stratified evaluation in red bed hilly urban terrains.

We report isolated postcranial materials newly excavated from the Middle Jurassic Dongdaqiao Formation in Chaya County, Qamdo City, eastern Tibet. The specimens are assignable to Eusauropoda based on the following combination of characters: huge size of caudal vertebrae and humeral shaft, weakly developed amphicoelous caudal centrum, femoral distal ends with two condyles and a shallow intercondylar groove, and rod-like transverse process of the anterior caudal vertebra with its base not extending to the neural arch. Due to the fragmentary nature of the specimens, we refrain from assigning them to lower taxonomic levels or new species of sauropod until more complete materials are excavated from Qamdo. Nevertheless, the new materials from Qamdo demonstrate that some gigantic sauropods migrated to eastern Tibet during the Middle Jurassic and were more widely distributed than previously known.

Being the most commonly dated accessory mineral, the geochemical makeup of zircon has increasingly been recognized as a promising indicator of the parent magma composition, providing a means to reconstruct the paleo-crustal thickness of orogenic belts where whole-rock records are limited. However, the robustness of zircon approaches in paleo-crustal thickness reconstruction remains controversial. Here, we report on U-Pb age, trace element and Hf isotope data for zircon in sedimentary rocks of central Tibet, aiming to reconstruct the central Tibetan paleo-crustal thickness evolution from Meso-Tethyan subduction to the India-Asia collision, and test the results by comparing against geological evidence. The consistent variations of different pressure-sensitive geochemical proxies over time, e.g., (La/Yb)N, (Sm/Yb)N, MREE/HREE, Eu anomaly, and Y values, indicate that pressure is the first-order control on zircon compositional changes. Using southern Tibet as a reference and comparing the results from various geochemical proxies, we find that zircon Eu geochemical proxy yields relatively reasonable estimates of paleo-crustal thickness for this orogen, which is thereby employed to explore the evolution of paleo-crustal thickness in central Tibet. A history of multi-stage thickening crust separated by episodes of thinning for central Tibet is revealed by zircon multi-proxy approach, and supported by multiple lines of independent evidence, including whole-rock geochemical proxies, structural geology, low-temperature thermochronology, and paleo-altimetry. We propose that a thick crust similar to the current one was likely formed in central Tibet by the Late Eocene (similar to 40-35 Ma), predominantly due to crustal shortening as a consequence of the India-Asia collision. Our study strengthens the applicability of zircon petrochronologic data in delineating the paleo-crustal thickness evolution of specific regions when supported by rigorous and comprehensive regional geological evidence.

The post-collisional evolution of the Tibetan lithosphere is of paramount significance to our understanding of collisional orogeny. It is generally postulated that the Lhasa lithospheric mantle was horizontally shortened and thickened coherently with the overlying crust to form a physical barrier, preventing Indian subduction beneath Tibet until the thickened mantle root was foundered during the Miocene. This study first identifies post-collisional oceanic-island basalt (OIB)-type magmatism in the Lhasa Block (LB), as attested by zircon U-Pb age (ca. 58 Ma) and geochemistry—positive Nb-Ta anomalies, high La/Yb, and depleted bulk-rock Sr-Nd and zircon Hf isotopes, of diabase in the northern (inboard relative to Indus Suture) part of this block. Coupled with extensive early Paleogene arc-type magmatism in the southern-central LB and thermodynamic modeling, we suggest that these diabases were formed by partially molten upwelling asthenosphere near the base of continental crust, where much of the underlying lithospheric mantle had been removed due to Neo-Tethyan slab rollback and lithospheric delamination. Compared to OIB-type magmatism worldwide, the diabases investigated here were emplaced peculiarly in a region where the continental crust was under horizontal compression and shortening by coeval thrusting. Our study thus implies a decoupled deformation between the crust and mantle of the LB during the early Indian-Asian collision.

The super-chondritic Mo isotopic composition of the continental crust has been attributed to contributions from subducted oceanic slabs and/or sediments, which introduce isotopically light Mo to the mantle. It has been hypothesized that dehydrated oceanic slabs subduct into the deep mantle and contribute to the genesis of ocean island basalts (OIBs). However, OIBs have similar average delta Mo-98/95 values (-0.22 parts per thousand +/- 0.04 parts per thousand ; 2SE; n = 87) to the depleted mantle. Subducted oceanic sediments may create a light-delta Mo-98/95 reservoir in the subcontinental lithospheric mantle, but this has not been investigated in detail. Understanding the Mo isotopic systematics of the continental crust and mantle requires an understanding of the Mo isotopic composition of lithospheric mantle-derived volcanic rocks. The litho-sphere in the Tibetan region has experienced multiple stages of oceanic subduction and is thus ideal for studying magmas derived from sediment-modified lithospheric mantle. Mafic ultrapotassic volcanic rocks (UPVRs) from the Sailipu area on the southern Tibetan Plateau have high Mg# values (67.1-72.5) and enriched Sr-Nd isotopic compositions and are primitive magmas derived from the lithospheric mantle. These rocks have higher Ce/Mo ratios (225-422) and lighter delta Mo-98/95 values (-0.45 parts per thousand to-0.13 parts per thousand) than the depleted mantle, mid-ocean ridge basalts (MORBs), and OIBs, as well as high epsilon(Hf)(t) values at given epsilon(Nd)(t) values compared with the terrestrial array (delta epsilon(Hf) = 4.59-5.73). The involvement of Ca-poor pelagic sediments rather than the lower continental crust and hydrated oceanic slab best accounts for the high Ce/Mo ratios and light delta Mo-98/95 values of the studied rocks. The Sailipu UPVRs also have higher Nb/Ta (18.9-20.8) and Th/La (2.6-3.4) ratios than arc-related igneous rocks and MORBs, suggesting that their source was phlogopite-bearing lithospheric mantle with a metasomatic vein component (rutile + monazite +/- lawsonite). We propose a two-stage geodynamic process to explain the formation of the Sailipu UPVRs: (1) a metasomatic vein component with high Th/La and Ce/Mo ratios formed in the litho -spheric mantle during multiple stages of oceanic subduction; (2) high mantle temperatures related to convective thinning of the lithosphere resulted in melting of the vein component and the ambient man-tle, which produced hybrid melts of various mantle domains during the post-orogenic stage. The Sailipu UPVRs have enriched Sr-Nd isotopic compositions and high Th/La and Ce/Mo ratios, similar to lamproites that are widespread in the Tethyan orogenic realm from the Mediterranean to the southern Tibetan Plateau. Given that UPVRs with light delta Mo-98/95 values have also been identified in the Western Alps, we propose that the isotopically light Mo component is widespread in Tethyan lithospheric mantle. This iso-topically light Mo in the lithospheric mantle may be a complementary end-member to the isotopically heavier continental crust. The recycling of subducted oceanic sediments has a key role in the deep recy-cling of Mo.(c) 2022 Elsevier Ltd. All rights reserved.

To date, the evolutionary history of the Proto‐Tethys Ocean that separated the Gondwana and Laurasia continents remains ambiguous. The Changning‐Menglian Suture Zone assumingly represents the Proto‐ and Palaeo‐Tethys suture in the Sanjiang area (the Yunnan Province, southwestern China). The Palaeozoic Proto‐Tethys Ocean in the Manxin area in the southmost Changning‐Menglian Suture Zone is widely recognized, but the timing and formation mechanism of the Manxin ophiolitic mélange are poorly understood. In this study, we present petrographical, geochronological and geochemical data of the Manxin ophiolitic mélange situated in the Changning‐Menglian Suture Zone. We found that this ophiolitic mélange is composed of pillow basalt, metamorphic gabbro, diabase dike, and altered peridotite. The mafic rocks could be divided into two groups based on geochemical characteristics: (1) Mid‐ocean ridge basalt (MORB) [formed at 446.0 ± 3.2 Ma and exhibiting depleted light rare earth element (LREE) patterns and high Ɛ Nd (t) (+5.7 to +8.4)] Trace element and isotope analyses indicated that the MORB was derived from a spinel‐facies depleted mantle. (2) Ocean island basalt (OIB) [crystallized at 460.2 ± 6.0 Ma]. Ɛ Nd (t) (+5.7) and significant enrichments in large‐ion lithophile element (LILE) and light rare earth element (LREE) were identified, while the trace element and isotope systematics suggested that the OIB rocks originated from partial melting of the garnet‐spinel lherzolite mantle. Overall, we clearly constrained the timing and nature of the Manxin ophiolitic mélange using the proposed data, thus further supporting the notion that the Manxin ophiolites represent remnants of the Proto‐Tethys Ocean.

Unsubducted, and trapped or accreted oceanic crust contributes greatly to continental growth. The Alxa tectonic belt (ATB) is located at the critical intersection of the Central Asian Orogenic Belt (CAOB) and the North China Craton. However, little attention has been paid to the influence of the evolution of the Beidashan-Langshan arcuate tectonic belt in the ATB on the closure of the Paleo-Asian Ocean, the formation of the CAOB, and the growth of continental crust. Here we report new integrated airborne gravity and magnetic surveys in the ATB that image a high-amplitude magnetic anomaly zone distributed across the Quagan Qulu ophiolite belt. The three-dimensional magnetic structure inversion reveals that the Quagan Qulu magnetic anomaly zone consists of mid-lower crustal high-value magnetic susceptibility. Gravitymagnetic forward modeling reveals that the Quagan Qulu magnetic anomaly zone may have been generated by a crustal mafic pluton characterized by high magnetism and density, approximately same to the magnetic susceptibility and density of the exposed Late Paleozoic gabbros measured in the field, which are consistent with those of the Yueyashan-Xichangjing ophiolite belt in the Beishan orogenic belt adjacent to the ATB. We argue that the mafic pluton beneath the Quagan Qulu zone may be the trapped oceanic crust derived from the Late Paleozoic-Triassic Paleo-Asian Ocean (i.e., the Quagan Qulu Ocean). In conjunction with the integrated petrologic, chronologic and geochemical observations, we argue that the Beidashan-Langshan arcuate tectonic belt dominated the differential subduction of the Paleo-Asian Ocean and finally trapped partial Quagan Qulu oceanic crust. Therefore, we propose that, in addition to oroclines, the irregular continental margins could alternatively provide tectonic space for trapping oceanic crust, contributing to the lateral growth of the continental crust and serving as an important means of continental accretion in the CAOB.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

As one of the important Paleo-Tethys suture zones in eastern Tibet, the Jinshajiang orogenic belt is of great significance to study the tectonic evolution of the main suture zone of Paleo-Tethys. In this paper, eclogites developed in the Jinshajiang suture zone in Gonjo area, eastern Tibet, are selected as specific research objects, and petrological, geochemical and Ar-Ar geochronological analyses are carried out. The major element data of the whole rock reveals that the eclogite samples have the characteristics of picritic basalt-basalt and belong to the oceanic low potassium tholeiites. The results of rare earth elements and trace elements of the samples show that the protoliths of eclogites have characteristics similar to oceanic island basalt (OIB) or normal mid ocean ridge basalt (N-MORB). Muscovite (phengite) from two eclogite samples yield the Ar-Ar plateau ages of 247 ± 2 Ma and 248 ± 2 Ma respectively, representing the peak metamorphic age of eclogite facies and the timing of complete closure of the Jinshajiang Paleo-Tethys Ocean. Muscovite and biotite selected from the hosting rocks of eclogite yield the Ar-Ar plateau ages are 238 ± 2 Ma and 225 ± 2 Ma respectively, reflecting the exhumation age of eclogites and their hosting rocks. Combined with the zircon U-Pb dating data (244 Ma) of eclogites obtained in previous work, it can be concluded that the Jinshajiang Paleo-Tethys ocean was completely closed and arc-continent collision was initiated at about 248–244 Ma (T21). Subsequently, due to the large-scale arc (continent)-collision orogeney between Deqin-Weixi continental margin arc and Zhongza block (T31–T32), the eclogites were rapidly uplifted to the shallow crust.

Jurassic strata are widely distributed in the eastern part of Tibet Autonomous Region, and have yielded many dinosaur bones. However, none of these specimens has been studied extensively, and some remain unprepared. Here we provide a detailed description of some new sauropod material, including several cervical vertebrae and a nearly complete scapula, recovered from the Middle Jurassic of Chaya County, East Tibet. The cervical vertebrae have short centra that bear ventral midline keels, as in many non-neosauropod sauropods such as Shunosaurus. Moreover, the cervical centra display deep lateral excavations, partitioned by a septum. The scapula has proximal and distal ends that are both expanded as in mamenchisaurids and neosauropods. However, relatively small body size and lack of fusion of neurocentral sutures in the cervical vertebrae suggest that the available material is from a juvenile, and the length of the cervical centra may have increased relative to the size of the rest of the skeleton in later ontogenetic stages. Phylogenetic analysis provides limited evidence that the new Tibetan sauropod specimen belongs to Eusauropoda, being more derived than Shunosaurus, but is basal to Mamenchisauridae. The new material provides important information on the morphological transition between Shunosaurus and mamenchisaurids, and extends the known biogeographic range of early-diverging sauropods in the Middle Jurassic of East Asia.