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Deciphering the exhumation mechanism of high-pressure−low-temperature (HP-LT) metamorphic rocks can provide important insights into the tectonic evolution of oceanic subduction zones at active continental margins. Here, we present a multidisciplinary study examining the exhumation tectonics of the Permo−Triassic eclogite-bearing HP-LT terranes of the Central Qiangtang metamorphic belt (CQMB) in the central Tibetan Plateau. Field geological relations and microscopic observations show that the HP-LT rocks in the Lanling area are separated from the epimetamorphic late Paleozoic ophiolite mélange of the hanging wall by low-angle detachment faults and primarily exhibit five stages of deformation. The HP-LT terranes were exhumed as a metamorphic core complex and show pervasive synexhumation top-to-the-SW and -S shear structures. The results of the petrological and mineralogical analysis and pseudosection modeling of retrograde eclogites indicate that these rocks are characterized by synexhumation mineral growth pulses with hairpin-type decompressional pressure-temperature trajectories. A compilation of previous geochronological data and our 40Ar/39Ar dating results of synexhumation minerals and shear bands in HP-LT rocks indicate continuous exhumation at ca. 244−215 Ma prior to the continental collision between the North Qiangtang Block (NQB) and South Qiangtang Block. Moreover, the CQMB is likely an autochthonous accretionary wedge resulting from northward subduction of the Paleo-Tethys Ocean beneath the NQB. Combined with ca. 243−230 Ma mantle upwelling to the north of Lanling, we infer that the CQMB, namely, the accretionary wedge of the Paleo-Tethys Ocean, experienced Middle−Late Triassic lithospheric extension in the NW-SE direction.

The analysis of folds within pebbles in conglomerates has been used to infer deformation events before deposition of the conglomerate. However, it is not clear whether folds can develop within pebbles during subsequent conglomerate deformation. We use numerical modelling to investigate folding within internally layered pebbles in a ductile deformation regime and simple shear deformation. We vary the initial orientation and rheology of the layers within pebbles, as well as the relative rheology of the conglomerate matrix, for single isolated pebbles and multiple interacting pebbles. We use a power-law viscous rheology for both the pebbles and their matrix. Folding within pebbles can indeed occur, but only within a narrow range of initial layer orientations, strength or viscosity ratio between the internal layers and that of the matrix relative to the pebble layers. Results are used to interpret the strongly deformed conglomerates from the Proterozoic Hutuo Group in the Wutai Mountains, North China Craton, that contain a small percentage of pebbles with internal folds. Based on field observations and numerical modelling results, we suggest that these formed during deformation of the conglomerate and do not represent inclusion of previously folded lithologies into the unit., Fieldwork by HR in the Wutai Mountains area, China was supported by the China Geological Survey (grant No. 12120114076401). Fieldwork by PDB was kindly supported by the Chinese University of Geosciences (Beijing). We appreciate the help for the fieldwork from Zhongbao Zhao, Changshun Wen, Chao Li and the constructive suggestions from Guoli Yuan and Zhongbao Zhao. HR thanks the financially support by the China Scholarship Council (CSC; No. 201506400014) and the China Geological Survey (grant No. DD20190465). EGR acknowledges funding by the Spanish Ministry of Science, Innovation and Universities (“Ramón y Cajal” fellowship RYC2018-026335-I). M.-G.L acknowledges the support of the Juan de la Cierva programme of the Government of Spain's Ministry for Science, Innovation and Universities (grants FJCI-2015-2417 and IJC2018-036826-I).

[The late Permian–Triassic trench‐slope basin in the CQMB showing the correlation between spatiotemporal variations in basin sedimentation and the extensional tectonism of the accretionary wedge. , Abstract Records of sedimentation and deformation in trench‐slope basins contain valuable tectonic information about the associated oceanic subduction zone. Here, we present a multidisciplinary study on newly discovered late Permian–Triassic sedimentary successions in the >500‐km‐long Central Qiangtang metamorphic belt (CQMB) to better understand the type of basin and the concomitant tectonism. The Mayer Kangri succession contains lithofacies associations of submarine fan siliciclastic rocks, slope‐environment limestone, deep marine chert and minor olistostromes from the forearc basin. The conodont assemblages and sandstone and andesite interlayers yield continuous stratigraphic ages from the Lopingian to middle Norian. The clastic sediments had two provenances, including the epicontinental arc in the North Qiangtang block (NQB) and synchronous volcanism in the accretionary wedge. Moreover, a large suite of the Anisian–early Carnian radiolarian cherts (>30 m thick) was discovered in the Lanling area. Regionally, the CQMB shows evident spatiotemporal variations in late Permian–Triassic sedimentation, with a general depositional trend of southward deepening and getting younger. The three identified subzones include a bathyal setting, a carbonate platform setting and a deep marine setting from north to south. These observations indicate that the late Permian–Triassic sedimentary successions in the CQMB were deposited in a trench‐slope basin environment during the northward subduction of the Longmu Co–Shuanghu Tethys Ocean beneath the NQB. Generally, the CQMB and the concomitant trench‐slope basin is among the well‐preserved ancient analogs characterized by extensional tectonism. The syndepositional horst‐graben‐like structure, forearc basin‐derived olistostromes, abyssal radiolarian cherts and synchronous volcanism provide new implications for the geological evolution of the trench‐slope basin.]

Many large and super-large copper deposits have been discovered and explored in the Tibet Plateau, which makes it the most important copper resource reserve and development base in China. Based on the work of the research team, the paper summarizes the geological characteristics of the main copper deposits in Tibet and puts forward a further prospecting direction. A series of large accumulated metal deposits or ore districts from subduction of Tethys oceanic crust to India-Asia collisionhave been discovered, such as Duolong Cu (Au) ore district and Jiama copper polymetallic deposit. The ore deposits in the Duolong ore district are located in the lowstand domain, the top of lowstand domain, and the highstand domain of the same magmatic-hydrothermal metallogenic system, and their relative positions are the indicators for related deposits in the Bangong Co-Nujiang metallogenic belt. The polycentric metallogenic model of the Jiama copper polymetallic deposit is an important inspiration for the exploration of the porphyry mineralization related to collision orogeny. Further mineral exploration in the Tibet Plateau should be focused on the continental volcanic rocks related to porphyry-epithermal deposits, orogenic gold deposits, hydrothermal Pb-Zn deposits related to nappe structures, skarn Cu (Au) and polymetallic deposits, and the Miocene W-Sn polymetallic deposits. ©2021 China Geology Editorial Office.

Abundant Early Cretaceous magmatism is conserved in the central and southern Great Xing’an Range (GXR) and has significant geodynamic implications for the study of the Late Mesozoic tectonic framework of northeast China. In this study, we provide new high-precision U–Pb zircon geochronology, whole-rock geochemistry, and zircon Hf isotopic data for representative intrusive rocks from the northern part of the Ulanhot area to illustrate the petrogenesis types and magma source of these rocks and evaluate the tectonic setting of the central-southern GXR. Laser ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon U–Pb dating showed that magmatism in the Ulanhot area (monzonite porphyry: 128.07 ± 0.62 Ma, quartz monzonite porphyry: 127.47 ± 0.36, quartz porphyry: 124.85 ± 0.34, and granite porphyry: 124.15 ± 0.31 Ma) occurred during the Early Cretaceous. Geochemically, monzonite porphyry belongs to the metaluminous and alkaline series rocks and is characterized by high Al2O3 (average 17.74 wt.%) and TiO2 (average 0.88 wt.%) and low Ni (average 4.63 ppm), Cr (average 6.69 ppm), Mg# (average 31.11), Y (average 15.16 ppm), and Yb (average 1.62 ppm) content with enrichment in Ba, K, Pb, Sr, Zr, and Hf and depletion in Ti, Nb, and Ta. The granitic rocks (e.g., quartz monzonite porphyry, quartz porphyry, and granite porphyry) pertain to the category of high-K calc-alkaline rocks and are characterized by high SiO2 content (>66 wt.%) and low MgO (average 0.69 wt.%), Mg# (average 31.49 ppm), Ni (average 2.78 ppm), and Cr (average 8.10 ppm) content, showing an affinity to I-type granite accompanied by Nb, Ta, P, and Ti depletion and negative Eu anomalies (δEu = 0.57–0.96; average 0.82). The Hf isotopic data suggest that these rocks were the product of the partial melting of juvenile crustal rocks. Notably, fractionation crystallization plays a crucial role in the process of magma emplacement. Combining our study with published ones, we proposed that the Early Cretaceous intrusive rocks in the Ulanhot area were formed in an extensional tectonic background and compactly related to the subduction of the Paleo-Pacific Ocean plate.

Latest Permian to Triassic plutons are widespread in the northern North China Craton (NCC); most of them show calc-alkaline, high-K calc-alkaline, or alkaline geochemical features. The Shadegai pluton in the Wulashan area has shoshonitic affinity and I-type character, and is composed of syenogranites containing abundant mafic microgranular enclaves (MMEs). LA-MC-ICP-MS U–Pb data yield weighted mean 206Pb/238U ages of 222 ± 1 Ma and 221 ± 1 Ma for the syenogranites and MMEs, respectively, suggesting their coeval formation during the Late Triassic. The syenogranites have high SiO2 (70.42–72.30 wt.%), K2O (4.58–5.22 wt.%) and Na2O (4.19–4.43 wt.%) contents but lower concentrations of P2O5 (0.073–0.096 wt.%) and TiO2 (0.27–0.37 wt.%), and are categorized as I-type granites, rather than A-type granites, as previously thought. These syenogranites exhibit lower (87Sr/86Sr)i ratios (0.70532–0.70547) and strongly negative whole-rock εNd(t) values (–12.54 to –11.86) and zircon εHf(t) values (–17.81 to –10.77), as well as old Nd (1962–2017 Ma) and Hf (2023–2092 Ma) model ages, indicating that they were derived from the lower crust. Field and petrological observations reveal that the MMEs within the pluton probably represent magmatic globules commingled with their host magmas. Geochemically, these MMEs have low SiO2 (53.46–55.91 wt.%) but high FeOt (7.27–8.79 wt.%) contents. They are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). They have whole-rock (87Sr/86Sr)i ratios varying from 0.70551 to 0.70564, εNd(t) values of −10.63 to −9.82, and zircon εHf(t) values of −9.89 to 0.19. Their geochemical and isotopic features indicate that they were derived from the subcontinental lithospheric mantle mainly metasomatized by slab-derived fluids, with minor involvement of melts generated from the ascending asthenospheric mantle. Petrology integrated with elemental and isotopic geochemistry suggest that the Shadegai pluton was produced by crust-mantle interactions, i.e., partial melting of the lower continental crust induced by underplating of mantle-derived mafic magmas (including the subcontinental lithospheric mantle and asthenospheric mantle), and subsequent mixing of the mantle- and crust-derived magmas. In combination with existing geological data, it is inferred that the Shadegai pluton formed in a post-collisional extensional regime related to lithospheric delamination following the collision between the NCC and Mongolia arc terranes. Keywords: Magma mixing, Crust-mantle interaction, Lithospheric delamination, Post-collision, North China Craton

Deciphering the exhumation mechanism of high-pressure, low-temperature (HP-LT) metamorphic rocks can provide important insights into the tectonic evolution of oceanic subduction zones at active continental margins. Here we present a multidisciplinary study examining the exhumation tectonics of the Permo–Triassic eclogite-bearing Lanling HP-LT terrane within the Central Qiangtang metamorphic belt (CQMB). Field relations and microscopic observations show that the HP-LT rocks are separated from the Permian ophiolite mélange of the hanging wall by low-angle detachments and exhibit five stages of deformation. The pervasive top-to-the-SW and -S shearing structures imply that the Lanling HP-LT terrane was exhumed as a transtensional metamorphic core complex (mcc). The results of the petrological and mineralogical analysis and pseudosection modeling of eclogites indicate that the eclogites and blueschists are characterized by synexhumation mineral growth pulses with decompressional P-T trajectories. A compilation of previous geochronological data and our 40Ar/39Ar dating results of shearing structures in HP-LT rocks indicate a continuous exhumation at ca. 244–210 Ma. Moreover, the CQMB experienced lithospheric transtension, as shown by the Middle–Late Triassic geological events, which include mantle upwelling at ca. 237–230 Ma and abyssal basin development in the Anisian–middle Norian. These observations indicate that the CQMB is likely a autochthonous accretionary wedge resulting from northward subduction of the Paleo-Tethys Ocean beneath the North Qiangtang Block (NQB). Moreover, the transtension of the CQMB occurred in the late stage of the oceanic subduction, which was probably triggered by oceanic slab rollback.

Our field work was supported by the Young Scientist Fund of the National Natural Science Foundation of China (Grant 41402177). The experimental items were financially supported by the China Geological Survey (CGS): “1:50,000 regional geological surveys in the Gangmari area of Tibet” (Grant 1212011086062) and the Ministry of Education of the People's Republic of China (Grant 649199111027).

Conglomerates have been widely used to investigate deformation history and rheology, strain, vorticity and viscosity. Previous studies reveal that several factors, such as pebble shapes and concentrations, as well as material properties, affect conglomerate deformation. However, how pebble concentration and interaction between pebbles affect deformation is not understood very well. We use the 2D numerical modelling platform ELLE coupled to the full field crystal visco-plasticity code (VPFFT) to simulate the deformation of conglomerates with various viscosity contrasts between pebbles and matrix and different pebble concentrations, with both linear (stress exponent n = 1) and power-law (n = 3) viscous rheologies, under simple shear conditions up to a shear strain of ten. Pebbles can behave as effectively passive, deformable or effectively rigid. An increase in pebble concentrations/viscosity contrasts enhances pebble deformation, but reduces their rotation. A mean aspect ratio (Rf) - orientation (ϕ) plot is proposed to gain an estimate of pebble deformation behaviour and the amount of bulk strain. Closely spaced rigid or deformable pebbles can form clusters that mechanically act as single inclusions. Rigid clusters rotate and survive for only short strain increments, whereas the more stable deformable ones keep on elongating with minor rotation. We provide a natural example of deformed conglomerates from the Wutai Mountains, North China Craton. These consist of banded-iron-formation (BIF) pebbles embedded in a schistose matrix. Using the mean Rf-ϕ plot, a finite strain of ∼6 under simple shear could be determined. The viscosity of the pebbles is estimated at about 5–8 times that of the matrix for a linear rheology (n = 1), or 2 to 5 times if a power-law rheology with n = 3 is assumed.

The recently discovered Diyanmiao ophiolite in the eastern part of the Erenhot-Hegenshan ophiolite belt forms part of the southeastern domain of the Central Asian Orogenic Belt (CAOB). The ophiolite suite is composed of the northern Baiyinbulage ophiolite and the southern Naolaiketu ophiolite, each extending for nearly 100 km, and a width of around 6 km. The suite preserves a well-exposed and a nearly-complete ophiolite stratigraphy, and includes, from bottom to top, harzburgite, bedded gabbro, isotropic gabbros, anorthosite, spilite, pillow basalt, keratophyre, baschtauite, with overlying chert, and plagiogranite veins locally intruding the pillow basalt and gabbro. The pillow basalts possess the geochemical characteristics of Hahajima island arc tholeiite (IAT), indicating that the Diyanmiao ophiolite formed in the incipient arc setting of the supra-subduction zone. LA-ICP-MS U-Pb dating of zircon grains from three gabbro samples yield ages of 361 ± 13 Ma, 356.7 ± 3.8 Ma and 340 ± 14 Ma, indicating an early-Carboniferous age for the Diyanmiao ophiolite. We suggest that the intra-oceanic subduction initiation of the Erenhot-Hegenshan paleo-ocean during the Early Carboniferous resulted in the formation of an incipient arc oceanic crust, and that the Diyanmiao ophiolite represents an important north-dipping subduction event of the paleo Asian oceanic crust beneath the southern margin of the Siberian Plate after Early Carboniferous and Early Permian. Our study provides further insights into the evolution of the Paleo-Asian Ocean and eventual construction of CAOB, the globe's largest Phanerozoic orogen.

In the background region of the Tibetan Plateau (TP), the rapid urbanization probably results in the massive generation of persistent organic pollutants (POPs), which lacks monitoring and evaluation. Since landfill could serve as an important sink of the locally used POPs, the analysis of POPs in the Tibetan landfill area might help us to understand the source composition and their transport in the TP. In this study, the concentration variations of polybrominated diphenyl ethers (PBDEs) in five soil profiles and seven surficial sediments around the largest Tibetan landfill were investigated. The total concentrations of PBDEs ranged from 128 to 1219 ng/kg in soils, and from 447 to 7295 ng/kg in sediments. The dominance of nona- and deca-BDEs possibly indicated the wide usage of deca-BDE as flame retardant in the TP. The vertical and spatial distribution patterns of PBDEs within soils plausibly revealed their main transport pathways by atmospheric dispersion and leachate seepage from landfill. Based on principal components analysis and multiple linear regression, these two pathways were estimated to account for 61% and 39% of the total concentrations, respectively. Additionally, the spatial and vertical distributions of octa-to deca-BDEs within soils were significantly influenced by soil particle size. Although the PBDEs inventory in the study area was comparatively low, the rapid urbanization in the TP might dramatically accelerate the PBDE emissions in the future. This study firstly introduced the presence of local PBDEs in the TP, and the inventory already influenced the surrounding environment. Once involved in the regional cycle of the TP, the local source of PBDEs from waste might significantly serve to raise background level resulting otherwise primarily from long-range atmospheric transport.

The sedimentary core in remote alpine lakes has been recognized as an ideal proxy to reconstruct the emission and air deposition histories of persistent organic pollutants (POPs). Nevertheless, POPs formerly stored in a catchment might also contribute to the variation in the lake sediment by lateral remobilization. In this study, to reveal the relative importance of lateral remobilization, we measured the vertical profiles and isomeric ratios of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs) and endosulfan in a dated sedimentary core collected from Lake Yamzho Yumco in the southern Tibetan Plateau. In addition to the flux peaks in the 1970s corresponding to the heavy atmospheric deposition of DDTs and HCHs, these pollutants’ fluxes displayed rebounds in the flood periods, with characteristic low ratios of DDT/DDE (α-/β-HCH). This might indicate a massive remobilization of “weathered” pesticides from catchment soil to the lake because of strong hydro-dynamics. Moreover, the relative contribution of lateral remobilization to the lake sediment in the past decades was recognized through the correlation between DDT/DDE (α-/β-HCH) ratios and ∑DDT (∑HCH) fluxes. The results showed that the lateral remobilization contributed to 20–42% of the total fluxes. This study discriminated the air deposition from the contribution of lateral remobilization, which improves current understanding of the vertical POPs profiles in the sedimentary core.

Sediment cores from lakes have been used to reconstruct the historic deposition of persistent organic pollutants (POPs), especially in remote alpine areas. To reconstruct the deposition history of organochlorine pesticides (OCPs) in the Tibetan Plateau (TP), two sediment cores from Yamzho Yumco Lake were drilled and dated with high-resolution, from which 23 OCPs were analyzed in greater detail. Regarding several legacy compounds, concentration peaks in the cores were observed in the 1970s, corresponding to the heavy usage of these compounds around the world. In addition, another peak was found at the end of the 1990s, which was explained as the addition of OCPs released from melting glaciers or the cryosphere due to global warming. Furthermore, it was found that the transformation or degradation of OCPs after deposition in the lake was limited by comparing the values of isomeric ratios at different times, such as (DDD+DDE)/∑DDTs, o,p'-DDT/p,p'-DDT and β-HCH/∑HCHs. Such results ensure that the detected OCPs in the lake sediments really reflect their characteristics at the time of deposition. On the other hand, weak environmental self-purification of the OCPs made them last longer in the TP than in other regions. Reasonably, the fragile ecological environment of the TP would be threatened not only by legacy POPs that remain in the sediments and soils but also by POPs released from melting glaciers or the cryosphere in the next few decades under the influence of global warming. Our research provides an insight into the influence of global warming and glacial melting on the environment of the TP, and further work to gain a better understanding of the environmental processes of POPs in the TP is ongoing.

The Tethys Himalaya sedimentary sequence (THS) is characterized by N–S trending extensional rifts (NSTR) and the North Himalayan gneiss domes (NHGD). The Cuonadong dome, as one of the NHGD, is located at the N–S trending Cuona rift in the eastern part of the Tethys Himalaya. The dome had undergone four major deformation events: D1, characterized by top-to-S thrust resulting in N–S shortening and vertical thickening; D2, characterized by vertical thinning and N–S extensional deformation; D3, approximately E–W extensional deformation associated with intrusion of leucogranites; and D4, late collapse structural deformation around the core of the Cuonadong dome. There are numerous granitic dykes at the contact zone between the granite and surrounding rocks in the middle unit of the Cuonadong dome. Field observations show that granite intrusion occurred in part synchronously with D3, E–W extensional deformation. U–Pb–zircon dating shows that the granite crystallization took place at ca. 17.5–15.6 Ma, while muscovite Ar–Ar geochronological data from the deformed pegmatite and mylonitic schist in the Cuonadong dome show that the onset of the E–W extensional deformation is between 16.5 and 14.8 Ma, and suggesting that granite intrusion was synchronous with the E–W ductile extensional deformation in the Cuonadong dome, southern Tibet. Combined with previously published ages of the South Tibetan Detachment System (STDS), our study shows that granite intrusion was at least locally contemporaneous with both the E–W and N–S extensional deformation, especially with the E–W extension.

The timing of the closure of the Bangong Ocean between the Lhasa and South Qiangtang Terranes in central Tibet and the resulting crustal thickening are still under debate. We integrate published apatite fission track and (U–Th)/He thermochronometer data with new zircon (U–Th)/He ages from eight samples and with structural profiles to document that the South Qiangtang Terrane experienced slow exhumation between 200 and 150 Ma, associated with the opening of the Bangong Ocean. Accelerated exhumation (around 0.2–0.3 mm/a) of the South Qiangtang Terrane was initiated at around 150 Ma. This exhumation event is interpreted to reflect collision between the Lhasa and South Qiangtang Terranes after closure of the Bangong Ocean, associated with crustal thickening via thick-skinned folding and thrusting within the South Qiangtang Terrane. The amalgamation of the Lhasa and South Qiangtang Terranes recorded here may represent the first stage of crustal thickening in the central Tibetan Plateau. This article is protected by copyright. All rights reserved.

The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic–early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P–T data, and Ar–Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E–W-trending, ~2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist melange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying melange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and ~404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at ~0.7–1.1 GPa and ~400 °C. Our Ar–Ar dating of amphibole reveals rim-ward decreasing in age bands, including ~242.4–241.2 Ma, ≥202.6–196.8, and 192.9–189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang (~244–220 Ma); (2) syn-collisional slab-break off (223–202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth (~202.6–197 Ma); and (4) post-collision contraction and reburial (195.6–188.7 Ma).

Upper Triassic reef corals from the Riganpeicuo Formation in northern Tibet represent important scleractinian coral fauna that help explain the palaeobiogeography of the eastern Tethys region during the Late Triassic period. The corals were discovered in bedded limestone in patch reefs or biostromes of the Renacuo area. In this paper, 15 genera and 25 species are identified and categorized, the systematic composition of these corals and their relationships with other Triassic coral faunas are also discussed. The results show that these corals are composed of the typical elements of the western Tethys, with the following genera and species that are endemic to China: Radiophyllia cf. astylatus, Margarosmilia zogangensis and Conophyllopsis qamdoensis, and the genera Retiophyllia, Margarosmilia, Hydrasmilia, Procyclolites, Pamiroseris, Araiophyllum, Stylophyllopsis, Stylophyllum and Guembelastraea provide important links to the Tethys province. The coral fauna also highlights the connection between the Qiangtang terrane and the Songpan-Ganzi fold belt, but shows that the areas are distinct from the Himalayan terrane. It has been interpreted that the Qiangtang terrane and the Songpan-Ganzi fold belt were in the vicinity of the gradually-closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms of these areas. On the other hand, the Himalayan terrane was separated from the Qiangtang terrane by a wide ocean–meso Tethys during the Late Triassic period, which made it impossible for the benthonic organisms on both flanks to freely migrate toward the opposite continental margins.

This work was jointly funded by the Young Scientist Fund of the National Natural Science Foundation of China (grant 41402177) and the Fundamental Research Funds for the Central Universities (2652014004). Our field work was supported by a project issued by the China Geological Survey (CGS): The integrated geological survey on the west part and central uplift of Qiangtang Block (grant 12120115026901).

Glacier alluvial deposits record persistent organic pollutants (POPs) not only derived from the atmospheric deposition but also from the release of glacial melting. The evidence for melting glacier in the Tibetan Plateau (TP) as a secondary source of pollutants is introduced through investigating the concentration of organochlorine pesticides (OCPs) in four deposited profiles collected at the edge of the Changwengluozha glacier. Two concentration peaks were observed for dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) in the past century. The first peak was observed in the 1970s, corresponding with the heavy usage of HCHs and DDTs in the surrounding countries and regions. The second one was in 2000 when the production and usage of DDTs and HCHs were strictly limited, which possibly indicated a significant release from melting glacier. This result was further supported by the enantiomeric fraction values for α -HCH and o,p ′-DDT. On the other hand, the dramatic increase of polycyclic aromatic hydrocarbons (PAHs) from atmospheric deposition, which was associated with the socioeconomic development in Tibet, shaded the release of PAHs from melting glacier. This study reveals not only the air deposition history of legacy POPs but also a substantial release of OCPs from glacier to the adjacent environment. Our research supports the hypothesis that the melting glacier in the TP represents a secondary source of OCPs, which is consistent with the findings in the Alps glaciers.

The Cuonadong super-large Be-W-Sn rare metals deposits are hosted by skarns and marbles in the middle unit of the Cuonadong Dome. Rocks in the Cuonadong Dome record four major deformational events: D1, top-to-S thrust; D2, top-to-N extension; D3, approximately E–W extensional deformation; and D4, late collapse structural deformation. Skarns and/or marbles featured by the directional alignment of skarn minerals are exposed in garnet-staurolite-bearing mica schist, and are closely related to the deformed leucogranites and pegmatites. The boundary between leucogranites and skarns is locally gradual or sharp, which suggests that skarns and the deformed leucogranites resulted from the synkinematic magmatism and the strong activity of the STDS. Ar-Ar dating of muscovite from the deformed granites in the middle unit and biotite from granitic gneiss in the core yielded Ar-Ar plateau ages of 15.0 ± 0.2 Ma and 13.9 ± 0.4 Ma, respectively, which reflects the age of syntectonic magmatism, and the activity time of the STDS at the Cuonadong Dome, respectively. Ar-Ar dating of biotite from marble in the middle unit yielded Ar-Ar plateau age of 16.1 ± 0.2 Ma, which was interpreted as the formation age of the synkinematic skarns. Skarns in the Cuonadong Dome were related to the detachments and formed in association with the emplacement of leucogranites. Therefore, we suggest that the formation of the Cuonadong Be-W-Sn skarn deposit was contemporaneous with the intrusion of leucogranitic magma and the top-to-north extensional deformation along the STDS.

Zircon LA-MC-ICP-MS U–Pb geochronology, major and trace element geochemistry, and Sr–Nd–Pb–Hf isotope analysis were performed on the Paleoproterozoic mafic dykes from the Wulashan area to investigate their petrogenesis and tectonic implications. The mafic dykes are diabase porphyries with a dominant mineral assemblage of plagioclase and clinopyroxene. Zircon U–Pb isotopic data yield weighted mean 207Pb/206Pb ages of 1769 ± 12 and 1770 ± 5 Ma for the NEE–EW trending and the N–S trending mafic dykes, respectively. Geochemically, these rocks belong to medium-K or high-K calc-alkaline series with K2O + Na2O contents of 3.39 to 5.28 wt.%. They show low MgO contents (3.92–4.63 wt.%) and Mg# values (32–37) and high contents of TiO2 (2.38–3.23 wt.%) and FeOt (13.60–15.29 wt.%). The dykes exhibit right-declined REE patterns, with (La/Yb)N of 4.63–9.35 and LREE/HREE of 5.02–7.92, and are characterized by enrichment in Rb, Ba, K, La, and Ce but depletion in Nb, Ta, Th, U, and Sr. Particularly, the NEE–EW trending samples display pronounced positive Ti anomalies, whereas the N–S trending samples exhibit negative P anomalies. All of the studied mafic dykes display similar Nd–Pb–Hf isotopic compositions with eNd(t) ranging from −3.41 to −1.49, (206Pb/204Pb)i of 15.0010 to 16.6626, (207Pb/204Pb)i of 15.2192 to 15.3468, (208Pb/204Pb)i of 35.0147 to 37.2389, and zircon eHf(t) values varying from −2.8 to 3.8. Geochemical modeling reveals that the NEE–EW and N–S trending mafic dykes were derived from 8% to 10% and 2%–4% partial melting of a common mantle source with ∼2% garnet. During emplacement, the parental mafic magma of the NEE–EW trending dykes experienced fractionation of clinopyroxene and accumulation of Ti–Fe oxides, whereas the N–S trending ones experienced fractionation of olivine and apatite. The selective enrichment of LILEs and LREEs, together with negative eNd(t) values and EMI-like Pb isotopic compositions, suggests that the dykes were derived from the partial melting of subcontinental lithospheric mantle metasomatized by slab-derived fluids. Furthermore, the marked depletion in Th and U and decoupled Nd–Hf isotopes indicate the incorporation of continental crustal components into the mantle prior to partial melting. Based on the geochemical features and previous regional geological data, we propose an extensional tectonic setting for the formation of the mafic dykes from the Wulashan area, possibly related to the post-orogenic setting following the collision between the Yinshan and Ordos Blocks.