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We present a 3‐D crustal S‐wave velocity (Vs) model for eastern and northeastern Tibet utilizing ambient noise tomography. Our model reveals that crustal flow channels are absent in northeastern Tibet. In this region, the Kunlun Fault (KLF) significantly impacts mid‐lower crust low‐Vs anomalies. In addition, isolated low‐Vs anomalies beneath the Qilian orogeny are unrelated to the low‐Vs materials of the Tibetan Plateau. In the mid‐lower crust of the Songpan‐Ganzi terrane, its northeastern corner exhibits continuous low‐Vs anomalies, limited to areas south of the West Qinglin and west of 104° E. This suggests that a small‐scale northward viscous flow of crustal materials exists in the eastern KLF. However, two significant crustal flow channels (Vs ≤ 3.3 km/s) are observed in eastern Tibet. The east–west tectonic movements and the obstruction of the Sichuan Basin together facilitate the dispersion of crustal materials southward from eastern Tibet. [ABSTRACT FROM AUTHOR]

This paper aims to update our understanding of the carbon cycle in the Himalayas, the most intense collisional orogeny globally, by providing new insight into its impact on Cenozoic climate cooling through the use of isotopic variations in both organic and inorganic carbon and an isotopic mass balance model. Our results from 20 selected hot springs show that the relative contributions of dissolved carbon from the mantle, metamorphic decarbonization, aqueous dissolution, and soil organic matter are approximately 2%, 82%, 6%, and 10%, respectively. Approximately 87% ± 5% of CO2 generated in the deep crust precipitates as calcite, while approximately 5.5% ± 1% of this carbon is converted to biomass through microbial chemosynthesis at depths less than 2 km. Our random forests approach yielded a metamorphic carbon flux from the entire Himalayan orogenic belt of approximately 2.7 ∼ 4.5 × 1012 mol/yr. The minor CO2 released into the atmosphere (2.5 ∼ 4.2 × 1011 mol/yr) is comparable to the carbon consumption driven by Himalayan weathering. This paper provides new insights into deep carbon cycling, notably that approximately 93% of deeply sourced carbon is trapped in the shallow crust, rendering orogenic processes carbon neutral and possibly acting as one of the major triggers of long‐term climate cooling in the Cenozoic. Plain Language Summary: Large‐scale deep metamorphic decarbonization and CO2 release into the atmosphere during continental collision orogenesis worldwide have had significant impacts on Cenozoic global climate change. However, the carbon sources and sinks and the mechanisms underlying their impacts on climate change are not fully understood. This paper reports the chemistry of aqueous solutions, carbon isotopic compositions of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), and helium and carbon isotopic compositions of free gases from hot springs in southern Tibet. The carbon isotope fractionation model between gas and aqueous solutions revealed that the carbon released from depth underwent six different stages. Based on the random forests machine learning algorithm, we estimated the metamorphic carbon flux across the Himalayan orogenic belt. Furthermore, only a small fraction (7%) of deep carbon is eventually released into the atmosphere, and this volume is the same magnitude as the amount of carbon absorbed by silicate weathering on the Tibetan Plateau. This paper emphasizes that the carbon sequestration process in the upper crust may have resulted in nearly carbon‐neutral geological bodies in the Himalayan orogenic belt, thus playing a critical role in Cenozoic climate cooling. Key Points: Approximately 87% of deeply sourced carbon precipitates as calcite, while approximately 5.5% is sequestered as biomass in the shallow crustThe carbon flux across the Himalayan orogenic belt was estimated by the random forests approachCrustal thickening has attenuated long‐term deep carbon emissions from the Himalayas [ABSTRACT FROM AUTHOR]

Understanding lithospheric rheology is crucial in investigating tectonic evolution of intra‐continental tectonic boundary. Here, we use geodetic observations to infer lithospheric rheology across the northeastern Tibet based on a 2D viscoelastic model. Our findings reveal a lower‐crust viscosity of <1022 Pa·s underneath its margins, lower than those estimated underneath its vicinities. By comparing deformation patterns and lithospheric rheology here with those observed in the eastern Tibet, we propose that lateral variations in lower‐crust viscosity control deformation patterns and topographic gradients along the Tibet margins. The presence of low viscosity lower‐crust can lead to the development of contrasting topographic gradients and shape the plateau's geomorphology and deformation characteristics during outward growth of the Tibet. We here emphasize the subtle variations in the lower‐crust rheology between deforming blocks and the corresponding mountain ranges, which play an important role in orogeny along the intracontinental convergence boundary. Plain Language Summary: The Tibetan Plateau undergoes remarkable outward growth driven by the ongoing convergence between the Indian and Eurasian plates. Significant questions remain as to the mechanisms responsible for generating distinct topography and deformation patterns along the Tibet margins, particularly when it encounters surrounding rigid continental blocks. The presence of these blocks poses a unique challenge in understanding processes that shape the plateau's geomorphology and deformation characteristics. Here we use geodetic observations to infer the lithospheric rheology across the northeastern Tibet based on a 2D viscoelastic model. We show that the lower‐crust viscosity underneath the margin of northeastern Tibet is notably lower compared to those of underneath its surrounding areas. By comparing these findings with the distinct topography, deformation patterns, and lithospheric rheology observed across the eastern margin of Tibet, we propose that lateral variations in lower‐crust viscosity between active tectonic blocks control the formation of mountain range‐fronts. The weak lower‐crust underneath the mountain ranges exerts a significant influence on uplift dynamics, determining the location of the maximum surface uplift and topographic gradient. Key Points: We infer lithospheric rheology across the northeastern Tibet using geodetic observations based on a 2D viscoelastic modelThe interpretation of surface deformation patterns requires a low viscosity wedge underneath the margin of northeastern TibetThe maximum surface uplift is predicted where the lower‐crust viscosity is the lowest along the intra‐continental convergence boundary [ABSTRACT FROM AUTHOR]

[Display omitted] After two continents collide, plate convergence and orogenesis are sustained because subducted continental lithosphere continues pulling the surface plate. It remains controversial how, why, and when continental plate convergence and collision slow down and eventually cease. We use an unprecedented data coverage and present a regional-scale seismic tomographic image of the mantle structure beneath the Tibetan Plateau. In the mantle transition zone, we identify multiple high-velocity anomalies and interpret them as detached pieces of the Indian continental slab. Facilitated by internal heterogeneity of the continental lithosphere, piecewise slab detachments could reduce the slab pull force, resulting in the Miocene slowdown of the India-Eurasia convergence and coeval diachronous potassic volcanism in southern Tibet. We propose that slab detachment is a mechanism that eventually will lead to the end of the Indo-Eurasian continental collision and the Himalayan orogeny. [ABSTRACT FROM AUTHOR]

Post-collisional (ultra)potassic lamprophyre dykes are the key probes for understanding mantle metasomatism and reconstructing tectonic evolution. In this study, we present new petrological, geochronological, geochemical and zircon Lu-Hf isotopic data for lamprophyre dykes in the northern Qiangtang terrane (central Tibet), aiming to constrain their petrogenesis and geodynamic setting. The studied lamprophyres are minettes with phenocrysts of siderophyllite and phlogopite, which intrude into Triassic granite of 236.9 Ma. These lamprophyres yield zircon U-Pb ages of 39.7–40.9 Ma. They exhibit high contents of K2O (7.61–8.59 wt.%) and ultrapotassic features with high K2O/Na2O (11.43–14.38) ratios. They are characterized by increased values of Mg# (69.1 to 72.1) and high concentrations of compatible elements (e.g., Cr = 277–529 ppm, Ni = 232–322 ppm), which are diagnostic of mantle-derived primitive magma. The studied lamprophyres have a high abundance of rare earth elements (∑REE = 902–1061 ppm) with significantly fractionated REE patterns ((La/Yb)N = 66.3–100.6), and they are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field strength elements (HFSE) (e.g., Nb, Ta and Ti) and heavy rare earth elements (HREE) with enriched zircon Hf isotopes (εHf(t) from −6.40 to 3.80). This indicates their derivation from an enriched mantle source which was metasomatized by subduction-related fluids and sediment-derived melts. A petrogenetic study suggests that the lamprophyres were generated by the partial melting of a phlogopite-bearing lherzolite within the garnet stability field. We propose that the Cenozoic ultrapotassic mafic rocks in the central Tibetan Plateau originated in the lithospheric mantle metasomatized by the subduction-related components, and are the magmatic response to the detachment of the subducted Tethyan slab. [ABSTRACT FROM AUTHOR]

The progressive indentation of India into Eurasia generated an E‐W‐trending orthogonal collision belt and a N‐S‐trending oblique collision belt. Compiling available data reveals that ∼70% of the Cenozoic igneous rocks in eastern and southeastern Tibet are concentrated within an ENE‐trending, ∼550–km long and ∼250–km wide magmatic zone (CMZ) that once separated the orthogonal and oblique collision belts. The Latitude 26°N Line is now its southern boundary. The onset timing of magmatism of the CMZ varies gradually from ∼55 Ma in the westernmost part to ∼27 Ma in the easternmost. Then the magmatism successively occurred and suddenly stopped at ∼25 Ma. The segmented and coherent chemical variation trends found suggest that the CMZ magmatic rocks were formed due to partial melting of the heterogeneous upper mantle and crusts of Eurasia. Subduction of Paleo‐ and Neotethyan oceanic plates generated this compositional and mineralogical heterogeneity. Combined with available geophysical data, the CMZ was diachronously formed in response to asthenosphere upwelling induced by NNW—SSE‐direction lithosphere stretching. The difference in responses of the orthogonal and oblique collision belts to the indentation of the Indian continent has led to this lithosphere stretching. [ABSTRACT FROM AUTHOR]

Lithospheric foundering is hypothesized to contribute to the formation of Earth's largest continental plateaus, but the predicted effects remain poorly constrained, especially considering variations in crustal strength. Here we propose that lithospheric foundering involving a hot, weak crust can explain aspects of topography and crustal deformation in mountain belts. We explore this hypothesis using numerical models of orogenesis and foundering in the Southern Puna Plateau in the Central Andes. Contrary to previous models of foundering involving a strong crust, which are characterized by subsidence and shortening, a weak crust results in surface uplift and upper‐crustal horizontal extension, which is accommodated by horizontal shortening in peripheral regions. Our model explains data such as the timing and location of exhumation and basin sedimentation as a response to foundering. The model also shows that foundering is capable of converting a high‐relief, broken‐foreland region into a high‐elevation, low‐relief plateau in a convergent tectonic setting. Plain Language Summary: Thickened crust can gravitationally unstable and founder into the mantle. This process could contribute to the formation of large plateaus such as Tibet and the Central Andes, which are composed of hot, felsic, and therefore weak crust. However, existing models have not thoroughly considered the implications of lithospheric foundering beneath a weak crust. We present numerical modeling experiments that show that a lithospheric drip can cause crustal flow and spreading, even when it takes place within a convergent tectonic setting, such as a major mountain belt. By comparing our models to geologic data from the Central Andes, we suggest that this scenario can explain many intriguing geological puzzles within the Puna Plateau, such as the timing and distribution of horizontal extension, the thickening of the crust, and the uplift history of the plateau. Future studies should consider the possibility of a weak, flowing crust during a lithospheric foundering event. Key Points: Lithospheric foundering under a hot, weak crust causes syn‐convergent, upper‐crustal extensionOur models successfully explain the Cenozoic uplift and deformation of the Puna Plateau as a result of this processThis style of foundering has been overlooked but may apply to other large orogens [ABSTRACT FROM AUTHOR]

The Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating ≥1,000 km‐long strike‐slip faults, and opening Tertiary rifts and oceanic basins up to ≈3,000 km away from the Himalayas. Modeling such broad‐scale tectonics has been challenging. While continent‐scale, lithospheric deformation appears to have been primarily taken‐up by long, narrow, inter‐connected shear‐zones with large offsets, the contribution of processes such as channel‐flow, collapse, delamination, etc... has remained contentious. Here, based on increasing 4G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modeling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, ≈55 Ma ago. The planar, 50 million km2, 125 km‐thick models are scaled for gravity. The approach permits mega‐fault generation and evolution without pre‐arranged initial settings. The results provide insight into fault birth, propagation and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike‐slip shear zones. Plain Language Summary: To better understand the Tertiary, three‐dimensional tectonics of South‐Eastern Asia, mostly a result of the north‐eastwards penetration of "rigid" India since ≈55 Ma, we use a Discrete Element Modeling approach. The technique permits the generation and evolution of large faults without initial pre‐setting. The model results substantiate the northwards growth of 4/5 Tibet sub‐plateaus, atop south‐dipping, subducted lithospheric slabs. Two long strike‐slip faults, comparable to the Ailao‐Shan‐Red River and Altyn Tagh‐Haiyuan shear zones, successively propagate to the eastern boundary of the model, where they generate extensional basins similar to the South China Sea and North China Rifts. They isolate two stable blocks (≈Sunda and South China). Remarkably, without changes in indentation rate, the activation of the northern shear zone triggers slip reversal on the southern one, as observed along Yunnan's Red River faults since the Miocene. On the west side of Sunda, the model generates faults comparable to the Sagaing fault and triangular basins similar to the Andaman and Mergui basins. Finally, the model suggests that crustal thickening across Tibet alternated with strike‐slip faulting. The main discrepancy between tectonic observations and model results is the striking difference in strike‐slip fault orientation, likely due to age‐dependent lithospheric strength. Key Points: Stepwise continental subduction and northward rise of Tibetan mountain ranges, and isolation of intervening captive basinsBirth and propagation of lithospheric continental shear zones, coupled with far‐field opening of rifts and Oceanic basinsContinental block extrusion and broad‐scale fault‐slip reversal [ABSTRACT FROM AUTHOR]

The origin and formation of the continental collision-related magmas remain elusive. The volcanic rocks erupted during India-Asia continental collision offer an ideal opportunity to explore their genesis and geodynamic process. Here, we report new zircon U-Pb dating results and Hf isotope, whole-rock element and Sr-Nd isotope data of volcanic rocks in Linzhou Basin, central Lhasa Terrane, southern Tibet. These volcanic rocks are mainly comprised of andesites and belong to Dianzhong Formation. The timing of their formation is ca. 63–66 Ma, coeval with the India-Asia continental initial collision in the central part of southern Tibet. All these rocks show an arc-like geochemical affinity and they have more depleted Sr-Nd-Hf isotopic compositions (87Sr/86Sri = 0.705006–0.705963, εNd(t) = −1.78 to 3.52, zircon εHf(t) = 1.2–7.0) than the Cretaceous pre-collisional andesites and Eocene ancient lithospheric mantle-derived melts beneath the central Lhasa Terrane. The correlation between Mg# and CaO, TiO2, Al2O3, Sr/Y, 87Sr/86Sr, εNd(t) suggests that they were likely hybrid production between an isotopically depleted end-member and the enriched lithospheric mantle (ELM). The oceanic crust-derived melts would be the best candidate for the former end-member according to their depleted Sr-Nd isotopic compositions. The andesitic rocks of Dianzhong Formation in the central Lhasa Terrane were most likely stemmed from partial melts of altered Neo-Tethyan crust and then mixed with the ELM-derived melts. Given the Cretaceous-Tertiary upper crustal shortening, back-arc extension, and voluminous volcanism in the Lhasa Terrane, along with abrupt increasing in the magma temperature and the convergence rate between India and Asia during Palaeocene, the occurrence of the Dianzhong Formation volcanic rocks can be well explained by the Neo-Tethyan slab roll-back. The mixing between the oceanic crust- and the continental lithospheric mantle-derived melts induced by the oceanic slab roll-back would be a complimentary scenario for the formation of the syn-collisional magmatism in collisional orogeny belts. [ABSTRACT FROM AUTHOR]

Rockfall in limestone mines is a common geohazard in the Changdu area of eastern Tibet and one of the leading geo-safety issues that mining enterprises and railway projects are faced with. We carried out a detailed geohazard survey using the methods of general geology, structural geology, and geohazard geology. We found the rockfall development pattern, characterized rock mass structural planes, discussed the collapse's mechanism, and established its failure mode. The results show that rockfall sites in the study area show a linear spreading along the fold and thrust zone. Five groups of steep-dip structural planes have developed in the rock body, including the longitudinal joint (S1), the transverse joint (S2), the X-type conjugate shear joints (S3 and S4), and the interlayer shear joint (S5). Paired with regional folds and hedging faults, these structural planes cut the rock mass into broken blocks. The collapses are the product of coupled internal and external dynamic geological processes. The sedimentary foundation of the rockfalls in the Qamdo area is the limestone from the upper Triassic Bolila Formation (T3b) formed in the intracontinental rift basin. The strongly folded orogeny triggered by the Cenozoic (Cz) India-Eurasia collision laid down the tectonic framework in the region, which is the essential condition for rockfall development. The strong Neotectonic movement since the Quaternary (Q), frequent hot and humid climate alternations with abundant rainfall since the Late Pleistocene (Q3), everyday human activities, and other internal and external dynamic coupling effects are the main triggering factors of the rockfall disaster. Three failure modes of rockfall are identified, namely toppling, falling, and sliding. The research results have specific guiding significance for rockfall prevention and control in the karst area and the railway construction in the Sichuan-Tibet area. [ABSTRACT FROM AUTHOR]

• UHP eclogites are overprinted by two phases of (U)HT metamorphism in Kunlun-Qaidam Massif. • The overprinting reveals thermal evolution from very high to intermediate and to low P/T type metamorphism. • It records tectonic transition from continental subduction to orogenic collapse. • The Kunlun-Qaidam Massif is a unique diffusive cryptic suture zone. Multiple high-temperature (HT) to ultrahigh-temperature (UHT) overprinting events on continental ultrahigh-pressure (UHP) terranes offer valuable insights into the tectonic evolution from subduction to orogenic collapse. However, the tectonic mechanisms driving the metamorphic evolution remain poorly understood. Herein, we present a detailed study integrating petrography, phase equilibria modeling, and zircon dating of a suite of eclogite, granulized eclogite, and mafic granulite samples from the Eastern Kunlun domain in the Kunlun-Qaidam Massif, North Tibet. Our work reveals three episodes of metamorphism: (1) peak-pressure UHP eclogite-facies metamorphism (>2.7–2.9 GPa, 700–740 °C) at ca. 450–430 Ma; (2) post-peak isothermal decompression under fluid/melt-absent conditions with the formation of symplectites, followed by decompression-heating with evolving P – T conditions from 1.3 to 1.2 GPa/750–780 °C to ∼0.9 GPa/840–870 °C at 423–410 Ma; and (3) continued decompressional heating culminating in UHT conditions of 0.7–0.4 GPa/∼980 °C at ca. 410–400 Ma. Combined with regional magmatic data, a four-stage tectonic model is proposed to explain our results: (a) the Proto-Tethys Ocean subduction during 537–450 Ma; (b) continental subduction and crustal thickening during 450–430 Ma; (c) tectonic underplating and crustal thinning during 430–410 Ma resulting from exhumation and lateral flow of the subducted material beneath a broad arc-backarc region after slab breakoff; and (d) post-collisional extension and orogenic collapse during 410–380 Ma triggered by lithosphere delamination and mantle upwelling. Our model implies that the transition from continental subduction to orogenic collapse occurred within 20 Myr, and also portrays that the formation of a unique diffusive cryptic suture zone characterized by tectonic mixtures of subducted materials and upper-plate sequences across the Kunlun-Qaidam Massif. [Display omitted] [ABSTRACT FROM AUTHOR]

Featured Application: Resource and environmental effects of the Tibetan Plateau. Himalayan orogenesis remains enigmatic in terms of Tibetan Plateau geodynamics originating from the Cenozoic India–Eurasian continental collision. India underthrusts below Tibet to the Yarlung–Tsangpo suture, which has been identified as the northernmost boundary for underplating. However, the way in which the historical evolution of continental subduction induces plateau uplift and the way it controls the variation in uplift between outboard and inboard areas is still unclear. To interpret the evolutionary mechanisms involved in the Himalayan growth history, we constructed different 3-D dynamic models at important stages to address these questions related to the formation of the Himalayas on the basis of paleoenthalpy evidence encoded in fossil leaves from recently documented assemblages in southern Tibet. The results show that (1) the effect of crustal thickening was the predominant factor in the early evolution from the Paleocene to the early Eocene, which resulted in a moderate growth rate. (2) The consecutive slab break-off eastward from the western syntaxis and the associated slab rebound significantly accelerated orogenesis from the late Eocene to the Oligocene. The upwelling asthenospheric flow was a key control of increasing crustal buoyancy, which resulted in the fastest growth of the Himalayas during the early Miocene. (3) Thereafter, the gradually enhanced monsoon and surface erosion during accompanying the increasing mountain height resulted in a slowdown of the orogenic rate, which counterbalanced the buoyant force produced by asthenospheric flow driving continuous Himalayan growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-Mg and low-Mg adakitic rocks (ca. 204–212 Ma) were identified in the East Kunlun Orogen, Northern Tibet. • Juvenile Crustal reworking with crust-mantle magma mixing controls the arc crustal evolution. • The late Triassic adakitic rocks were formed in a post-collision extensional setting. Adakitic rocks found within continental arcs are pivotal in unraveling the geodynamic processes and tectonic evolution of East Kunlun Paleo-Tethyan orogen. We present an integrated study on the petrography, zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopes of newly identified Late Triassic adakitic plutons in the East Kunlun Orogenic Belt (EKOB), Northern Tibet, aiming to constrain their petrogenesis and geodynamic implications. These plutons comprise by mylonitized granite, monzogranite, granodiorite and dioritic porphyrite, exhibiting consistent zircon U-Pb ages of approximately 204–212 Ma. They have high SiO 2 , K 2 O and Sr (average of 479 ppm) contents, but low contents of Y (5.6–18 ppm) and Yb (0.5–1.0 ppm) with high Sr/Y ratios (17–63), resembling adakitic rocks. These adakitic rocks can be classified into high-Mg (Mg#= ∼51) and low-Mg groups (Mg#= ∼35), although they all display enriched large ion lithophile elements and light rare earth elements but depleted high field strength elements. The studied low-Mg adakitic rocks have low MgO (∼0.68 wt%) and Cr (∼35 ppm) with enriched zircon Hf isotopes (εHf(t) = − 1.16 t 2.44), suggesting their derivation by partial melting of thickened juvenile crust. Conversely, the high-Mg adakitic rocks exhibit high MgO (∼1.94 wt%) and Cr (∼61 ppm) with relatively high zircon εHf(t) values (−0.68 to 4.95), indicating their derivation from foundered crustal root with subsequent interaction with enriched mantle-derived magma. Tectonic reconstructions suggest that the formation of these Late Triassic adakitic rocks occurred in a post-collisional extension setting and the East Kunlun Paleo-Tethyan Ocean closed no later than Norian. [ABSTRACT FROM AUTHOR]

The tectonic-thermal mechanism of crustal melting provides vital information on continental differentiation and orogenic evolution. This study aims to understand the evolution and tectonic setting of newly discovered lower crustal leucosome-rich granulites of the Qilian Orogen, NW China. Tonalitic leucosome within garnet amphibolite occurs in net-like arrays or as stringers and has diffuse boundaries with the host, with enriched LILE, and high Sr and Sr/Y ratios, similar to that of adakite, formed by water-fluxed melting. However, granitic leucosome within garnet granitic gneiss shows sharp contacts with the host, and has low Sr, Ba, K and Pb but high Rb, Rb/Sr, with negative Eu anomalies, consistent with dehydration melting. Petrographic observations, geochemical data and pseudosection modelling suggest that garnet amphibolite experienced water-fluxed melting and garnet granitic gneiss underwent dehydration melting, respectively. LA-ICP-MS zircon and titanite dating indicate the anatectic event proceeded at ∼480–470 Ma. Phase equilibrium modelling suggests the garnet amphibolite and garnet granitic gneiss share a similar P-T path involving decompression heating from ∼12.1 kbar/711–746 °C to reach peak temperatures of 798–836 °C at 10.4 kbar, and subsequently decompression cooling to 4.6–7.6 kbar/600–672 °C. The calculated P-T conditions suggest Barrovian-type metamorphism with thermal gradients of 24.2 °C/km for the Central Qilian lower crust. We interpret a retro−/back-arc setting resulting from the southward subduction of the North Qilian oceanic lithosphere. [Display omitted] • Water-fluxed melting of hornblende and dehydration melting of biotite in the crust root. • An anatectic event proceeded at ca. 480–470 Ma in the Central Qilian belt. • A hot retro−/back-arc setting is proposed to provide enough heat for anatexis and metamorphism. [ABSTRACT FROM AUTHOR]

The timing and mechanism of uplift in the southeastern Tibet Plateau have long been subjects of debate. The Gongga Shan region, positioned at the convergence of the Songpan-Ganzi, Chuandian, and Yangtze blocks, serves as a crucial vantage point for unraveling the evolutionary history of the southeastern Tibet Plateau. Nevertheless, the uplift history of the Gongga Shan region remains shrouded in uncertainty. By employing multivariate trace element ratios and reconstructing crustal thickness using zircon Eu/Eu*, our research has unveiled distinct periods of crustal thickening and thinning events. Within the time span of ∼240–160 Ma, a discernible thickening trend emerged from ∼35 to ∼45 km between ∼240 and ∼ 215 Ma, followed by a relatively stable phase from ∼215 to ∼170 Ma, and subsequently a decline from ∼170 to ∼160 Ma, reducing the thickness from ∼45 to ∼30 km. In the period from ∼55 to ∼5 Ma, an initial increase in thickness occurred from ∼30 to ∼60 km between ∼55 and ∼ 30 Ma, succeeded by an overall thinning from ∼60 to ∼35 km between ∼30 and ∼ 10 Ma. Moreover, based on our reconstructed crustal thickness data, we have traced the paleo-elevation changes in the Gongga Shan region from the Cenozoic to the present, revealing a fluctuation from ∼0.5 to ∼4.5 km. We attribute the Triassic-Jurassic crustal thickening and subsequent thinning to the Triassic orogeny and post-collision extension following the closure of the Paleo-Tethys Ocean. Our findings further suggest that during the Eocene-Oligocene period, the Gongga Shan region experienced significant crustal thickening and surface uplift, indicative of intense compression. This phenomenon likely resulted from the northeast-directed compression of the Indian-Eurasian plate, causing substantial crustal shortening and thickening in specific areas of the southeastern Tibet Plateau, leading to rapid surface uplift. Subsequently, during the Oligocene-Miocene, the detachment and subsidence of the lithospheric mantle triggered rapid crustal thinning in the Gongga Shan region. This phase was accompanied by relatively stable and slight surface uplift, signifying a shift in the plateau uplift mode of the southeastern Tibet Plateau from compression to lateral extrusion. • 959 new detrital zircon trace elements data from the Gongga Shan are reported. • Zircon Eu/Eu* shows significant crustal thickening occurred between ∼55 and ∼ 30 Ma. • Paleo-elevation reconstruction reveals ∼4 km of plateau growth in the Cenozoic. [ABSTRACT FROM AUTHOR]

The Longmenshan Thrust Belt in Eastern Tibet resulted from a Mesozoic orogeny and Cenozoic reworking. It is generally believed that the Cenozoic tectonics along the Longmenshan Thrust Belt are mostly inherited from the Mesozoic. Reconstructing the Mesozoic tectonics of the Longmenshan Thrust Belt is therefore important for understanding its evolutionary history. On the basis of detailed structural analysis, we recognized a Main Central Boundary that divides the Longmenshan Thrust Belt into a Southeastern Zone and a Northwestern Zone. Both zones underwent a main D1 event characterized by D1E top-to-the-SE thrusting in the Southeastern Zone and D1W top-to-the-NW/N thrusting in the Northwestern Zone. In the Southeastern Zone, a D2 top-to-the-NW/N normal faulting that cuts the D1E structures is developed along the NW boundary of the basement complexes. Newly obtained and previous geochronological data indicate that the D1E and D1W events occurred synchronously at ca. 224-219 Ma, and the D2 top-to-the-NW/N normal faulting was episodically activated at ca. 166-160 Ma, 141-120 Ma, 81-47 Ma, and 27-25 Ma. Episodic and synchronously activated top-to-the-NW normal faulting and top-to-the-SE thrusting along the northwestern and southeastern boundaries of the basement complexes, respectively, leads us to propose that the basement slices were episodically imbricated to the SE during the Late Jurassic--Early Cretaceous and Late Cretaceous--earliest Paleocene. The D1 amphibolite facies metamorphic rocks above the basement complexes recorded fast exhumation during the Late Jurassic--Early Cretaceous. We propose that the early Mesozoic northwestward basement underthrusting along a crustal "weak zone" was responsible for the D1 double-vergent thrusting and amphibolite facies metamorphism. Subsequent basement-slice imbrications reworked the Longmenshan Thrust Belt and exhumed the amphibolite facies rocks. Our results highlight the importance of basement underthrusting and imbrication in the formation and reworking of the intracontinental Longmenshan Thrust Belt in Eastern Tibet. [ABSTRACT FROM AUTHOR]

The Tethys Himalaya tectonic belt has long been a passive continental margin north of Gondwana, commonly known as the Tethys Himalaya, which Indo-Asian collision orogeny developed until the Cenozoic era. It is of great scientific significance to determine its geo-tectonic evolution over geological history. Therefore, to reveal the geodynamic background of the Late Cretaceous Tethys Himalaya and its internal connection with the subduction of the Neo-Tethys ocean, in this study, we analysed the petrology, and whole-rock geochemistryof the Zongzhuo Formation basalt, which is widely distributed in the Tethys Himalaya Rongbu area. Further, we investigated the basalt types, magma source, tectonic setting and causes that gave rise to the Zongzhuo Formation to further research on the evolution of the Tethys Himalaya tectonic domain. The Zongzhuo Formation features a basalt set of compatible elements and is characterised by low Cr (average: 86.838 ppm) and enrichment of high-field-strength elements (e.g. Nb, Ta and Hf). The characteristics of the major elements, i.e. high TFeO (average: 10.43 wt %), TiO2 (average: 3.44 wt %) and P2O5 (average: 0.47 wt %), indicate an oceanic–island–basalt (OIB) geochemical signature with obvious light REE and heavy REE fractionation. The characteristics of the trace elements confirm the alkalinity of the Zongzhuo Formation basalts. Based on these results, the Zongzhuo Formation basalt was assigned to within–plate OIB. The magma might be the metasomatism products of the oceanic lithosphere mantle with low crystal fractionation and no crustal contamination, its tectonic background includes a passive–to–active transformation in the continental margin. By analysing the Tethys Himalaya belt in the south of Tibet, we concluded that the Zongzhuo Formation basalt strata in the Rongbu area were likely formed owing to Mesozoic volcanic activity and the extension and thinning of the Tethys Himalaya in the area. [ABSTRACT FROM AUTHOR]

More than 200 years since its initial exploration, Zanda Basin, a high-elevation (3,800–4,500 m above sea), intermountain basin at the foothills of the Himalaya, is the site to some of the earliest fossil discoveries, including the holotype of extinct Tibetan antelope, Qurliqnoria hundesiensis. These fossils also hold the record, in 1823, as the first vertebrate fossils from Tibet in the scientific literature. Unfortunately, these tantalising early records have become all but forgotten for more than 100 years due to a lack of information about their localities. Our recent explorations in the 2000s revive the interests in Zanda Basin and establish a unique Zanda mammal assemblage important in the evolution of Tibetan Neogene mammals. In this paper, we retrace the expedition routes by early explorers and attempt to establish, to the extent possible, the type locality of two key mammals in the Zanda fauna: Q. hundesiensis and Hipparion (Plesiohipparion) zandaense. We highlight the pivotal role Zanda fossil mammals play in the early discourse of mountain building, climate change, and mammal adaptation in high Himalaya, more than a hundred years before Chinese palaeontologists made a similar argument upon the discovery of three-toed horses, in the 1980s, at different basins in Tibet. [ABSTRACT FROM AUTHOR]

There has been considerable debate concerning the petrogenesis of Cenozoic highly felsic, strongly peraluminous, leucogranites within the Himalayan–Tibetan orogen, with two contrasting viewpoints regarding their origin, either as primary melts from parting melting or magmatic differentiation. This debate hampers our understanding of the tectono‐magmatic evolution and associated uplift and exhumation processes during Himalayan orogenesis. This study attempts to resolve this debate by means of an integrated petrographic, geochronological, and geochemical study on the Cenozoic Cuonadong leucogranites (including two‐mica granites, garnet‐bearing granites, and tourmaline‐bearing granites) in the eastern part of the south Himalayan–Tibetan orogen. One SHIRIMP zircon U–Pb dating of two‐mica granites and four LA–ICP–MS monazite U–Th–Pb dating of all three types of granites yield ages of ca. 21.9–19.7 Ma. Combined with previous published continuous U–Th–Pb zircon/monazite ages varying from 16.5 to 21.8 Ma, indicating that Cuonadong leucogranites have experienced continuously multiple episodes of intrusion and long‐term crystallization from ca.16 to 22 Ma, and lasted for ca. 6 Myrs. Major and trace element geochemistry combined with whole‐rock Sr–Nd isotope data suggest that the Cuonadong's three types of leucogranites are highly fractionated and garnet‐ and tourmaline‐bearing granites are more evolved. The Cuonadong leucogranite melts are mainly derived from metapelites within the High Himalayan Crystalline Sequence, and underwent fractional crystallization of biotite, monazite, and plagioclase during melt migration. This study indicates Cuonadong leucogranites are Cenozoic highly fractionated strongly peraluminous leucogranites, which, combined with previous intermittent documentations of fractionated leucogranites, point to an increasing maturation of the continental crust composition during continental orogenesis. [ABSTRACT FROM AUTHOR]

Recent studies have indicated that an Andean- type orogen (Lhasaplano) developed on the Lhasa block in the Cretaceous during northward subduction of Neo-Tethyan oceanic lithosphere. When and how uplift of the Lhasaplano began, however, has remained controversial. This article integrates stratigraphic, sedimentological, tectonic, and provenance data from the latest marine to nonmarine strata in the Linzhou Basin to pinpoint the early topographic growth in southern Tibet. The Takena Formation mainly consists of lagoonal carbonates and mudstones yielding foraminiferal assemblages of Early Aptian age (ca. 123-119.5 Ma). The conformably overlying lower member of the Shexing Formation, mainly deposited in fluvial environments, was fed by volcanic and sedimentary rock fragments from the north Lhasa terrane. Clasts of the Gangdese arc to the south firstly appeared in the middle member and became dominant in the upper member of the Shexing Formation. By contrast, coarse grained, braided river facies occur in the uppermost part of the Shexing Formation, where detritus was mostly recycled from Paleozoic strata of north Lhasa, with minor volcaniclastic contribution from the Gangdese arc. Basin analysis indicates accelerating subsidence and sedimentation rates during deposition of Takena to middle Shexing strata (ca. 125-108 Ma), followed by steady subsidence during deposition of upper Shexing strata (ca. 108-96 Ma). Given this regional tectonic and sedimentary evidence, such an evolution is interpreted to reflect tectonic extension followed by thermal subsidence. Basin inversion and regional compression initiated during deposition of the uppermost Shexing strata (ca. 96 Ma), as indicated by active thrust faults and widespread accumulation of syntectonic conglomerates in the western part of the Lhasa block. This event marked the beginning of the Andean-type orogeny in southern Tibet. Such a paleotectonic evolution, from extension to tectonic inversion, is also documented in the Andes mountain range. It may be typical of the early stage growth of Andean-type active continental margins. [ABSTRACT FROM AUTHOR]

The mechanism of crustal deformation and the development of large offset strike‐slip faults during continental collision, such as the India‐Eurasia zone, remains poorly understood. Previous mechanical models were simplified which are either (quasi‐)2‐D approximations or made the a priori assumption that the rheology of the lithosphere was either purely viscous (distributed deformation) or purely localized. Here we present three‐dimensional visco‐elasto‐plastic thermo‐mechanical simulations, which can produce both distributed and highly localized deformation, to investigate crustal deformation during continental indentation. Our results show that large‐scale shear zones develop as a result of frictional plasticity, which have many similarities with observed shear zones. Yet localized deformation requires both a strong upper crust (>1022 Pa·s) and a moderately weak middle/lower crust (~1020 Pa·s) in Tibet. The brittle shear zones in our models develop low viscosity zones directly beneath them, consistent with geological observations of exhumed faults, and geophysical observations across active faults. Plain Language Summary: Large offset strike‐slip faults are one of the key surface features of continental collision, such as in Tibet. These narrow belts of strike‐slip faults accommodate strong deformation, and deciphering their mechanism of formation helps to understand the complex dynamics of India‐Eurasia collision. Yet previous models developed to address this either assumed simplified rheologies or employed low numerical resolutions that is insufficient to simulate the spontaneous formation of localized zones. Here, we present high‐resolution 3‐D visco‐elasto‐plastic thermo‐mechanical models that simulate the formation of large‐scale strike‐slip faults during Indian indentation, while also taking distributed deformation into account. Our simulations show that a combination of a strong upper crust and a moderately weak middle/lower crust produces faults that are, to first order, consistent with observed ones in the Tibet region. Localized deformation usually initiates at the brittle‐ductile transition, and a weak middle/lower crust facilitates subsequent shear localization such that the shear zones cut through the whole crust. The craton‐like strong terranes can sustain large stresses and initiate large offset faults along their boundaries. Key Points: 3D VEP high‐resolution thermomechanical models accounting for both localized and distributed deformation during India‐Eurasia collisionMajor strike‐slip faults develop preferentially in models with a strong upper and a moderately weak lower crustLower crustal flow and strong terranes surrounding Tibet facilitate fault formation [ABSTRACT FROM AUTHOR]

The lithospheric mantle beneath Archean cratons is conspicuously refractory and thick compared to younger continental lithosphere (Jordan, 1988; Boyd, 1989 ; Lee and Chin, 2014), but how such thick lithospheres formed is unclear. Using a large global geochemical database of Archean igneous crustal rocks overlying these thick cratonic roots, we show from Gd/Yb– and MnO/FeO T –SiO 2 trends that crustal differentiation required continuous garnet fractionation. Today, these signatures are only found where crust is anomalously thick (60–70 km), as in the Northern and Central Andes and Southern Tibet. The widespread garnet signature in Archean igneous suites suggests that thickening occurred not only in the lithospheric mantle but also in the crust during continent formation in the late Archean. Building thick crust requires tectonic thickening or magmatic inflation rates that can compete against gravitational collapse through lower crustal flow, which would have been enhanced in the Archean when geotherms were hotter and crustal rocks weaker. We propose that Archean crust and mantle lithosphere formed by thickening over mantle downwelling sites with minimum strain rates on the order of 10−13–10−12 s−1, requiring mantle flow rates associated with late Archean crust formation to be 10–100 times faster than today. [ABSTRACT FROM AUTHOR]

Amphibolite- and granulite-facies metamorphic rocks are common in the eastern Himalayan syntaxis of southeastern Tibet. These rocks are composed mainly of gneiss, amphibolite and schist that underwent various degrees of migmatization to produce leucogranites, pegmatites and felsic veins. Zircon U–Pb dating of biotite gneiss, leucocratic vein and vein granite from the syntaxis yields consistent ages of ∼49 Ma, indicating crustal anatexis during continental collision between India and Asia. Garnets in these rocks are categorized into peritecitc and anatectic varieties based on their mode of occurrence, mineral inclusions and major- and trace-element zoning. The peritectic garnets mainly occur in the biotite gneiss (mesosome layer) and leucocratic veins. They are anhedral and contain abundant mineral inclusions such as high-Ti biotites and quartz, and show almost homogeneous major-element compositions (except Ca) and decreasing HREE contents from core to rim, indicating growth during the P - and T -increasing anatexis. Peak anatectic conditions at 760–800°C and 9–10·5 kbar are well constrained by phase equilibrium calculations, mineral assemblages, and garnet isopleths. In contrast, anatectic garnets only occur in the vein granite. They are round or subhedral, contain quartz inclusions, and exhibit increasing spessartine and trace-element contents from core to rim. The garnet–biotite geothermometry and the garnet–biotite–plagioclase–quartz geobarometry suggest that the anatectic garnets crystallized at ∼620–650°C and 4–5 kbar. Some garnet grains show two-stage zoning in major and trace elements, with the core similar to the peritectic garnet but the rim similar to the anatectic garnet. Mineralogy, whole-rock major- and trace-element compositions and zircon O isotopes indicate that the two types of leucosomes were produced by hydration (water-present) melting and dehydration (water-absent) melting, respectively. The leucocratic veins contain peritectic garnet but no K-feldspar, have lower whole-rock K2O contents and Rb/Sr ratios, higher whole-rock CaO contents and Sr/Ba ratios, and show homogeneous δ18O values that are lower than those of relict zircons, indicating that such veins were produced by the hydration melting. In contrast, the vein granite contains peritectic garnet and K-feldspar, has higher whole-rock K2O contents and Rb/Sr ratios, lower whole-rock CaO contents and Sr/Ba ratios, and shows comparable δ18O values with those of relict zircons, suggesting that this granite were generated by the dehydration melting. Accordingly, both hydration and dehydration melting mechanisms have occurred in the eastern Himalayan syntaxis. [ABSTRACT FROM AUTHOR]

The Lhasa terrane of the southern Tibetan Plateau participated in a Mesozoic Andean-type orogeny caused by the northward subduction of the Neo-Tethyan oceanic lithosphere. However, metamorphic rocks, which can unravel details of the geodynamic evolution, are rare and only exposed in the south-eastern part of the Lhasa terrane. Therefore, we conducted a detailed petrological, geochemical and U–Pb zircon geochronological study of the late Cretaceous metamorphic rocks and associated gabbros from the Nyemo inlier of the southern Lhasa terrane. The Nyemo metamorphic rocks including gneisses, schists, marbles and calc-silicate rocks, experienced peak amphibolite-facies contact metamorphism under P–T conditions of 3.5–4.0 kbar and 642–657 °C with a very high geothermal gradient of 45–50 °C/km, revealing a distinct deflection from the steady-state geotherm during low-pressure metamorphism. Inherited magmatic zircon cores from the metamorphic rocks yielded protolith ages of 197–194 Ma, while overgrowth zircon rims yielded metamorphic ages of ca. 86 Ma. Whole-rock chemistry and zircon Hf isotopes suggest that the protoliths of the gneisses and schists are andesites and tuffs of the early Jurassic Sangri Group, which were derived from a depleted mantle source of a continental arc affinity. The coeval intimately-associated gabbro (ca. 86 Ma) crystallized under P–T conditions of 3.5–5.3 kbar and 914–970 °C, supplying the heat flux high enough to cause the contact metamorphism of the Sangri Group rock types. We propose that the intrusion of the gabbro and a simultaneous pressure increase of up to 4.0 kbar, which is related to crustal thickening due to crustal overthrusting and the intrusion of mafic material, resulted in the late Cretaceous metamorphism of the early Jurassic Sangri Group during an Andean-type orogeny. Furthermore the Nyemo metamorphic rocks, which have previously been considered to represent slivers of the Precambrian metamorphic basement of the Lhasa terrane, are late Cretaceous metamorphic supracrustal rocks. [ABSTRACT FROM AUTHOR]

Abstract: The Zhaxikang Pb‐Zn‐Ag‐Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein‐type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping vein‐type orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N–S‐striking normal fault system. This deposit records multiple stages of mineralization that include an early period (A) of massive coarse‐grained galena–sphalerite deposition and a later period (B) of Sb‐bearing vein‐type mineralization. Period A is only associated with galena–sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite–sphalerite–pyrite, quartz–sulfosalt–sphalerite, calcite–pyrite, quartz–stibnite, and quartz‐only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre‐existing Pb–Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive open‐space filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low–medium temperature (187–267°C) and low salinity (4.00–10.18% wt. NaCl equivalent) ore‐forming fluids, although variations in the physical–chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with FeS concentrations of 8.999–9.577, 7.125–9.109, 5.438–1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable (4‰–13‰), varying from 4‰ to 11‰ in period A and 10‰ to 13‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206Pb/204Pb vs. 207Pb/204Pb and 206Pb/204Pb vs. 208Pb/204Pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb–Zn sulfides and regional Sb‐bearing fluids. These features are indicative of overprinting and remobilization of pre‐existing Pb–Zn sulfides by Sb‐bearing ore‐forming fluids during a post‐collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang‐style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb–Zn exploration in these areas. [ABSTRACT FROM AUTHOR]

Evolutionary biology has long been concerned with how changing environments affect and drive the spatiotemporal development of organisms. Coelotine spiders (Agelenidae: Coelotinae) are common species in the temperate and subtropical areas of the Northern Hemisphere. Their long evolutionary history and the extremely imbalanced distribution of species richness suggest that Eurasian environments, especially since the Cenozoic, are the drivers of their diversification.We use phylogenetics, molecular dating, ancestral area reconstructions, diversity, and ecological niche analyses to investigate the spatiotemporal evolution of 286 coelotine species from throughout the region. Based on eight genes (6.5 kb) and 2323 de novo DNA sequences, analyses suggest an Eocene South China origin for them. Most extant, widespread species belong to the southern (SCG) or northern (NCG) clades. The origin of coelotine spiders appears to associate with either the Paleocene-Eocene Thermal Maximum or the hot period in early Eocene. Tibetan uplifting events influenced the current diversity patterns of coelotines. The origin of SCG lies outside of the Tibetan Plateau. Uplifting in the southeastern area of the plateau blocked dispersal since the Late Eocene. Continuous orogenesis appears to have created localized vicariant events, which drove rapid radiation in SCG.North-central Tibet is the likely location of origin for NCG and many lineages likely experienced extinction owing to uplifting since early Oligocene. Their evolutionary histories correspond with recent geological evidence that high-elevation orographical features existed in the Tibetan region as early as 40-35 Ma. Our discoveries may be the first empirical evidence that links the evolution of organisms to the Eocene-Oligocene uplifting of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The role of northern Tibet in the Cenozoic climate evolution in East Asia remains controversial owing to a lack of constraints on the timing and pattern of mountain building. The East Kunlun Shan (EKLS) defines the geomorphological boundary of the northeastern Tibetan Plateau. We employed apatite (U Th)/He thermochronology to analyze the exhumation history and pattern across the EKLS. In this study, we presented 28 mean apatite (U Th)/He ages of bedrock, including seven previously published ages. Observed ages decrease with the decreased distance from the Kunlun strike-slip fault (34.0 to 20.4 Ma). Age-elevation relationships and thermal modeling demonstrate that exhumation rates in the EKLS and in restraining bends along the Kunlun strike-slip fault increased by a factor of 5–10, reaching ∼200 m/Myr at ∼26 Ma. These exhumation patterns support the idea that mountain building of the EKLS initiated in the Late Oligocene through northward tilting around the same time with strike-slip motion along the Kunlun fault. When combined with existing geological data, our findings suggest that the northern margin of high Tibet expanded from Tanggula Shan to EKLS-West Qinling during the Late Oligocene to Early Miocene. This period coincides with the initial accumulation of loess at the front of northern Tibet and the northward expansion of the monsoon region in adjacent East China. Therefore, our work supports the notion that the northward growth of Tibet may have played a role in the Late Oligocene-Early Miocene climate reorganization in East Asia. • Accelerated exhumation at ∼26 Ma in the East Kunlun Shan • Late Oligocene initial uplift related to the tilting of the entire East Kunlun Shan • Coincidence between northward growth of Tibet and climate changes in East Asia [ABSTRACT FROM AUTHOR]

The present northwest-trending Altai mountains, as far as ∼2000 km north of the Indian–Asian collision front, are dominated by a transpressional strike-slip fault system, and are generally considered as one of distant tectonic effects of the ongoing India–Asia collision. However, the Cenozoic reactivation of the Altai and its linkage with the tectonic evolution of the Tibet plateau remain mechanically challenging. Here, we constructed large-scale 2D numerical models with inherited lithospheric heterogeneities from India to Altai representing the onset of the India–Asia collision. The sensitivity of model results to variable thermo-mechanical and geometric properties of the orogen-like Tibet and Altai as well as variable thermal state of the craton-like India and Junggar reveals that both the particular lithospheric architecture of western Tibet and basement structural inheritance of central Asia regulate the long-distance deformation propagation from the India–Asia plate boundary to the Altai–Sayan region. The model results indicate that the direct collision of the underthrusting Indian lithosphere with the rigid Tarim block beneath western Tibet plays a dominant role in the ultra-long-distance deformation propagation to central Asia. As less-deformed rigid blocks, the Tarim and Junggar basins with Precambrian basements serve as secondary indenters that transfer the compressive stresses extensively to the Altai–Sayan region. Constrained by substantial surface geology and geophysical observations, this numerical study recognizes the linkage between the evolving lithospheric structure of western Tibet with the northward younging trend of reactivation of the orogenic belts in central Asia. By means of the rigid Indian–Tarim lithospheric mantle collision, the plate-convergence stress can be effectively transmitted through Tarim to Tian Shan and subsequently through Junggar to Altai, leading to successive reactivation of the Tian Shan and Altai mountains. The locations of reactivation are determined by the inherited structural zones of lithospheric weakness that formed during the Paleozoic assembly of the Central Asian Orogenic Belt. [Display omitted] • India–Tarim lithospheric mantle collision triggered deformation propagation to Altai. • The Tarim and Junggar blocks serve as a secondary indenter for stress transfer. • The reactivation of Tian Shan and Altai is followed by uplift of the Tibetan plateau. • The convex structure of Tarim and Junggar is due to strong north-south compression. [ABSTRACT FROM AUTHOR]

Mass elevation and lee effects markedly influence snow lines and tree lines in high mountain systems. However, their impact on other phenomena or groups of organisms has not yet been quantified. Here we quantitatively studied their influence in the Himalaya–Tibet orogen on the distribution of ground beetles as model organisms, specifically whether the ground beetle distribution increases from the outer to the inner parts of the orogen, against latitudinal effects. We also tested whether July temperature and solar radiation are predictors of the beetle’s elevational distribution ranges. Finally, we discussed the general importance of these effects for the distributional and evolutionary history of the biota of High Asia. We modelled spatially explicit estimates of variables characterizing temperature and solar radiation and correlated the variables with the respective lower elevational range of 118 species of ground beetles from 76 high-alpine locations. Both July temperature and solar radiation significantly positively correlated with the elevational ranges of high-alpine beetles. Against the latitudinal trend, the median elevation of the respective species distributions increased by 800 m from the Himalayan south face north to the Transhimalaya. Our results indicate that an increase in seasonal temperature due to mass elevation and lee effects substantially impact the regional distribution patterns of alpine ground beetles of the Himalaya–Tibet orogen and are likely to affect also other soil biota there and in mountain ranges worldwide. Since these effects must have changed during orogenesis, their potential impact must be considered when biogeographic scenarios based on geological models are derived. As this has not been the practice, we believe that large biases likely exist in many paleoecological and evolutionary studies dealing with the biota from the Himalaya-Tibet orogen and mountain ranges worldwide. [ABSTRACT FROM AUTHOR]

Forming the northwestern branch of the Chinese Tian Shan, the Keguqin mountain located north of the Yili basin is characterized by Mesozoic relict landscapes and active faults, which recorded abundant information of long term tectono-geomorphologic evolution of the Tian Shan mountain range. However, the post-Jurassic deformation history of the Keguqin mountain is unclear. In this study, we applied apatite fission track, apatite (U Th)/He and geomorphologic analyses to reconstruct the landscape evolution of the Keguqin mountain and the northern Yili basin. Our results suggest that this region underwent three stages of accelerated cooling/exhumation in the Permian, Late Triassic-Jurassic and Cretaceous. The Permian cooling event likely reflects post magmatic cooling related to the Paleozoic orogeny of the Tian Shan. Late Triassic-Jurassic exhumation is possibly a far field response of the Qiangtang collision. The Cretaceous differential exhumation in the study area was controlled by activation of the Kashihe fault zone and secondary faults. As the Cretaceous cooling is widely observed in the vast Central Asia region, northern Tibet and Southern Pamir, and coeval with the Mongol-Okhotsk orogeny, Qiangtang collision and Karakorum collision. It is difficult to decipher the tectonic drive of the Cretaceous activation of the Kashihe fault zone. Relict landscapes in the Keguqin mountain were firstly established after the Paleozoic, slightly exhumed during the Cretaceous, and were uplifted and tilted by Late Cenozoic deformation. The latest uplift magnitude of the Keguqin mountain is estimated to be ∼250–500 m and ∼ 380–430 m of the hanging wall of the Kashihe fault zone and the Keguqin fault, respectively. • The Keguqin mountain has experienced three stages of cooling/exhumation in in the Permian, Late Triassic-Jurassic and Cretaceous. • The Late Triassic-Jurassic exhumation of the Keguqin mountain was probably far field reponse of the Qiangtang collision. • The Cretaceous differential exhumation represents the reactivations of the Kashihe fault zone. • The latest uplift magnitude is estimated to be ∼250–500 m and ∼ 380–430 m on the hanging wall of the Kashihe fault zone and the Keguqin fault, respectively, in the Keguqin mountain. [ABSTRACT FROM AUTHOR]

The Tibetan region underwent diachronous differential rises during the Cenozoic era. Its elevation history is critical for understanding the processes of mountain building, and for evaluating its climatic effects on atmospheric circulations. However, knowledge of paleoenvironment and paleoelevation in different geological domains of the Tibetan Plateau is still limited. Here we provide chronology of lacustrine deposits of the Upper Dingqing Formation in the Lunpola Basin in Central Tibet, which yields a middle Miocene age (15–12 Ma). Both stable isotope and palynological records indicate a climatic transition at ∼13.8 Ma marked by a change towards a cooler and drier climate after the Middle Miocene Climate Transition driven by global climatic cooling. Pollen and spore assemblages suggest that the vegetation was dominated by mixed coniferous–broadleaved forest with some grasslands. New palynological elevation reconstructions constrained by the co-existence approach yield a maximum paleo-elevation of 3100–3600 m (average 3350 m) of the Lunpola Basin, which was consistent with a maximum elevation of 3400 m based on floating-leaf plants. Our new data do not support previous views that the Lunpola Basin achieved its current elevation as early as the late Eocene or early Oligocene, but instead we suggest there has been a rise of up to 1200 m since 12 million years ago. Our results bring new light on both the paleoenvironmental reconstructions and the paleo-elevation estimates of the Lunpola Basin, Central Tibet. • Mid-Miocene age (15–12 Ma) of the upper Dingqing Formation in Central Tibet. • Climatic shifted to a cooler/drier climate after ca.13.8 Ma in Central Tibet. • The vegetation was dominated by mixed coniferous–broadleaved forest at 15–12 Ma. • The Lunpola Basin only attained a maximum elevation of 3400 m in the middle Miocene. [ABSTRACT FROM AUTHOR]

This paper reviews the spatial-temporal distribution, geological and geochemical features, and geophysical context of diverse types of Cenozoic ore deposits formed during India-Eurasia continental collision in Tibet, in order to shed new light on their genesis and their control by mantle lithosphere. The parental magmas for porphyry-skarn Cu (± Mo ± Au) deposits were derived from metal-rich pre-Cenozoic juvenile crust, and the high magma oxidation state was controlled by involved mantle-derived basic magmas and thickened crust condition; magma emplacement was controlled by structures related both to tears in the subducting continental slab to deep and to mantle-crust decoupling parts at depth. Orogenic Au deposits mostly formed intermittently from hydrothermal fluids formed by devolatilization of earlier-fertilized mantle lithosphere that was triggered by asthenosphere upwelling; they were largely controlled by lithosphere-scale shear systems that reactivated earlier-formed suture zones. Giant MVT Zn Pb deposits, hosted by ancient oil reservoirs, formed during salt diapirism and infiltration of metal-rich basinal brines related to crustal-scale channel flow. The diverse range of ore deposits was derived predominantly through release of metal and fluid components, introduced into the crust and mantle lithosphere that occurred in the earlier oceanic subduction during anomalous lithosphere-scale deformation. The metallogenic history of collisional orogens contrasts with those of accretionary orogens. • Tibetan mineralization system provides an important global insight into metallogenesis during continental collision. • Lithosphere architecture and fertility formed by oceanic subduction control diverse ore deposits in collision setting. • Diverse types of Tibetan ore deposits have different genesis to those from oceanic subduction settings. • Tibetan ore deposits formed in various geodynamic settings of thrusting, shearing, rotation, and rifting. [ABSTRACT FROM AUTHOR]

Post-collisional granites are widely distributed in continental collision orogenic belts, and deciphering their petrogenesis has great bearings for understanding the deep crustal compositional and tectono-thermal evolution of collisional orogens. Here we carried out a combined study of whole-rock major-trace elements and Sr–Nd–Hf isotopes, and zircon U Pb ages and Lu Hf isotopes for late Paleozoic granites from the North Qaidam orogen, northeastern Tibet. The results indicate that they were derived from partial melting of subducted continental crust at high thermal gradients due to post-collisional rifting orogeny. Zircon U Pb dating of the granites yields weighted mean 206Pb/238U ages between 377 ± 3 Ma and 384 ± 5 Ma, which postdate the ultrahigh-pressure (UHP) metamorphic ages (ca. 438–420 Ma) of deeply subducted continental crust in the North Qaidam orogen. Therefore, they are products of post-collisional magmatism. Most relict zircons in the granites have concordant Neoproterozoic (793–972 Ma) and early Paleozoic (405–442 Ma) U Pb ages, generally consistent with the protolith and metamorphic ages of the UHP metaigneous rocks in the orogen, respectively. The granites are commonly calc-alkaline to high-K calc-alkaline with total alkali contents of 6.89–8.56 wt%, and weakly to moderately peraluminous with A/CNK values of 1.00–1.18 [A/CNK = Al 2 O 3 /(CaO + Na 2 O + K 2 O), in molar]. They exhibit arc-like trace element distribution patterns and enriched Sr–Nd–Hf isotope compositions with whole-rock (87Sr/86Sr) i ratios of 0.7074–0.7104, ɛ Nd (t) values of −9.0 to −4.4 and ɛ Hf (t) values of −4.2 to +2.9, and syn -magmatic zircon ɛ Hf (t) values of −7.6 to +7.7 (except one analysis of −15.0). These granites mostly have comparable Sr Nd isotope compositions to the UHP orthogneiss and continental eclogite in this collisional orogen, indicating their derivation from the subducted continental crust. Using the average compositions of the orthogneiss and continental eclogite in the orogen as the starting materials, phase equilibrium modelling results suggest that the whole-rock major elements of the post-collisional granites can be explained by the mixed melts mainly derived from these two lithologies, which were partially melted at high thermobaric ratios of 1156–1867 °C/GPa associated with different water contents (1–5 wt% for continental eclogite, 1–3 wt% for orthogneiss). Therefore, this study provides integrated geochemical constraints on the source rocks of the post-collisional granites and physicochemical conditions for their genesis. • Post-collisional granites formed at 384–377 Ma are distributed along the North Qaidam orogen • Derived from partial melting of the subducted continental crust at variable crustal levels under different water contents • These granitic rocks have recorded high thermobaric ratios due to post-collisional rifting orogeny [ABSTRACT FROM AUTHOR]

Highlights: [•] The protoliths of the Basongco metamorphic rocks consist mainly of early Paleozoic sedimentary rocks. [•] These rocks experienced the early Mesozoic metamorphism, and associated with the coeval magmatism. [•] The metamorphic conditions are T =640–705°C and P =6.0–8.0kbar. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two fundamental types of collisional orogens have been proposed. • Cold orogens are characterized by brittle fault systems and limited magmatism. • Hot orogens are characterized by ductile flow and widespread partial melting. • MVT Pb–Zn and orogenic gold deposits can occur in both cold and hot orogens. • Porphyry Cu deposits are only associated with hot orogens. It is commonly believed that the thermal regime of collisional orogens evolves from cold to hot with time. Here, we compare the Alpine and Himalayan-Tibetan orogens in terms of their thermal regimes recorded in metamorphic rocks, volcanic suites and related xenoliths, and main mineralization types. The results highlight the fact that the Alpine orogen mostly remained in a relatively cold regime from oceanic subduction to post collision stages. In contrast, most of the Himalayan-Tibetan Plateau rapidly reached and was maintained in a relatively hot regime during the whole course of the collision, except for narrow plate boundary domains. We therefore propose that the thermal regime of collision is inherent to a given geodynamic setting, and that the Alpine and Himalayan-Tibetan orogens represent two fundamental types of collisional orogens, cold and hot, respectively. The main mineral deposit types within collisional orogen include Mississippi Valley type Pb–Zn, orogenic gold, and porphyry Cu deposits. The Mississippi Valley type Pb–Zn and orogenic gold deposits can occur in both cold and hot orogens but porphyry Cu deposits are only associated with hot orogens. Major factors that influence the thermal regime of collisional systems include the rate of continental subduction, the rheology of the underlying lithospheric mantle, the thickness of the overlying lithosphere and radiogenic heat production. Here we propose the removal of suborogenic mantle lithosphere and upwelling of asthenosphere also plays an important role on the thermal structure of collision zones. These processes disturbe the thermal balance of the orogens and cause widespread partial melting of the crust, resulting in the formation of magma-related deposits (i.e., granite-related W-Sn deposits and porphyry Cu deposits). We further give a brief overview of other examples around the globe, such as Pyrenees and Caledonides that reperesent cold orogens versus Variscan and Zagros-Iranian Plateau exemplifying hot orogens. [ABSTRACT FROM AUTHOR]

Late Mesozoic igneous rocks from the north Lhasa block record the Neo-Tethyan orogeny in the southern Tibet Plateau. This study presents geochronological and geochemical data of Bieruozecuo quartz diorite pluton in the northern margin of the Lhasa block to constrain its petrogenesis and tectonic implications. The LA–ICP–MS zircon U–Pb geochronology of quartz diorites shows that the emplacement occurs at ca. 114–116 Ma, belonging to the products of Early Cretaceous magmatic activities. The high concentrations of TiO2, MgO, and MnO, together with SiO2 vs. K2O and A/NK vs. A/CNK diagrams, all suggest that the Bieruozecuo quartz diorites are meta-aluminous and high-potassium calc-alkaline rocks. Their high Sr and low Y and Yb contents, as well as high Sr/Y and La/Yb ratios, are consistent with the typical adakitic rocks. The REE patterns show a large distribution of compositions, which have LREE, while HREE are buffered, along with large ratios of (La/Yb)N, as well as high values of K2O/Na2O, Mg#, Cr, and Ni, all of which imply the partial melting of a delaminated lower crust, without obvious fractional crystallization during the magma ascending and emplacement. This study suggests that, with the closure of the Bangonghu–Nujiang Tethys Ocean Basin, the post-collisional extension of the north Lhasa block will have started no later than ca. 114–116 Ma. Combined with the previous studies, our new data demonstrates that the partial melting of the delaminated lower crust, in a post-collisional setting, may be the main mechanism responsible for the ca. 116–82 Ma adakitic magmatism in the north Lhasa block. [ABSTRACT FROM AUTHOR]

Abstract: The granitic gneisses in the cores of north Himalayan gneiss domes (NHGD) and at the crest of the high Himalayas form part of the greater Himalayan crystalline complex (GHC). These rocks are characterized by the assemblage of quartz, plagioclase, K-feldspar, biotite, muscovite and minor garnet. Here we present results from LA-ICPMS zircon U–Pb dating of six granitic gneiss samples, which reveal formation ages of ca. 500–473Ma and suggest a long-lived magmatism during early Paleozoic in the GHC. Geochemical data show that these rocks are characterized by high SiO2 (70.93–74.59wt.%), K2O (4.22–5.91wt.%), A/CNK values (>1.1) and low Na2O/K2O (0.42–0.83), and enrichment in Rb, Th, U, depletion in Ba, Nb, Ta, Sr, Zr, and strong negative Eu anomalies. These features suggest that the protoliths of the gneisses are high potassium calc-alkaline and peraluminous S-type granites derived from partial melting of crustal materials. The high initial 87Sr/86Sr (>0.706) and negative ε Nd(t) (−6.2 to −10.6) of the granitic gneisses compare with those of the metasedimentary rocks in the GHC, indicating that the granites were generated from partial melting of the sedimentary protoliths. Based on the geochronological, whole-rock geochemical and Sr–Nd isotopic data presented in this study, we suggest that the granites formed in a back-arc setting with a continental arc-affinity related to the subduction of the Proto-Tethyan Oceanic lithosphere. The mafic magmatic underplating, triggered by the subduction, rollback and the break off of Proto-Tethyan Ocean slab, resulted in partial melting of the crust in the GHC. Integrating results from previous studies, we propose an Andean-type orogeny along the margin of the Gondwana. [Copyright &y& Elsevier]

Muscovite 40Ar-39Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: The studied amphibolite-facies metamorphic rocks, typical of the Nyainqentanglha Group, occur as a tectonic block in the central Lhasa terrane, south Tibet, and consist mainly of gneiss, amphibolite, quartz schist and marble. The amphibolite has a similar mineral paragenesis of plagioclase+garnet+biotite+amphibole+quartz±muscovite, and were metamorphosed under P–T conditions of 0.63–0.66GPa and 588–622°C. Zircons from three dated samples include two types. First type of zircons has an inherited magmatic core and a metamorphic rim; whereas the other type of zircons is of metamorphic origin. LA-ICP-MS in situ U–Pb analysis indicates that the inherited magmatic cores of zircons yield widely variable 206Pb/238U ages ranging from 1857Ma to 743Ma, recording the magmatic-thermal events of the material source of the metamorphic rock protoliths. In contrast, the metamorphic zircons yield concordant 206Pb/238U ages of 225–213Ma. The results indicate that the Nyainqentanglha Group has been subjected to Triassic metamorphism, instead of the Precambrian metamorphic basement of the Lhasa terrane as considered traditionally. These rocks, together with the coeval Sumdo eclogite and Pana blueschist, form a Permian to Triassic metamorphic belt with an E–W extension of up to 300km. Therefore, this work provides new constraints on the late Paleozoic to early Mesozoic orogeny in the central Lhasa terrane, south Tibet. [Copyright &y& Elsevier]

Abstract: Charnockites, occurring in the well-studied Gangdese batholith in the southern Lhasa terrane, eastern Himalayan orogen, consist of orthopyroxene, clinopyroxene, plagioclase, and minor quartz and K-feldspar, and show adakitic affinity. Here we present a systematic study on the fluid inclusions in Gangdese charnockites which reveals that the primary fluid inclusions occur isolated or randomly distributed and as trails along intragranular fractures in quartz, and that the secondary ones occur along healed mircofractures and coexist commonly with mineral inclusions of calcite, magnetite and hematite within the host plagioclase and quartz. The fluid inclusions contain dominantly near-pure CO2 with traces of N2. Most of the primary fluid inclusions have low CO2 homogenization temperatures and with densities of 1.138–1.013g/cm3 suggesting trapping pressures of 0.7–1.0GPa at temperatures of 850–950°C. We propose a model in which the southward subduction of Neo-Tethyan mid-oceanic ridge beneath the Lhasa terrane resulted in the release of heat and CO2 from the upwelling asthenosphere through a slab window, providing high-temperatures (HT) and dry CO2-rich fluids for the formation and stabilization of the adakitic charnockite as well as the associated HT granulite-facies metamorphic rocks in the Late Cretaceous, prior to the final collision of the Indian plate with the Asian continent. Our study provides new insights into the geodynamics of Andean-type orogeny in the southern Tibetan Plateau during the Late Mesozoic. [Copyright &y& Elsevier]

Abstract: To better understand Tibetan orogenesis, which involves complex tectonic processes, here we report the first integrated analysis of Hf isotopes of zircon separates and their host rocks from the Transhimalayan batholiths. The rocks studied include 19 granitoids from different parts of the Gangdese batholith, the largest Transhimalayan intrusive complex, and five postcollisional adakites that occurred as plugs or dikes cutting the Gangdese batholith, in the southern Lhasa terrane, southern Tibet. Published zircon Hf isotope data from other Transhimalayan granitoids and the Linzizong volcanic rocks are also synthesized. The magmatic zircons, crystallizing between ca. 200 and 15Ma, show depleted mantle-type Hf isotopic characteristics throughout the Mesozoic but shift markedly in the Paleogene. The Hf isotopic shift is interpreted as tracking the evolving progress of Himalayan sediment subduction driven by the approaching Indian continent, and thus signals the initiation of the India–Asia collision that we infer to have occurred by 55Ma. Our data furthermore indicate that southern Tibet underwent significant crustal thickening during ca. 45 and 30Ma, before emplacement of the postcollisional adakites that exhibit Hf–Nd isotopic systematics suggesting binary mixing of melts from the juvenile Gangdese mafic crust and incorporated Himalayan sediments in the petrogenesis. [Copyright &y& Elsevier]

Abstract: We herein present a new seismic refraction/wide-angle reflection profile that crosses the Songpan–Ganzi terrane, the Animaqing suture zone and the eastern Kunlun mountains (comprised of the South Kunlun and Middle Kunlun blocks separated by the Middle Kunlun fault). The profile is 380km long and extends from Moba to Guide in eastern Tibet. The crustal thickness is about 62km under the Songpan–Ganzi terrane, 62–64km under the South Kunlun, and 60km under the Middle Kunlun block. The Songpan–Ganzi flysch seems to be present up to a depth of 15km south of the Animaqing suture zone, and up to a depth of 10km in the Middle Kunlun block, with thicknesses elsewhere that depend on assumptions about the likely lithologies. The profile exhibits clear lateral variations both in the upper and lower crust, which are indicative of different crustal blocks juxtaposed by the Kunlun fault system. Whether or not the Songpan–Ganzi flysch was originally deposited on oceanic crust, at the longitude of our profile (100°E) it is now underlain by continental crust, and the presence of continental crust beneath the Songpan–Ganzi terrane and of a continental arc under the South Kunlun block suggest Paleozoic continent–continent arc collision in the eastern Kunlun Mountains. Comparison of crustal velocity columns from all wide-angle seismic profiles across the eastern Kunlun mountains indicates a remarkable west-to-east change in the Moho topography across the Kunlun fault system (15–20km Moho step at 95°E, but only 2–5km along our profile at 100°E). Lower-crustal thickness of the Kunlun terranes is rather uniform, about 35km, from 80°–95°E, which suggests that similar thrust-thickening processes have played a role where the Qaidam Basin abuts the Kunlun fault, but thins to 20–25km at 100°E, east of the Qaidam Basin. The increased crustal thickness from 93° to 98°E compared to that at 100°E may be due to the differences in the thickness of the crust of the two plates before their collision, and/or largely achieved by thickening of the lower crust, perhaps indicating a crustal flow mechanism operating more strongly in the western region. [Copyright &y& Elsevier]

Abstract: The Triassic orogeny in North Tibet results from interactions between the South China, North China and Qiangtang (North Tibet) blocks during the closure of the Paleotethys ocean. It is mainly composed, from west to east, by the Bayan Har, Songpan-Garzê, and Yidun (or Litang–Batang) terranes. We focus here on the Triassic Songpan-Garzê fold belt and the actual eastern margin of the Tibetan Plateau which is one of the key areas for understanding the tectonic evolution of the Asian continent and the Tibetan Plateau. At least three major deformation phases are recognized in eastern Tibet and south-east of the South China block: a Neoproterozoic phase (1–0.75Ga) correlated to the assembly and break-up of the Rodinia Continent, a Late Triassic compression event and finally a Tertiary deformation related to the India–Asia collision. The tectonic and geodynamic history of this part of Asia is very complex and often vigorously debated. For example the Triassic compression event in Tibet is usually associated to the Indosinian Orogeny originally defined in Vietnam but this is probably an oversimplification. Our purpose is to review the various models proposed in the literature and to synthesize the tectonic and geodynamic history of this area. We show that the Songpan-Garzê fold belt is not a typical collisional belt: the triangular shape of the closing oceanic basin as well as the huge volume of accreted sediments did not allow a complete continent–continent collision. Finally, the tectonic inheritance plays a major role in the evolution of the eastern margin of Tibet as most of the major Tertiary tectonic structures in the Longmen Shan are reactivated Paleozoic and Mesozoic faults. [Copyright &y& Elsevier]

Abstract: Several classes of geodynamic models have been proposed to explain the evolution of the Himalayan orogen and the Tibetan plateau. Models invoking flow in a weak lower crustal layer have been successful in explaining a number of geological and geophysical observations. Geophysical observations indicate that the weak layer at mid- to lower crustal depths in Tibet may be the result of partial melting. Laboratory studies indicate an order reduction in strength for melt fractions of 5–10%. By relating these laboratory studies to magnetotelluric observations, which are sensitive to the presence of partial melts, it is possible to estimate the flow parameters associated with the channel flow model. Calculations show that in the Central Tibetan Plateau, if a layer consists of partially molten felsic rocks, then conductances in the range 7000–27,000S will produce flow velocities of the order 1cm/a. Beneath the southern part of the Lhasa block and the Qiangtang terrane magnetotelluric studies indicate conductances of up to 20,000S. These conductances suggest effective viscosities of 2.5×1018 to 3×1020 Pas, corresponding to flow velocities between 0.02 and 4.5cm/a. Together with higher pressure gradients near the margins of the plateau these flow parameters clearly support the validity of the channel flow model in these parts of Tibet. Lower crustal conductances (3000S) are reported beneath the northern Lhasa block and deformation by channel flow in this region is unlikely. Assuming a felsic rock composition, the minimum effective viscosity of the crust beneath the northern Lhasa block is estimated as 3×1020 Pas. The corresponding flow velocities do not exceed 0.04cm/a unless higher temperatures than suggested by seismic observations are assumed. [Copyright &y& Elsevier]

Abstract: The Lhasa terrane has long been interpreted as a simple tectonic block rifted from Gondwana during the late Paleozoic and then drifted northward before finally amalgamating with the Qiangtang terrane during the Early Cretaceous. In this paper we document Permian peraluminous granites near Pikang in the southern margin of the central Lhasa terrane, close to the recently documented Songdo eclogite of Permian age. Zircon SHRIMP and LA-ICPMS U–Pb dating for a Pikang granite sample gives an identical crystallization age of about 263 Ma and a wide age range of inherited zircons (283–2141 Ma). In situ Hf isotopic analyses for 20 zircons of 263 Ma yielded ε Hf(t) values of −4.5 to +1.9. The Pikang granites have high A/CNK values (≥1.08) and high normative corundum (1.3–2.0%), indicative of peraluminous S-type granite. They are characterized by moderately negative Eu anomalies (Eu/Eu⁎=0.48–0.61), and strongly negative Ba, Nb, Sr, P and Ti anomalies. The granites have high ε Nd(t) values (−6.4 to −6.0) and low initial 87Sr/86Sr ratios (0.7082–0.7096) relative to melts derived from mature continental crust. These rocks are interpreted to have been generated by mixing between mantle melts and their induced melting of mature crustal materials. We interpret the Pikang peraluminous granite magmatism, the regional angular unconformity between the Middle and the Upper Permian and the eclogite of the same metamorphic age (∼262 Ma) from the same geotectonic location to represent different products of a common event in time and space. We tentatively term this common event as syncollisional orogeny, i.e., “the Permian Gangdese Orogeny”. We further hypothesize that the orogeny may be genetically associated with the collision between the Lhasa terrane and the northern margin of Australia, following the closure of the Paleo-Tethyan Ocean south of the Lhasa terrane. [Copyright &y& Elsevier]

Abstract: Variations in the volume and age of Miocene granites and in mid-crustal conductance from the northwest Himalaya to southeastern Tibet imply lateral differences in late orogenic processes. The change from west to east occurs near the Gurla Mandhata dome, where the Karakoram fault terminates and merges with the Indus–Yarlung suture zone. The ‘channel flow’ model, developed in southeastern Tibet, predicts that anatectic partial melts beneath the Tibetan plateau are gravitationally-driven south to a topographic erosional front and are exposed as leucogranites in the Greater Himalaya Sequence; upwellings of these channel granites occur as gneiss domes in the Tethyan Himalaya Sequence. Published magnetotelluric profiles show high conductivity 30–40 km deep beneath Tibet from c. 400 km north of the Main Frontal thrust south across the suture zone, beneath the Himalayan gneiss domes, and to the topographic front; this conductive middle crust corresponds to 2–4% partial melt in the northwest Himalaya and 5–12% melt in southeastern Tibet, sufficient in the latter case to weaken rock for flow. East of the Karakoram termination leucogranites are abundant and are as young as 7 Ma; west of the termination, channel granites are less abundant and no younger than 18 Ma. Middle Miocene (16–14 Ma) leucogranites are found in the Karakoram fault zone located north of the suture zone and south of the proposed anatectic melt source. The initiation of motion on the crustal-penetrating Karakoram fault at 25–21 Ma may have created a barrier to the southward flow of mid-crustal melts and acted as a vertical conduit for these same melts. [Copyright &y& Elsevier]

Abstract: The Triassic fold belt of North Tibet is mainly composed, from west to east, of the Bayan Har, Songpan–Garzê, and Yidun (or Litang–Batang) terranes. The Indosinian orogeny results from interactions between the South China, North China and Qiangtang (North Tibet) blocks during the closure of the Palaeotethys. A synthesis of the tectonic and geochronological data available on this belt is presented and a new geodynamic model of its formation is proposed. At the end of the Permian, a synchronous activity along three subduction zones, Kunlun–Anyemaqen to the north, Jinsha to the south and Yushu–Batang to the east, induced the growth of wide accretionary orogens until the end of the Triassic period. The onset of subduction in Tibet is contemporaneous with Indosinian tectonism in Indochina (pre-Norian). However, the main tectonic events that lead to the closure of the Tethysian basin and the subsequent building of the Triassic belts are younger (220–200Ma). [Copyright &y& Elsevier]

Structural style along the active, NW-striking, right-slip Karakoram fault in western Tibet ranges from transpression in the north (37° to 34°N) to transtension in the south (34° to 32°N). This transition in structural style occurs at a 27-km-wide bend in the fault. Our new neotectonic mapping has documented the long-asserted structural linkage between the ENE-striking Gozha–Longmu Co fault system and the similarly oriented active, leftslip Altyn Tagh fault to the northeast. This mapping also indicated that the restraining bend in the Karakoram fault is located where this fault intersects the Gozha-Longmu Co extension of the Altyn Tagh fault to the west. Additional observations from remotely sensed imagery suggest that the total left-separation along the Gozha-Longmu Co fault system is 25-32 km. We use the new neotectonic mapping and published slip rates to develop a simple kinematic model for the main active faults in western Tibet to explore the genetic relationship between slip along the Gozha- Longmu Co fault system and the geometric and kinematic evolution of the Karakoram fault. This model combines published geodetic and Quaternary slip rates with the known fault geometries and demonstrates that the transition from transpression to transtension along the Karakoram fault can be explained by differential motions between the NW Himalaya, the Tianshuihai terrane, and the Tibetan Plateau. These motions produce bending and transtension along the central and southern Karakoram, respectively, and movement of the Tibetan Plateau at a rate of 6–13 mm/ yr toward the east-southeast relative to the Pamirs. We also fi nd that the Gozha–Longmu Co fault system likely initiated between 10 and 3 Ma to accumulate 25–32 km of total left separation. We suggest that the Gozha-Longmu Co fault system formed during late Miocene to Pliocene structural reorganization of the southwestern Altyn Tagh and southern Karakoram fault systems to allow eastward migration of the Tibetan Plateau and northward migration of the Pamir syntaxis. [ABSTRACT FROM AUTHOR]