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It is well established that Indian- and Pacific-type mantle domains observed in the present-day upper mantle are both long-lived and can be traced back to at least the Early Paleozoic, with their contrasting isotopic compositions inherited from mantle beneath the Tethys and Panthalassic oceans, respectively. But, the long-term evolution of the Tethyan-Indian oceanic mantle remains loosely constrained due to sparse sampling of the Tethyan oceanic lithosphere, which makes it unclear if there has been temporal variation of its diagnostic DUPAL anomaly throughout the Phanerozoic, and what caused any changes. To address these issues, we report new geochemical data, including bulk-rock major and trace elements and Sr-Nd-Hf-Pb isotopes, for samples from Tethyan ophiolites located in the Tibetan Plateau. These results, combined with existing data for ophiolites across the Tethyan domain and Indian oceanic crust, demonstrate that the DUPAL anomaly in the Tethyan-Indian oceanic mantle is long-lasting, but its strength is weakening through time. The DUPAL anomaly in the Tethyan-Indian upper mantle was most pronounced in the Paleozoic with a homogeneous Indian-type asthenosphere underlying the Proto/Paleo-Tethys oceans, but has become less obvious since the Mesozoic with an isotopically heterogeneous asthenosphere beneath the Neo-Tethys and Indian oceans containing Pacific-type mantle fragments. We propose that the declining DUPAL anomaly in the Tethyan-Indian oceanic mantle since the Mesozoic was most likely associated with inflow of Pacific-type mantle during breakup of Pangea and Gondwana, when interaction between Indian- and Pacific-type mantle was more efficient. On the other hand, Indian-type asthenosphere might have been squeezed out into the Panthalassic-Pacific oceanic mantle during closure of the Tethys Ocean. This transfer may have contributed, at least in part, to the DUPAL isotopic anomaly detected in the Panthalassic-Pacific oceanic mantle. Our findings indicate that tectonically-induced asthenospheric flow permits interactions between Indian- and Pacific-type mantle domains and contributes to evolving mantle compositions. [ABSTRACT FROM AUTHOR]

Intra-oceanic arcs are one of the major building blocks of continents, and the rarely exposed calc-alkaline plutons in intra-oceanic arcs are a critical component of arc crust. These calc-alkaline plutons provide juvenile crustal materials to the continental crust, and thus their petrogenesis has important implications for the formation and evolution of continental crust. Here, we present the results of an integrated study, involving field investigation, petrology, geochronology and geochemistry, on calc-alkaline intermediate–felsic plutons and their mafic magmatic enclaves (MMEs) within a Proto-Tethyan intra-oceanic arc in the Lajishan terrane of the Qilian Orogen, northern Tibetan Plateau. These calc-alkaline intermediate–felsic plutons range from gabbroic diorites, through diorites, to granodiorites. In situ zircon U–Pb dating demonstrates that these plutons were emplaced in the Early Paleozoic (474–460 Ma), slightly older than previously identified 460–440 Ma intra-oceanic arc volcanics (boninites, ankaramites, high-Mg basaltic andesites, high-Al andesites, sanukites) in the Lajishan terrane. The geochemistry of these plutons indicates that they were differentiation products of subduction-metasomatized arc mantle-derived melts, and isotope modeling constrains that their mantle source was metasomatized by less than 10% addition of slab-derived fluids/melts. Their parental melts experienced polybaric medium- to high-pressure fractional crystallization to generate the compositional variation of these plutons. There are two types of MMEs according to their different geochemistry (high- and low-MgO MMEs) and both of them are early crystallized melts derived from the heterogeneous subduction-metasomatized arc mantle wedge, captured by evolving magmas. Alkaline high-MgO MMEs represent near-primitive alkaline melts derived from melting of pyroxenite with phlogopite-enriched veins in the heterogeneous arc mantle wedge, while low-MgO MMEs stand for relatively evolved calc-alkaline melts formed during differentiation of the melts parental to their host. The upper crustal construction of this Proto-Tethyan intra-oceanic arc was achieved through earlier emplacement of 474–460 Ma calc-alkaline plutons followed by slightly later eruption of arc volcanics at 460–440 Ma above these plutons. As approximated by the composition of these calc-alkaline plutons and arc volcanics, the upper crustal composition of this Proto-Tethyan intra-oceanic arc is still juvenile and primitive. This juvenile intra-oceanic crust was accreted to continental blocks through arc–continent collision at 440–420 Ma, in response to closure of the Proto-Tethys Ocean. The accreted intra-oceanic crust represents addition of juvenile crustal materials to existing continents and has remained primitive and intact, which could be balanced by other more evolved crustal components to form a mature bulk continental crust. [ABSTRACT FROM AUTHOR]

On 8 January 2022, a Moment Magnitude (Mw) 6.7 earthquake occurred in Menyuan, China. The epicenter was located in the western segment of the Lenglongling fault of the Qilian-Haiyuan fault zone. In this area, the Mw 5.9 Menyuan earthquake on 26 August 1986 and the Mw 5.9 Menyuan earthquake on 21 January 2016 successively occurred. The seismogenic structures of the 1986 and 2016 earthquakes are on the Northern Lenglongling fault, which is a few kilometers away from the Lenglongling fault. After the 2022 Menyuan earthquake, we collected GF-7 and Sentinel-1 satellite images to measure the surface deformation of the earthquake sequence. Based on the elastic dislocation theory, the fault model and fault slip distribution of the 2016 and 2022 Mengyuan earthquakes were inverted using coseismic surface displacements. The results show that the 2016 event is a reverse event, with the maximum coseismic surface displacement on LOS reaching 8 cm. The strike, dip, and rake of the earthquake rupture were 139°, 41°, and 78°, with the maximum slip reaching 0.6 m at a depth of 8 km. The surface rupture of the 2022 Mw 6.7 earthquake ran in the WNW–ESE direction with a maximum displacement on LOS of 72 cm. The main seismogenic fault of the 2022 event was the western segment of the Lenglongling fault. The strike, dip, and rake of the rupture were 112°, 85°, and 3°, with the maximum slip reaching 4 m at a depth of 4 km. The Coulomb failure stress change shows that the earthquake sequence generated a considerable positive Coulomb failure stress of more than 2 bar. These observations suggest that the earthquake sequence around Menyuan is mainly governed by the activities of the Lenglongling fault around the northeastern Tibetan Plateau. In addition, their sequential occurrences could be related to earthquake-triggering mechanisms due to stress interaction on different deforming faults. Thus, the Lenglongling fault has received a great amount of attention regarding its potential earthquake hazards. [ABSTRACT FROM AUTHOR]

This paper collects and analyzes the 1954–2017 monthly average reanalysis data from the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), the 1954–2017 haze days observation data from the National Meteorological Information Center/China Meteorological Administration (NMIC/CMA) and the PM2.5 daily average mass concentration data in 2013–2017 from the China Air Quality Online Monitoring Platform. The atmospheric apparent heat source Q1 (negative Q1 means cold source in winter) over the Tibetan Plateau in December of 1954–2017 is estimated based on thermodynamic equations, and the East Asian winter monsoon index (EAWMI) is calculated. In addition, the discrepancies of the air quality among China's five typical regions (Beijing–Tianjin–Hebei, Fen-Wei Plain, Yangtze River Delta, Pearl River Delta and Sichuan-Chongqing regions) under the joint influence of the Q1 and EAWMI are studied. Results show that when it is a strong cold source year, abnormal downdrafts and "temperature inversion covers" occur in areas far from the high terrain, resulting in increased pollution, while the opposite is true in weak cold source years. In strong EAWMI years, there is an abnormal northerly sinking cold flow in the lower layers of mid-high latitudes, which increases the pollution in the area south of 30° N, and the opposite is true in weak EAWMI years. Affected by the combined activities of the Q1 and the EAWMI, the meteorological conditions of the five typical regions are different, and thus present different air pollution characteristics. [ABSTRACT FROM AUTHOR]

Wildfire is an important ecological disturbance that can have cascading effects on ecosystem carbon (C) fluxes. Ecosystem respiration (ER) and soil respiration (SR) account for two of the largest terrestrial C fluxes to the atmosphere, and they play critical roles in regulating C–climate feedbacks. Here, the responses of ER, SR and their source components to experimental burning in a meadow grassland on the Tibetan Plateau were investigated. Fire treatment increased ER by 9% but decreased SR by 15%. The contrasting post‐fire responses of SR and ER can be explained by the behaviour of their source components; that is, fire increased aboveground plant respiration (Ragb) by 37%, but decreased heterotrophic respiration (HR) by 21%. Increases in ER and Ragb were mainly related to enhanced plant productivity, whereas smaller SR and HR were associated with reductions in microbial biomass and soil moisture. Accounting for the responses of ER, SR and their intrinsic components has advanced our understanding of how fire affects ecosystem C fluxes. Highlights: Fire treatment increased ecosystem respiration (ER) and aboveground plant respiration.Fire treatment decreased soil respiration (SR) and heterotrophic respiration (HR).Increases in ER and aboveground plant respiration were related to plant productivity.Reductions in SR and HR were caused by the suppressed microbial activity. [ABSTRACT FROM AUTHOR]

Climate change and human activity are changing the dynamics of the Qinghai-Tibet Plateau (QTP) environmental balance, which impacts the safety and stability of its infrastructure. The Qinghai-Tibet Railway (QTR) is the longest structure in the QTP, and some sections of the QTR’s embankment have been damaged due to freezing and thawing of permafrost. In this article, a modified SAR interferometry (InSAR) method for deformation monitoring is proposed and implemented. In this method, a seasonal deformation model based on the simplified Stefan equation has been adopted to measure the seasonal displacement. In particular, a linked coherence model is used to improve the effect of temporal correlation by defining a coherence parameter in the neighbouring pixel network. It was found that most of the study area had seasonal displacements of up to 20 mm. The deformation cross-section profile of the railway shows asymmetry between the two sides of the railway subgrade shoulders which may be related to sunny-shady slope effect. It was found that variable deformation along the QTR ranges from 0 to 30 mm, probably due to underlying permafrost conditions. Displacements of the experimental railway subgrade segment with varying types of cooling measurements are different, which shows their cooling efficiency variance. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Grenville-age terrane is identified in the Qilian orogen. • The Precambrian basement of the Qilian orogen is divided into four distinct mega-sequences. • ∼475 Ma metamorphism was related to the subduction of the Proto-Tethys Ocean. The Qilian orogen at the northeastern margin of the Tibetan Plateau records a complete history from continental breakup to oceanic basin evolution and back to continental collision during the Neoproterozoic to Paleozoic interval. The Qilian Ocean, as a branch of the Proto-Tethys Ocean, was connected to the Iapetus Ocean but is lesser known than its two more famous counterparts. This paper presents zircon U-Pb and biotite-muscovite 40Ar/39Ar isotope data from the Yemananshan Complex in the western Central Qilian belt to assess the age and provenance of late Mesoproterozoic-early Paleozoic successions in the Qilian orogen. The results indicate the Central Qilian belt is characterized by Late Mesoproterozoic-early Neoproterozoic orogenesis with magmatism from 1200 Ma to 900 Ma and clastic metasedimentary rocks deposited between 1050 and 920 Ma. Statistical analysis of detrital zircon data and auxiliary temporal information from the Qilian orogen affirms the notion that sedimentation occurred in four distinct megasequences: (1) 1950–1850 Ma, the oldest known strata, (2) 1250–920 Ma, during Grenvillian-Sveconorwegian orogenesis, (3) 840–760 Ma, the disintegration of Rodinia, and (4) 650–550 Ma, which is typical of the orogenic belts that sutured the Gondwana continental blocks. Metamorphic zircon and 40Ar/39Ar isotope data indicate early Paleozoic metamorphism at ca. 475 Ma, which overlaps with magmatic activity associated with arc-back-arc basin development in the Central Qilian belt, which was associated with subduction of the Proto-Tethys in eastern Gondwana. [ABSTRACT FROM AUTHOR]

• The early Neoproterozoic granitoids in the Qaidam block show typical S-type properties, generating via partial melting of Mesoproterozoic metasedimentary rocks. • These granitoids were formed under high-temperature and low-pressure conditions in a late syn- to post-collision setting. • Qaidam block was located at the core of the Rodinia supercontinent, adjacent to Laurentia, Baltica and Amazonia during the Neoproterozoic. Neoproterozoic granitoids are widely distributed in the Altyn Tagh, and provide indispensable information on the pre-Cenozoic tectonics and evolutionary history at the northeastern margin of Tibetan Plateau. In this study, zircon U-Pb geochronological results show that the granitoids were emplaced during the interval between 997 Ma and 901 Ma. Petrological studies reveal that these granitoids have high Al 2 O 3 and K 2 O, low CaO and Na 2 O contents with Al-rich minerals, such as muscovite, which show typical S-type properties. These Neoproterozoic granitoids contain abundant inherited cores of Mesoproterozoic age with ε Hf (t) values between 9.43 to 4.60. We interpret this to indicate magma generation via partial melting of Mesoproterozoic metasedimentary rocks. Based on a comparison to similar Neoproterozoic magmatic and metamorphic events described in the East Kunlun and North Qaidam, we suggest that the Altyn Tagh, East Kunlun and North Qaidam were part of the same terrane (Qadiam block) during the early Neoproterozoic. Petrogenetic data when combined with other geological and tectonic information suggest a late syn- to post-collisional setting rather than a syn -collisional setting. The Qaidam block was probably located adjacent to Laurentia, Baltica and Amazonia, during Neoproterozoic time. [ABSTRACT FROM AUTHOR]

Glacial stability on the Tibetan Plateau has declined sharply in the context of global warming. Previously, continental glaciers on the northwestern Tibetan Plateau were considered stable and had little susceptibility to ice collapse. However, in recent years, numerous continental glacier ice collapses have resulted in significant economic losses, casualties, and ecological environmental damage. This study focused on eight watersheds in the Ngari Prefecture of the northwest Tibetan Autonomous Region, specifically in the upper reaches of Zecuo Lake. Continental glacier ice-avalanche disaster factors were examined based on topography, climate, and geological structure. This study proposes a continental glacier ice-avalanche susceptibility assessment method that considers both internal and external factors by combining the analytic hierarchy process (AHP) and cloud theory. A comprehensive evaluation and analysis revealed that the eight watersheds in the upstream study area of Zecuo Lake were greatly affected by climate change and geological structure, and the susceptibility assessment ratings for all glaciers were high. Therefore, it is essential to strengthen the monitoring and early warning systems in areas of human activity. The findings of this study provide a scientific basis for predicting, preventing, and mitigating continental glacier avalanche disasters on the northwestern Tibetan Plateau. Additionally, the proposed method can be applied to areas with similar geological conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The far-field effects of the Indian-Asian collision and the crust-mantle processes triggered by the paleo-Pacific plate formed the Weihe Graben in the Paleogene. • The eastward extrusion of the Tibetan Plateau controls the evolution of the Weihe Graben since the Neogene. • The Weihe Graben was formed by a strike-slip and extensional combined mechanism in the Paleogene, but an extensional mechanism since the Neogene. The Weihe Graben is located in the composite area of the Tethys-Himalayan tectonic and circum-pacific tectonic domains and is an essential structural feature related to Cenozoic intracontinental deformation. However, two different hypotheses, sinistral strike-slip, and extensional mechanism, are proposed for the origin of this graben. In this study, we designed crust-scale analog models based on fault kinematics to better understand the deformation and dynamic mechanisms of the Weihe Graben. Fault kinematics shows early sinistral strike-slip and NW-SE extensional deformation and late NE-SW, S-N, and NW-SE extensional deformation. Our experimental results reveal that Model C1 (sinistral strike-slip + NW-SE extension) is the most similar to the geological structure of the Weihe Graben in the Paleogene. Furthermore, the NE-SW extension results in two larger subsidence areas in the northeast and southwest of the basin, similar to the formation of the two depressions during the Miocene. The S-N extension causes the basin to expand southward and northward, consistent with the sedimentary characteristics of Weihe Graben in the Pliocene. The NW-SE extension leads to relatively strong fault activity in the northwest and southeast of the basin, resembling the active fault characteristics since the Quaternary. Therefore, we propose that the Weihe Graben formed by a strike-slip and extensional combined mechanism in the Eocene-Oligocene, influenced by the far-field effects of the Indian-Asian collision and crust-mantle processes triggered by the stagnant paleo-Pacific plate. Subsequently, during the Neogene-Quaternary, the graben's development shifted towards an extensional regime under the influence of the eastward extrusion of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang Ocean played an important role in the formation of the Tibetan Plateau prior to the Cenozoic India–Eurasia collision. However, there are still uncertainties about the subduction polarity and timing of the Lhasa–Qiangtang collision. We conducted sandstone petrologic and detrital zircon U–Pb–Hf isotopic analyses on the Cretaceous Wada mélange, trench-fill strata and Duoni Formation in the Basu area in the eastern Bangong–Nujiang Suture Zone. The Wada mélange (∼114 Ma) exhibits block-within-matrix features and a detrital zircon U-Pb age spectrum characterized by multiple peaks at 114–180 Ma, 200–300 Ma, and 1800–2000 Ma. The trench-fill strata consist of coherent chert, sandstone, and mudstone, with a detrital zircon age spectrum dominated by a single peak at ∼120 Ma. The ε Hf (t) values of the 110–300 Ma detrital zircon grains in the Wada mélange and trench-fill strata range from −20 to +10 and are consistent with those of the South Qiangtang Terrane. The ε Hf (t) values of the ∼120 Ma detrital zircons are all negative, and these grains were likely derived from a remnant Cretaceous arc in the South Qiangtang Terrane to the north. These data suggest that the accretionary wedge was derived from the South Qiangtang Terrane during the northward subduction of the Bangong–Nujiang Ocean. The Duoni Formation (∼113 Ma) represents peripheral foreland basin deposits with the Lhasa Terrane as the basement. Provenance analysis indicates that these deposits received clastic material mainly from the South Qiangtang Terrane and to a lesser degree from the North Lhasa Terrane. Our results suggest that the Lhasa–Qiangtang collision occurred in the Early Cretaceous (∼113 Ma) in the eastern segment of the Bangong–Nujiang Suture Zone. • The Wada mélange and trench-fill strata (∼114 Ma) are associated with northward subduction. • The Duoni Formation (113 Ma) represents the peripheral foreland basin in the Basu area. • The eastern Bangong–Nujiang Ocean closed at ca. 113–114 Ma. [ABSTRACT FROM AUTHOR]