East Kunlun Research Articles

Large‐Scale Interseismic Strain Mapping of the NE Tibetan Plateau From Sentinel‐1 Interferometry

AbstractThe launches of the Sentinel‐1 synthetic aperture radar satellites in 2014 and 2016 started a new era of high‐resolution velocity and strain rate mapping for the continents. However, multiple challenges exist in tying independently processed velocity data sets to a common reference frame and producing high‐resolution strain rate fields. We analyze Sentinel‐1 data acquired between 2014 and 2019 over the northeast Tibetan Plateau, and develop new methods to derive east and vertical velocities with ∼100 m resolution and ∼1 mm/yr accuracy across an area of 440,000 km2. By implementing a new method of combining horizontal gradients of filtered east and interpolated north velocities, we derive the first ∼1 km resolution strain rate field for this tectonically active region. The strain rate fields show concentrated shear strain along the Haiyuan and East Kunlun Faults, and local contractional strain on fault junctions, within the Qilianshan thrusts, and around the Longyangxia Reservoir. The Laohushan‐Jingtai creeping section of the Haiyuan Fault is highlighted in our data set by extremely rapid strain rates. Strain across unknown portions of the Haiyuan Fault system, including shear on the eastern extension of the Dabanshan Fault and contraction at the western flank of the Quwushan, highlight unmapped tectonic structures. In addition to the uplift across most of the lowlands, the vertical velocities also contain climatic, hydrological or anthropogenic‐related deformation signals. We demonstrate the enhanced view of large‐scale active tectonic processes provided by high‐resolution velocities and strain rates derived from Sentinel‐1 data and highlight associated wide‐ranging research applications.

The role of crystal mush in porphyry systems: A case study from the Baishiya ore field, East Kunlun orogenic belt, northern Qinghai-Tibet plateau

Since a cold storage crystal mush reservoir has been gradually used to describe magmas in shallow crust, traditional mechanisms, such as wall-rock assimilation, melt-crystal separation, as well as magma mixing and mingling, must be used with caution because recycled antecrysts can play a significant role. As a result, magmatic processes accounted for texture, geochemistry, and mineralization diversity among ore-related porphyry, overlying (sub)volcanic rocks, and underlying pluton in porphyry systems remain ambiguous. The Baishiya igneous suite (East Kunlun orogenic belt, China) with porphyry-related skarn mineralization provides an opportunity to resolve this issue. Within the crystal mush concept, we propose a comprehensive model based on the subtle changes. First and foremost, large K-feldspar grains characterized by high Sr/Y ratios (52–134) in the top area of granodiorite have a slightly enriched lead isotopic signature, indicating a previously existed crystal mush equilibrated with K-feldspar. The locked crystal mush was injected by mantle-derived mafic melts, leading to a transfer in heat and volatiles from hot melts to cold crystal mush. The buoyant volatiles and loaded metals introduced by episodic mafic replenishments concentrated on the roof, providing a fluid-rich and thermal cycling condition for K-feldspar coarse graining. Some enlarged K-feldspar grains sunk into the bottom area due to gravity, and subsequently reacted with upwelling hot melts to form rapakivi textures. As a gradually waning of injection of mafic melts, crystallization drove fluid exsolution, forming magmatic-hydrothermal events. The finally solidified granodiorite acted as a host rock for a newly produced magma reservoir, but the following development was different. Catastrophic eruptions induced by tectonic stress transition led to a strong depletion of volatiles and associated metal endowment in the underlying magma reservoir, and subsequently left a barren magma source, terminating potential mineralization events. The residual felsic melts migrated upwards along previously formed magma conduits, and thus emplaced as barren porphyry dike. Our work reveals that recycling of K-feldspar antecryst induced by mafic injection contributes to high Sr/Y ratio in ore-related porphyritic granodiorite. Within a long-lived replenishment of mantle-derived magma, a crystal mush reservoir at shallow crustal levels can act as a ‘cooling pond’ to quench these hot melts, but accept volatiles and loaded ore-forming elements, concentrating metals by volatile buoyancy with the help of a compressional stress, which is presumably essential for late fluid exsolution from the reservoir’s roof.

Strain Field Features and Three-Dimensional Crustal Deformations Constrained by Dense GRACE and GPS Measurements in NE Tibet

The continuing impact between the Eurasia Plate and India results in the thickening and shortening of the N-S Tibetan Plateau. There has been strong tectonic movement along the boundary of the zones of deformation of the NE corner of the Tibetan plateau (NET) since the new tectonic period, with its dynamic mechanisms remaining controversial. Here, we use observations of 39 Continuous Global Positioning System (CGPS) gauges and 451 Crustal Movement Observation Network of China (CMONOC) campaign-mode stations to detect the three-dimensional deformation of the crust in the NET. Improved processing procedures are implemented to strengthen the patterns of strain throughout the NET. The principal component analysis (PCA) technique is introduced to decompose the time series into spatial eigenvectors and principal components (PCs), and the first three PCs are used to estimate and rectify common mode errors (CMEs). In addition, GRACE observations are used to detect deformation changes that account for non-tidal oceanic mass loading, hydrological loading, and surface pressure. The rectified deformation of the crust indicates the anisotropic nature of both the subsidence and uplift, and that the highest uplift rate of the Longmen Shan fault uplift reaches 7.13 ± 0.53 mm/yr. Finally, the horizontal velocity is further used to enumerate the strain rates throughout the NET. The results show that the shear band retained property in line with the strike-slip fault along the Altyn Tagh fault, the Qilian Shan faults, the Haiyuan fault, the West Qinling fault, the East Kunlun fault, and the Longmen Shan fault. In addition, the results further indicate that the whole NET shows a strong relationship with the mean principal rates of horizontal shortening strain. Extension and compression of the crust reasonably describe its sinking and uplifting.

Mid-Neoproterozoic magmatism in the South Qilian Belt, NE Tibetan Plateau and its tectonic implications

AbstractWidely distributed Mid-Neoproterozoic mafic rocks of the Qilian – Qaidam – East Kunlun region record the tectonic evolution of the northeastern Tibetan Plateau. This study presents whole-rock geochemistry, zircon U–Pb geochronology and Hf isotopes for the Xialanuoer gabbros of the central South Qilian Belt (SQB). Zircon laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating indicates that the gabbros were emplaced at ca. 738 Ma, indicating they are contemporaneous with mafic magmatism elsewhere in the northeastern Tibetan Plateau. The gabbros have low SiO2, Cr and Ni contents and Mg# values, are relatively enriched in light rare-earth elements (LREEs) and depleted in high-field-strength elements (HFSEs; e.g. Nb and Ta), have no positive Zr or Hf anomalies and have relatively high Nb/Ta but low Nb/La ratios. These data indicate that the Xialanuoer gabbros formed from calc-alkaline basaltic magmas that were originally generated by the partial melting of an enriched mantle of type-I (EMI-type) enriched region of the lithospheric mantle, underwent little to no crustal contamination prior to their emplacement, and have within-plate basalt geochemical affinities. Combining these data with the presence of widespread contemporaneous continental rift-related magmatism and sedimentation in the North Qilian, Central Qilian, South Qilian, Quanji, North Qaidam and East Kunlun regions suggests that the northeastern Tibetan Plateau underwent Mid-Neoproterozoic continental rifting, which also affected other Rodinian blocks (e.g. Tarim, South China, Australia, North America and Southern Africa).

Geochronology and geochemistry of Silurian pegmatites and related granodiorites from the Wudaogou area, southern East Kunlun Orogen, northern Qinghai–Tibetan Plateau

Geochronology and geochemistry of Silurian pegmatites and related granodiorites from the Wudaogou area, southern East Kunlun Orogen, northern Qinghai–Tibetan Plateau

Evolution of the Continental Crust in the Northern Tibetan Plateau: Constraints From Geochronology and Hf Isotopes of Detrital Zircons

To investigate the evolution of the continental crust in the northern Tibetan Plateau, detrital zircon U–Pb geochronology and Hf isotopes analysis were performed on two fluvial sand samples from North Qaidam (the Yuka and Shaliu rivers). A total of 443 detrital zircon U–Pb ages and 244 Hf isotopic results were obtained and reveal that the South Qilian, North Qaidam, and East Kunlun terranes show affinity to the western Yangtze Block. Age distributions of detrital zircons from the Yuka River cluster mainly in two age intervals of 1,000–700 and 480–400 Ma. The corresponding εHf(t) values are mostly negative, with depleted two-stage Hf model ages (TDM2) of 2.1–1.6 Ga. In contrast, age data for the Shaliu River fall in the ranges of 1,000–700, 460–380, and 260–200 Ma, with TDM2 ages of 2.0–1.6 and 1.6–1.2 Ga. In addition, zircons with Neoproterozoic ages from both river samples possess common Paleoproterozoic TDM2 ages (2.0–1.6 Ga, with a peak of 1.8–1.7 Ga), indicating that the South Qilian, North Qaidam and East Kunlun terranes were probably part of the same Neoproterozoic continent. The East Kunlun and North Qaidam terranes are inferred to include Mesoproterozoic continental crust (1.6–1.0 Ga), suggesting differences in crustal evolution between the East Kunlun–North Qaidam and Qilian terranes. Phanerozoic magmatism in these three terranes was sourced mainly from the recycling of ancient continental crust with minor contributions from the juvenile crust.

Highly differentiated felsic granites linked to Mo mineralization in the East Kunlun Orogenic Belt, NW China: Constrains from geochemistry, and Sr-Nd-Hf isotopes of the Duolongqiarou porphyry Mo deposit

The Mo deposits in the Kunlun-Qinling-Dabie orogen are mainly associated with porphyry or porphyry-skarn mineralisation in a collision or post-collision setting. However, collision-type Mo deposits that are related to granite and mineralization produced in magmatic systems remain poorly constrained. To better define the genetic relationship between the intrusions and Mo mineralization in collision setting, the geochronology, geochemistry, and Sr-Nd-Hf isotopes of the granodiorite and monzogranite in Duolongqiarou Mo deposit, East Kunlun Orogenic Belt (EKOB), NW China, are presented. Zircon U-Pb dating shows granodiorite and monzogranite ages of 237.6 ± 1.5 Ma and 236.8 ± 1.8 Ma, respectively, which is consistent with the molybdenite Re-Os weighted mean model age of 235.9 ± 1.4 Ma. This suggests that the granitic magma related to Mo mineralization at the Duolongqiarou formed during the Triassic (ca. 236 Ma). The ore-bearing monzogranites with high SiO2 contents (76.84–77.92 wt%) are peraluminous high-K calc-alkalic rocks, while the ore-barren granodiorites with low SiO2 contents (66.89–69.90 wt%) are metaluminous Na-rich calc-alkalic rocks. Both are enriched in large ion lithophile elements and light rare earth elements but depleted in high-field strength elements, which is characteristic of I-type granites. Ore-bearing and barren granites have similar εNd(t), εHf(t), and TDM2 age, indicating a similar magma source derived from partial melting of ancient Mesoproterozoic lower crustal components with involvement of mantle materials. The amphiboles of monzogranite show higher values of calculated pressures (average 122 MPa) and melt H2O content (average 5.7 wt%) than granodiorites, suggesting that monzogranites and granodiorites crystallized at different depths of the same magma chamber. Ore-bearing monzogranites show much lower contents of transition metals (e.g., Sc, V, and Cr), negative Eu anomalies (δEu = 0.32–0.46), and higher differentiation index values (94.52–96.92) compared to barren granodiorites. This suggests that high differentiation and fractionation promote Mo metal enrichment during magmatic evolution and subsequent formation of the magmatic-hydrothermal Duolongqiarou Mo deposit. The Duolongqiarou Mo deposit was formed in a collisional setting in response to the slab break-off of the EKOB Paleo-Tethys ocean. The results of this study combined with published data suggest that at least two generations of Mo polymetallic metallogenic events were observed in the Paleo-Tethys of the EKOB. This is very helpful to target porphyry Mo mineralization and guide regional exploration.

Genesis of the Xiarihamu Magmatic Ni-Co Sulfide Deposit in the East Kunlun Orogen, Northern Tibetan Plateau: In Situ Oxygen Isotope and Geochemical Perspectives

Abstract Convergent margins are commonly deemed to have poor potential to form giant magmatic Ni-Cu-(platinum group element) sulfide deposits, due to the possibly low lithospheric geothermal gradient and the small basaltic magma fluxes. This view, however, is challenged by the recent discovery of the Xiarihamu Ni-Co deposit in the East Kunlun orogen (northern Tibetan Plateau), which contains ~157 million metric tons (Mt) of sulfide ores at 0.65% Ni, 0.013% Co, and 0.14% Cu, making it the world’s 20th largest magmatic sulfide deposit. To investigate the mantle source nature, magmatic processes, and their genetic linkage to Ni-Co mineralization in orogenic belts, we presented new in situ orthopyroxene oxygen isotope and pyroxene trace element data from the mafic-ultramafic cumulate rocks at Xiarihamu. Our results show that orthopyroxene crystals have much higher δ18O (6.40–8.58‰) than those in unmodified mantle peridotite (5.72 ± 0.14‰). Orthopyroxene grains in the primitive harzburgite cumulates have the lowest δ18O values (6.40–7.71‰) and the highest Mg# contents (88.7–83.9). From the harzburgite to the evolved lithologies (e.g., websterite and gabbronorite), the δ18O values of orthopyroxene increase, whereas the Mg# values, Ni contents, and heavy/light rare earth element (HREE/LREE) ratios of orthopyroxene decrease, implying crustal contamination during magma fractionation. The δ18O variations and sharp increases in V/Sc and LREE/HREE ratios from the primitive orthopyroxene crystals (with the highest Ni and Mg#) to the evolved ones (with low Ni and Mg#) indicate that crustal contamination played a critical role in sulfide saturation. The absences of any trend in orthopyroxene δ18O values versus Mg# contents, Ni concentrations, and La/Yb ratios toward unmodified mantle values suggest an enriched mantle source. On the mid-ocean ridge basalt (pyroxene)-normalized multielement plots, both orthopyroxene, clinopyroxene, and calculated parental magma show LREE and large ion lithophile element (LILE) enrichments and depletions in Nb-(Ta), Sr, and Zr-(Hf). The predicted primitive magma trace element compositions and the high-δ18O characteristics of the high-Mg# orthopyroxene grains suggest that the Xiarihamu primitive magma was partly originated from the pyroxenite mantle metasomatized by subducted slab-derived melts and fluids. Given the lower solidus temperature of clinopyroxene relative to olivine, pyroxenites in the mantle wedge may generate voluminous high-Ni magmas during partial melting. The high-Ni magmas are likely conducive to magmatic Ni-Cu sulfide mineralization in orogenic belts.

Neoproterozoic and early Paleozoic metamorphism recorded in gneisses from the East Kunlun Orogenic belt

The East Kunlun Orogen (EKO) is a long-lived accretionary orogenic belt that records the Paleozoic–Mesozoic amalgamation processes of the East Asia continent. The belt consists mainly of various kinds of gneisses with minor amounts of eclogite and garnet amphibolite occurring as lenses. We report zircon U–Pb ages and Hf–O isotopic compositions for the granitic gneisses and paragneisses in the Xiarihamu area near Golmud in Qinghai Province, to investigate the metamorphic history and evolution of the orogenic belt. For the granitic gneisses, zircon U–Pb chronology reveals a Neoproterozoic magmatic event and an early Paleozoic metamorphic event. The magmatic crystallization ages of the two granitic gneisses are 920 ± 6 and 929 ± 2 Ma, and yield εHf(t) values of −8.4 to 1.7 and δ18O values of 7.94–11.19‰, suggesting their derivation mainly from continental crustal materials. The detrital zircons from the paragneisses record a Neoproterozoic metamorphic event and a Paleozoic metamorphic event. Most of the detrital zircons from the two paragneiss samples yielded ages of 2.1–0.9 Ga, indicating that the sources of the sediment were formed mainly during the Neoproterozoic to Paleoproterozoic. These Neoproterozoic magmatic and metamorphic events suggest that the EKO underwent a Neoproterozoic tectonothermal event that was related to the assembly of the Rodinia supercontinent. The similar tectonic histories of the EKO and North Qaidam belt (NQB) indicate they were probably part of a single tectonic unit during the Neoproterozoic. Some of the zircons have metamorphic overgrowth rims yielding two stages of Paleozoic metamorphic ages of ca. 440 Ma (438 ± 2 Ma) and ca. 420 Ma (419 ± 6 Ma, 416 ± 6 Ma, and 423 ± 6 Ma). Combined the discover of high-pressure mineral inclusions (jadeite + quartz) in these rims with the results in previous studies, the ages of these rims (ca. 440 Ma and ca. 420 Ma) are suggested to represent of HP-UHP metamorphism of the EKO. These age data imply that the gneisses in this study might share common early Paleozoic metamorphic event with the HP–UHP eclogites in the EKO.

Strain Distribution Along the Qilian Fold-and-Thrust Belt Determined From GPS Velocity Decomposition and Cluster Analysis: Implications for Regional Tectonics and Deformation Kinematics

The Qilian fold-and-thrust belt (QFTB) offers an excellent example to demonstrate the strain transition from strike–slip shearing to oblique crustal shortening, which plays an important role in dissecting the stress propagation of Indian–Eurasian convergence from the plateau interior to the surrounding blocks. Various geological or numerical models have attempted to describe the regional tectonic characteristics of the QFTB. However, these models only interpret one or part of the deformation behaviors in the QFTB, and the strain distribution across and along the QFTB as well as its deformation kinematics remains to be determined. Therefore, in this work, we applied the method of velocity decomposition and cluster analysis using combined GPS data to determine the strain partition or accommodation in different parts of the QFTB as well as tectonic relationships with surrounding blocks, which will contribute to distinguishing which model is more suitable for delineating the present-day deformation kinematics of the QFTB. Our analysis indicates that the western part of the QFTB is dominated mainly by crustal shortening perpendicular to the trend of the QFTB, coupled with lateral extension along the trend of the QFTB, while the eastern part of the QFTB is characterized mainly by lateral extrusion owing to the impact of two large eastward-striking left-slip faults (East Kunlun fault and Haiyuan fault), which are accommodated by an obvious velocity gradient boundary belt centered on two diamond basins (Qinghaihu and Gonghe basins) associated with their boundary faults. The active tectonics of the QFTB are obviously divided into two distinct groups: one group is a pure shear–strain pattern, accounting for strong crustal shortening in the western part of the QFTB, and the other group is a simple shear–strain pattern, accounting for the obvious lateral extrusion in the eastern part of the QFTB.

Post-UHP tectonic evolution of the East Kunlun orogenic belt, northern tibetan plateau: insight from the regional-scale crustal anatexis

ABSTRACT Extensive crustal anatexis is common during the decompressional exhumation of deeply subducted continental crust and the delamination of a collision‐thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun orogenic belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composition of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecontemporaneous A- and I-type granites with high magmatic zircon εHf(t) values and S-type granites with low magmatic zircon εHf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision‐thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting.

The chronological and geochemical characteristics of Triassic gabbro diorite in the Hongshuihe area of the East Kunlun Orogenic Belt, Northwest China

The chronological and geochemical characteristics of Triassic gabbro diorite in the Hongshuihe area of the East Kunlun Orogenic Belt, Northwest China

Generation of crystal-rich rhyodacites by fluid-induced crystal-mush rejuvenation: Perspective from the Late Triassic Nageng (sub-)volcanic complex of the East Kunlun Orogen, NW China

Remobilization of upper crustal crystal-rich magma reservoirs (“crystal mush”) following melt extraction has been widely invoked in the formation of crystal-rich erupted products. However, the melt storage duration and conditions, and the pre-eruptive magma chamber processes remain poorly understood. Here, we present new whole-rock elemental and Sr-Nd-Pb isotope data, and zircon U-Pb-Hf isotope and trace element data of the Nageng (sub-)volcanic complex in the East Kunlun Orogen of NW China. This complex consists of the highly-evolved (high SiO2, Rb/Sr) crystal-poor rhyolite and less-evolved crystal-rich rhyodacite and dacite porphyry. These rock types are genetically linked, based on their similar chondrite-normalized REE patterns and NdHf isotopes, and their linear correlation trends of 208Pb/204Pb and 207Pb/204Pb vs. 206Pb/204Pb. Their depleted whole-rock εNd(t) (−9.74 to −7.37) and zircon εHf(t) (−7.16 to −3.48) values, together with their Proterozoic two-stage Hf model ages (1707–1474 Ma), are indicative of an ancient lower crustal magma source. The overlapping zircon ages but distinct composition (74–80 vs. 60–66 wt% SiO2) and crystallinity (~5 vs. 30–40 vol%) between the crystal-poor rhyolite and dacite porphyry can be explained by melt extraction from the crystal mush zone. The lack of resorption texture and large age interval (~8 Myr) between the zircon core (ca. 228 Ma) and rim (ca. 220 Ma) indicate that the crystal mush remained partially molten for protracted duration. The melt storage condition was constrained by Ti-in-zircon thermometry to be low-temperature, around the granitic solidus (650–700 °C). The crystal-rich nature and slightly negative Eu anomalies suggest that the dacite porphyry was formed in the roof zone (solidification front) of the crystal mush. The occurrence of resorbed zircon core (ca. 220 Ma) overgrown by much younger rim (ca. 213 Ma) for the crystal-rich rhyodacite demonstrates long-term rejuvenation of a semi-solidified crystal mush. The similar zircon core-rim Ti contents and Th/U, Yb/Gd, Zr/Hf ratios preclude that the crystal mush was rejuvenated by hotter, more mafic magmas. However, the widespread fluorite-rich magmatic-hydrothermal veining, combined with the reduced nature (indicated by the zircon Ce4+/Ce3+ drop from core to rim) of the crystal-rich rhyodacite, imply that the volatile-rich fluid influx may have been important in reactivating the crystal-mush for later crystal-rich rhyodacite eruption.

Petrogenesis and Geodynamic Implications of Late Triassic Mogetong Adakitic Pluton in East Kunlun Orogen, Northern Tibet: Constraints from Zircon U–Pb–Hf Isotopes and Whole-Rock Geochemistry

Adakites or adakitic rocks usually show special geochemical signatures and are petrological probes to reveal the tectono–magmatic evolutionary history of paleo–orogenic belts. Here, we present a comprehensive study on the zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopes of Mogetong adakitic pluton in East Kunlun orogen, Northern Tibetan Plateau, to constrain its petrogenesis and tectonic setting, and thus to reveal its implications for the Paleo–Tethyan orogeny. The studied pluton comprises of quartz monzonite porphyry with zircon U–Pb crystallization age of ca. 215 Ma, which is coeval to their diorite enclaves (ca. 212 Ma). The quartz monzonite porphyries have intermediate SiO2 (63.31–65.74 wt%), relatively high Al2O3 (15.52–16.02 wt%), K2O (2.83–3.34 wt%), and Sr (462–729 ppm), but low Y (9.14–15.7 ppm) and Yb (0.73–1.39 ppm) with high Mg# (47–55), Sr/Y (30–57) and La/Yb ratios resembling typical high–K calc-alkaline and high Mg# adakitic rocks. Zircon Lu–Hf isotopes show that the studied samples have weakly juvenile zircon Lu-Hf isotopes (εHf(t) = 1.80–4.03) with older model age (1.00–1.14 Ga). The relative low content of Cr (14–59 ppm) and Ni (8–30 ppm), as well as the petrological, geochemical, and Lu-Hf isotopic data, indicates that the Mogetong adakitic rocks were generated by partial melting of thickened lower crust with a certain contribution of the underplated mantle-derived magma in slab break-off setting. This study shows that the Late Triassic adakitic magmatism in East Kunlun orogen may be the response of tectonic transition from oceanic subduction to post–subduction extension, and the reworking of ancient continental crust with subsequent variable crust-mantle magma mixing is the major mechanism of continental crust evolution in the Paleo–Tethyan orogenic belt.

Influence of Topographic Shading on the Mass Balance of the High Mountain Asia Glaciers

Most studies attribute the glacier mass balance within High Mountain Asia (HMA) to climate change, ignoring the influence of its complex terrain. Knowledge of the influence of this complex terrain is crucial for understanding the spatial variability in its mass balance. However, there is a lack of any systematic assessment of this influence across HMA. Therefore, in this study, we used the glacier outlines and raster data (SRTM DEM, slope and aspect) to calculate the topographic shading of all 97,965 glaciers within HMA during the ablation period, which is regarded as a major index of the influence of complex terrain on the mass balance. The results showed that 27.19% of HMA glacier area was subjected to topographic shading, and regional differences were significant with respect to both their altitudinal and spatial distributions. The topographic shading contributed to the protection of the smallest glaciers from solar illumination. Furthermore, we found a significant correlation between the topographic shading and mass balance in these small north-facing glaciers. However, these small glaciers were most prevalent in the north-facing orientation, especially in West Kunlun, East Kunlun, Inner Tibet Plateau and Qilian Shan, where shading was found to increase with decreases in the glacier area. This indicates that complex terrain can affect the spatial distribution of the mass balance by altering the solar illumination pattern.

Interaction between historical earthquakes and the 2021 Mw7.4 Maduo event and their impacts on the seismic gap areas along the East Kunlun fault

On May 21, 2021 (UTC time), an Mw7.4 earthquake struck Maduo County, Qinghai Province, China. The rupture of this typical strike-slip event and its aftershocks along the Kunlun-Jiangcuo fault (JCF) propagated approximately 170 km from the epicenter. In this study, we calculated the coseismic and postseismic Coulomb stress changes induced by 14 historical earthquakes and investigated their impacts on the 2021 Maduo source area. We found that the JCF is in the stress shadow of these historical events with a combined ΔCFS range of approximately − 400 to − 200 kPa. Since the seismogenic fault of the 1937 event is nearly parallel and close to the JCF, the rupture of the 1937 event had the greatest inhibitory effect on Maduo source area. We hypothesize that the actual loading rate at the depth of the seismogenic layer in the Maduo source area is much higher than the simulated value (0.3 kPa/a). Consequently, the Maduo earthquake still occurred despite the considerable delaying effect of these historical earthquakes (especially the 1937 event). Our findings also indicate that the tectonic stress in the eastern Bayanhar block is still rapidly accumulating and adjusting. Our investigation further reveals the enhanced stress induced by the historical and Maduo events with ΔCFS values of approximately 30–300 kPa and 50–300 kPa on the Xidatan-Dongdatan segment (XDS) and the eastern end of the East Kunlun Fault (EKF), respectively, not only on the Maqin-Maqu segment (MMS) but also at the eastern end of each branch segment of the EKF. Hence, considering the accumulation of tectonic stress, we suggest that the seismic hazard in these two regions has been promoted.Graphic

Early palaeozoic arc-continent collision in East Kunlun, northern Tibet: evidence from the minerology, geochemistry, and geochronology of the Adatan garnet amphibolites

ABSTRACT The evolution of the Tethys is one of the key issues in revealing the global ocean-continent transition tectonic process. The East Kunlun Orogenic Belt (E-KOB) in the northern Tibetan Plateau witnessed the subduction-accretion process of the Proto- and Palaeo-Tethyan Oceans formed a trench-arc-back arc basin system. Thus, this back arc basin is a window for exploring the tectonic evolution of the Tethys. In this study, the Adatan garnet amphibolites and the host paragneiss were investigated and used to constrain the evolution of the back arc basin. The mineralogical observations and microstructure of the garnet amphibolite suggest the successive formation of three mineral assemblages: a Hb + Pl + Ilm inclusion assemblage within garnet cores, a Grt + Pl + Hb + Bit + Phe matrix assemblage, and a retrograde assemblage of white-eye coronas around the garnet. The thermobarometric calculations suggest a clockwise P-T path with peak metamorphic conditions of 10.1–12.6 kbar and 715–830°C and a subsequent near-isothermal decompression process. The geochemistry indicates that the protolith of the garnet amphibolites was formed in a subduction-related tectonic setting with enriched mid-ocean ridge basalt (E-MORB) geochemical characteristics. U-Pb zircon dating reveals that the crystallization age of the garnet amphibolite’s protolith is ca. 457–452 Ma. Based on field occurrences, the protolith of the amphibolite was probably mafic dikes that intruded into the paragneiss due to subduction of the back-arc basin. Both the garnet amphibolite and gneissic rocks experienced contemporaneous metamorphism at ca. 420–410 Ma, suggesting that a crustal thickening event occurred due to closure of the back-arc basin and arc-continent collision. Based on the above evidence and the results of previous studies, it can be concluded that the Qimantagh back arc basin involved opening, subduction, and closure tectonic processes at ca. 486 Ma, ca. 460 Ma and ca. 420–410 Ma, respectively.

Geology, geochronology and geochemistry of the Saishitang Cu deposit in the East Kunlun Orogenic Belt,NWChina

The Saishitang deposit, located in the eastern part of the Eastern Kunlun Orogenic Belt, NW China, hosts important Cu mineralization. The ore occurs as stratiform bodies in Lower–Middle Triassic siltstone and siliceous rock and as lenticular bodies at the contacts between quartz diorite and marble. The whole‐rock geochemistry and Si–O isotopic compositions of the siliceous rocks suggest a sedimentary origin. The quartz diorite has a weighted mean zircon U–Pb age of 215.5 ± 0.9 Ma. The quartz diorite exhibits high SiO2(63.91–69.48 wt%), Al2O3(14.98–17.11 wt%) and Na2O (2.17–4.58 wt%) contents, with A/CNK values of 0.79–1.10, similar to those of calc‐alkaline I‐type granites. The quartz diorite exhibits weak negative Eu anomalies (δEu = 0.80–0.99), enrichment in light rare earth elements, Rb, Ba, K and Pb and depletion in heavy rare earth elements, Nb, Ta, P and Ti. The Pb isotopic compositions suggest that the skarn ore, quartz diorite and host rocks are closely correlated, reflecting a common source. By contrast, the Pb isotopic compositions of sulphide ores hosted within siltstone are heterogeneous, suggesting multiple lower‐crustal and upper‐mantle sources. By integrating our geological and geochemical data, we propose that the Saishitang deposit was formed by exhalative sedimentary mineralization in a back‐arc basin and overprinted by Indosinian skarn mineralization in a post‐collision extensional environment.

Tectonic uplift along the northeastern margin of the Qinghai–Tibetan Plateau: Constraints from the lithofacies sequence and deposition rate of the Qaidam Basin

The uplift processes of the Qinghai–Tibetan Plateau is of great significance for understanding the tectonic dynamics and monsoons in East Asia. In this study, the spatiotemporal characteristics of the tectonic uplift along the northeastern margin of the Qinghai–Tibetan Plateau are discussed from a basin–orogen coupling perspective on the basis of detailed analyses of stratigraphy and sedimentology of the Qaidam Basin and comparisons with those of the Xining, Lanzhou, Linxia, Guide–Xunhua, and Jiuquan basins. The asynchronous tectonosedimentary events characterized by alluvial conglomerates at the Early Jurassic–Cretaceous, ~53 Ma, ~40 Ma, ~22 Ma, ~15 Ma, and <2.5 Ma have been preserved in wells at different locations. Consistently, the deposition rates indicate three episodes of accelerated deposition at ~40 Ma, ~20 Ma, and ≤5 Ma in the Cenozoic. Therefore, we believe that the orogenic uplift along the northeastern margin of the Qinghai–Tibetan Plateau can be divided into four stages: Jurassic–Cretaceous, ~40–20 Ma, ~20–5 Ma, and <5 Ma. During the Jurassic–Cretaceous, tectonic activation and uplift occurred in the ancient Qilian orogenic belt, which formed in the Early Paleozoic. By ~40 Ma, the deformation due to the growth of the “proto-Tibetan Plateau” had propagated to the Qiman Tagh Shan–East Kunlun Shan–Ela Shan–West Qinling Mountain chain. Controlled by the tectonic thrusting of the eastern Kunlun Mountains, the Qaidam Basin entered a stage of comprehensive development. At ~20 Ma, the deformation front of the Qinghai–Tibetan Plateau reached the Qilian Shan. The unified Paleogene compressional basin in the northern West Qinling Mountains split into secondary basins, such as the Xining, Lanzhou, Linxia, Guide–Xunhua, and Gonghe basins, which evolved independently. At ~5 Ma, the entire Qinghai–Tibetan Plateau entered a rapid uplift stage, and the large lacustrine basins in and around the plateau shrank and disappeared.

Research on deformation characteristics of the 2021 Qinghai Maduo MS7.4 earthquake through coseismic dislocation inversion

Over the past 70 years, the Qinghai Maduo Ms7.4 earthquake (May 22, 2021) has been the only earthquake with a magnitude of ≥7 that has occurred within the Bayan Har Block. To investigate the deformation process of this earthquake, we acquired the Interferometric Synthetic Aperture Radar (InSAR) coseismic deformation field based on Sentinel-1 SAR images, which showed that the maximum line of sight (LOS) displacement was ~1 m. By combining this information with the results of our field investigation, the fault slip distributions were obtained by inversion using the single- and double-fault models, wherein the latter model showed better inversion results than that of the former. According to the inversion results, the overall rupture pattern was predominantly left-lateral strike-slip, with a released seismic moment of ~Mw7.5. Specifically, the principal seismogenic fault had a strike of 283°, dip of 91°, and maximum slip of 4.87 m; the branch fault along the eastern segment of the rupture had a strike of 110°, dip of 94°, and maximum slip of 2 m. Conversely, the results derived from the Global Navigation Satellite System (GNSS) strain rate field before the earthquake indicated that the Maduo earthquake occurred in East Kunlun,which is characterized by the largest maximum shear strain rate. The strain accumulation rate (~2.5 × 10−8/yr) was significantly lower than that of the Xianshuihe fault zone on the southern boundary of the Bayan Har block and the East Kunlun fault zone on its northern boundary. Furthermore, pre-seismic deformation near the seismogenic fault was relatively gentle, showing partial late seismogenic characteristics.