Southern Pamir Research Articles

The N-S direction strike-slip activities in the Pamir hinterland under oblique convergence: the 2015 and 2023 earthquakes

SUMMARY The prominent Pamir plateau holds considerable significance in comprehending the processes of Asian continental collisional orogeny. However, due to harsh natural conditions and low seismic activity within the Pamir hinterland, our understanding of this region remains deficient. Recent major events and the accumulation of geodetic observations present a rare opportunity for us to get insights into the tectonic activities and orogenic processes occurring in this region. First, employing Sentinel-1 and Advanced Land Observation Satellite (ALOS)-2 Synthetic Aperture Radar (SAR) images, we acquire coseismic displacements associated with the most recent earthquakes in 2015 and 2023. Subsequently, we conduct the source models inversion with the constraints of surface displacements based on a finite-fault model. Our results reveal displacements ranging from −0.8 to 0.8 m for the 2015 Mw 7.2 Tajik earthquake and −0.25 to 0.25 m for the 2023 Mw 6.9 Murghob event, respectively. The optimal three-segment model for the 2015 event ruptured a fault length of 89 km with a surface rupture extending 59 km along the Sarez–Karakul fault (SKF), characterized predominantly by left-lateral strike-slip motion, with a maximum slip of 3.5 m. Meanwhile, our preferred uniform slip model suggests that the 2023 event ruptured an unmapped fault in the southern Pamir region with a strike angle of 31° and a dip angle of 76.8°. The distributed slip model indicates that the 2023 event ruptured a fault length of 32 km, resulting in an 8 km surface rupture. This event is characterized by left-lateral strike slip, with a peak slip of 2.2 m. Secondly, the Coulomb stress calculations demonstrate that the 2023 event was impeded by the 2015 event. Finally, interseismic Global Positioning System data revel a relative motion of 3.4–5.7 mm yr−1 in the N-S component and 3.2–3.8 mm yr−1 in the E-W component along the SKF in the Pamir hinterland, respectively. These N-S direction strike-slip activities and slip behaviours support an ongoing strong shear and extension in the Pamir regime, which is a response to the oblique convergence between the Indian and Eurasian plates.

Tectonic evolution of the South Pamir Orogen: Insights from the Permian to cretaceous magmatism

The Pamir orogen originated through the amalgamation of various arc terranes. Despite undergoing numerous studies, the subduction polarity and time regarding the accretion processes remain inadequately constrained. To address these issues, we carried out a detailed study of zircon and apatite U-Pb ages, zircon Hf isotopes, and whole-rock geochemistry for the Permian to Cretaceous gabbro, volcanic rocks and granitoids from the Southern Pamir and the Rushan-Pshart suture. Three stages of magmatism are identified, including 279–266 Ma gabbro and andesite to dacite, 209–208 Ma granitoids, and 108–103 Ma gabbro and granitoids, respectively. The Permian gabbro and basaltic andesite to dacite in Pshart Range are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), but are depleted in Ta, Nb, and Ti, suggesting formation from an enriched mantle source in a subduction zone. The Late Triassic I-type granitoids are typical arc calc-alkaline magmatic rocks with εHf(t) values varying from −8.7 to −3.5, which mainly sourced from the partial melting of mixed crustal sources predominately consisting mafic rocks with minor metasedimentary rocks. The Early Cretaceous Pshart granites are I-type granites with relatively low εHf(t) values ranging from −14.6 to −2.9, suggesting that they were crust-derived rocks. The Early Cretaceous Bazardara granites are identified as A2-type granites with the εHf(t) values ranging from −18.3 to +5.3, and were derived from mixing of mantle-derived and crust-derived magmas, or interaction between mantle melts and old crustal rocks. The early Cretaceous gabbro exhibits -MORB-like geochemical characteristics with flat REE pattern (La/YbN = 4.96), moderate enrichment of LILEs and weak depletion of Nb, Ta and Ti (Nb/LaPM = 0.94). Thus, the early Cretaceous A2-type granite, E-MORB-like gabbro and volcanic rocks were formed in an extensional setting. Our new data indicate that the southward subduction of the Rushan-Pshart oceanic slab started in the Early Permian and continued to the Late Triassic. Moreover, combining the previous data, we conclude that the Early Cretaceous granites and gabbro in the Southern Pamir formed in an extensional environment due to the southward rollback after northward near-flat subduction of the Neo-Tethyan oceanic lithosphere.

Carboniferous bimodal volcanic sequences along the Northeastern Pamir: Evidence for back-arc extension due to northward subduction of the Paleo-Tethys

The Pamir plateau lies at the western end of the Tethys domain recording the entire evolution from the opening of the Proto-Tethys to the final closure of the Neo-Tethys. During this long-term evolution, the details of the initial subduction of the Paleo-Tethys and the final amalgamation of the main terranes in the Pamir are still controversial. The Carboniferous bimodal volcanic sequences along the Northern Pamir may supply the key evidence to reveal the subduction process of the Paleo-Tethys Ocean. This study presents the detailed stratigraphic architecture, petrography, geochronological and geochemical data of the Carboniferous−Permian volcanic rocks along the Northern Pamir in western China bordering Tajikistan. Zircons from two plagioclase phenocryst-rich basalts, and an andesite, volcanic agglomerate, and granitic sill emplaced in the basalts yield concordant ages of 319.5 ± 2 Ma, 322.7 ± 1.6 Ma, 288.7 ± 2.5 Ma, 301.6 ± 4.2 Ma, and 300.4 ± 1.5 Ma, respectively. The basalts show mid-oceanic-ridge basalt−like geochemical features with flat to depleted light rare earth element trends [(La/Yb)N = 0.68−1.82], depleted whole-rock εNd(t) (6.44−7.85), and zircon εHf(t) (6.3−10.1) values, suggesting they are primitive magmas derived from a depleted mantle source metasomatized by earlier subduction in line with their low Nb/La ratios (0.30−0.64). As for the intermediate-acid volcanic rocks (andesite and dacite), they show enrichment of large ionic lithophile elements (e.g., Rb, Ba, and Sr) and depletion of high field strength elements (e.g., Nb, Ta, and Ti) as well as negative εNd(t) values ranging from −0.97 to −0.75, demonstrating that they are primitive magmas derived from partial melting of the metasomatized lithospheric mantle source, followed by crystal fraction of hornblende, plagioclase, and minor quartz. Taking together the stratigraphic features, rock associations, and geochemical signatures, the Carboniferous basalts share most features with the Okinawa and the Mariana back-arc basalts. Integrating the new data with the previous studies, we construct a detailed evolution process of the Paleo-Tethys Ocean at the Pamir, i.e., extension of the filled residual Proto-Tethys Ocean between the Tarim and the Northern Pamir induced by the northward Paleo-Tethys subduction in the early Carboniferous, gradually waning of the back-arc basin from the late Carboniferous to the Early Permian, and finally, the closure of the Paleo-Tethys Ocean led to the amalgamation of the Northern, the Central, and the Southern Pamir, resulting in the initial architecture of the Pamir.

Moisture sources for precipitation over the Pamirs Plateau in winter and spring

AbstractThe abundant precipitation over Pamirs Plateau (PP) in spring and winter plays a vital role in the water resources over the arid areas of Central Asia. Understanding the moisture sources and water vapour transportation associated with precipitation are very important, but there were few studies investigating the moisture sources of PP. We used a Lagrangian model driven with the Weather Research and Forecasting output to analyse the moisture sources at Northern Pamirs Plateau (NPP) and Southern Pamirs Plateau (SPP) in spring 2016, 2009 and 2001, and in winter 2016, 2010 and 2017, as the seasonal precipitation in PP was the largest, median and lowest during 2001 to 2018, and the precipitation in spring and winter was much higher than that in summer and autumn. The moisture sources from four regions were quantified: Atlantic‐Europe‐Africa, Arctic‐Northern Asia, Indian Ocean, and moisture recycling from the PP. Atlantic‐Europe‐Africa and Indian Ocean are the dominant moisture source regions in spring and winter, which contribute more than 70% to the total moisture affecting the precipitation at PP. The contributions of Indian Ocean are higher at SPP than those at NPP in spring and winter. The contributions from Arctic‐Northern Asia and PP are generally low, except that the moisture from PP region contributed 19% to the spring precipitation at NPP, indicating the importance of a local moisture source in enhancing the spring precipitation at NPP. The moisture contributions originating from the different source regions show great differences between winter and spring. The moisture transportation is affected by westerlies, and the zonal winds in spring affect the moisture transportation, while the meridional winds over the Arabian Peninsula mainly affect the moisture transportation in winter.

Early Cretaceous displacement on the Tanymas thrust fault, Northern Pamir, Tajikistan, and regional tectonic implications

An ongoing question in understanding the evolution of the Himalayan-Tibetan orogeny is how much of the observed upper crustal shortening and crustal thickness is related to the Cenozoic collision between India and Asia vs earlier tectonic events along the southern margin of Asia. While the Pamir Mountains located at the western end of the orogen have been proposed to have experienced significant Cenozoic shortening, recent studies have interpreted upper crustal shortening to be primarily mid- to Late Cretaceous. To further understand the timing of upper crustal deformation in the Pamir, we investigated synorogenic clastic deposits within the footwall of the north-dipping Tanymas thrust fault along the suture between the Northern and Central Pamir terranes. Sandstones from these deposits were analyzed by detrital zircon U-Pb, zircon fission track, and muscovite 40Ar/39Ar analyses to assess the age and source of the detritus. Results show the deposits were sourced from the Northern Pamir (hanging wall of the Tanymas thrust) and provide an Early Cretaceous maximum deposition age of ∼130–120 Ma, interpreted to constrain their age and date motion on the Tanymas thrust fault as Early Cretaceous. Our results, integrated with previous studies, show Cretaceous deformation in the Pamir began in the Northern Pamir (∼140–110 Ma) before sweeping into the Southern Pamir in the mid- to Late Cretaceous (∼110–75 Ma). These results are consistent with previous interpretations of an Early Cretaceous phase of shallow- or flat-slab northward subduction followed by slab rollback and southward migration of deformation and magmatism in the mid- Cretaceous.

Post-collisional magmatism associated with the final closure of the Rushan-Pshart Meso-Tethys Ocean in Pamir, Tajikistan: Inference from Cretaceous igneous rocks of the Pshart accretionary complex

The Pamir orogen was formed by the subducted accretion and amalgamation of Cimmerian terranes from the northern margin of Gondwana with the southern margin of Eurasia. The Mesozoic magmatic rocks are widespread in Pamir and record the tectonic evolution in different stages. The Rushan–Pshart suture zone represents an ancient ocean between Central and Southern Pamir. This paper reports the petrography, geochronology, and geochemistry of Cretaceous granites and diabase dikes that intrude into the Pshart complex. The granites were emplaced between 124 and 118 Ma, based on their zircon U-Pb ages. These granites are characterized by high-K calc-alkaline, low magnesian, and high SiO2, A/CNK, and K2O+Na2O values. They also display strong depletion of Ba, Sr, Eu, and Ti and comparatively weak negative Nb anomalies in spidergrams. Thus, we proposed in this study that these are highly fractionated, strongly peraluminous S-type granites. They were generated by the partial melting of the metasedimentary rocks in the plagioclase stability field and underwent subsequent fractional crystallization during their ascent. The diabase dikes contain low SiO2, and high MgO levels and negative Nb and Ta anomalies, which were interpreted to form in an extensional environment. Late Jurassic–Early Cretaceous closure of the Rushan–Pshart Ocean and subsequent foundering of its oceanic lithosphere caused local extension and upwelling of the asthenospheric mantle. The underplating of mafic magma provided a heat source to melt the metasedimentary-derived granitic that formed in the initial post-collisional environment. The subsequent local extension caused the emplacement of diabase dikes. Based on our new data and combined with data from previous studies, we concluded that the Rushan–Pshart suture zone is the remnant of the Meso-Tethys Ocean and may represent the western continuation of the Bangong–Nujiang suture of the Tibetan Plateau.

Reconstruction of the Meso-Cenozoic tectono-geomorphological evolution of the Keguqin mountain in the Central Tian Shan based on geomorphological analysis and low-temperature thermochronology

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

A newly identified cryogenian (ca. 806 ma) basement tonalite gneiss from the Eastern Karakoram, NW India: Constraints from geochemistry and zircon U-Pb geochronology

The Karakoram Terrane (KT) represents the southern margin of the Eurasian Plate, mainly consisting of Late Jurassic-Early Cretaceous subduction-related granites and post-collisional Miocene leucogranites, which intrude the Late Neo-Proterozoic basement. We report for the first time the existence of the Cryogenian KT basement as recorded from the geochemistry and geochronology of tonalite gneiss (ca. 806 Ma) in the southeastern Karakoram terrane, NW India. Geochemically, the studied tonalite gneiss is slightly peraluminous (Molar Al2O3/CaO+Na2O+K2O=1.1), calc-alkaline volcanic-arc granitoid, strongly fractionated REE (LaN/YbN=33.99), and high Sr/Y =19.75, more akin to its affinity with Tonalite–trondhjemite–granodiorite (TTG)/adakite. The whole-rock elemental data suggest that tonalite gneiss is more likely sourced from ancient mafic lower crust where garnet remained in the residue. The petrogenetic modeling of REE suggests that the melt similar to the observed tonalite gneiss can be generated through ∼50% partial melting of a mafic lower crust with garnet, clinopyroxene, and amphibole assemblage. The synthesis and comparison of present and published Proterozoic magmatic records on the rocks from KT strongly dictate that the produced partial melt similar to observed tonalite gneiss most likely served as the parental melt for the development of TTGs in the Southern Pamir and more evolved granitoid in the Central Tibetan terrane. We propose that the studied tonalite gneiss from the southeast Karakoram is a product of Neoproterozoic Andean-type orogeny formed on the northwestern margin of the Rodinia supercontinent. Thus, our study favors the first time, the position of KT within the Cimmerian belt along with other East Asian continental blocks.

Mesozoic Tectonic Evolution in the Kurgovat‐Vanch Complex, NW Pamir

AbstractDifferent crustal deformation histories between Tibet and the Pamir reflect along‐strike variations in geodynamics of the Tethys orogen. To investigate the less well‐documented deformation history of the Pamir, which has been a barrier in understanding the nature of these differences, we conducted an integrated study in the Kurgovat‐Vanch region, NW Pamir. The lithologies are primarily Ediacaran‐to‐Carboniferous metasedimentary rocks intruded by Carboniferous plutons, which then experienced Late Triassic to Early Jurassic regional metamorphism. Structural mapping and analyses document a low‐angle NW‐directed thrust fault, the Poshkharv thrust, separating the overlying upper‐greenschist facies Poshkharv complex from the underlying amphibolite facies Kurgovat complex. Regional geologic maps indicate the Poshkharv thrust continues for ∼300 km across the NW Pamir. Our study also documents another regional thrust fault, the top‐to‐the‐SE Vanch thrust that juxtaposes the Southern Kurgovat complex above the lower‐grade Vanch complex in the south. Biotite 40Ar/39Ar thermochronology indicates Early Cretaceous movement on all structures with ∼135–125 Ma exhumation along the NW‐directed Poshkharv thrust and ∼125–115 Ma exhumation along the SE‐directed Vanch thrust. Regional crustal deformation in the Northern Pamir was formed in a Cretaceous retro‐arc setting, unrelated to the Cenozoic India‐Asia collision. Cretaceous deformation in the NW Pamir was broadly coeval with the NE Pamir, but preceded Cretaceous shortening and coeval arc magmatism in the Southern Pamir. We interpret Early Cretaceous thrusting and crustal thickening followed by southward migration of shortening and magmatic flare‐up in the Pamir to have resulted from a transition of Neotethys subduction from northward flat‐slab advancing to southward retreating.

Cretaceous basalt-andesite sequence in the Southern Pamir: arc—back-arc architecture at the Pamir Plateau genetically related to the northward flat subductions of the Neo-Tethys Ocean

The Pamir-Karakorum is one of the most important regions for our understanding the Tethys evolution. Although it is commonly known that the northward subduction of the Neo-Tethys Ocean induced the formation of the magmatic arc in Southern Pamir, the temporal-spatial configuration of the arc—back-arc during the Neo-Tethys evolution remains unclear. In this study, we report sedimentary feature, petrography, zircon U Pb ages and Hf O isotope compositions as well as bulk-rock and mineral geochemistry of the well-preserved Cretaceous volcanic sequence in Chinese Wahan Corridor at South Pamir. The volcanic sequence is mainly composed of phenocrysts- bearing basalt- andesites with minor rhyolite and volcaniclastic rock. Zircon U Pb ages reveal the basalt-andesite sequence erupted at 100–98 Ma. Bulk-rock geochemistry defines their potassic calc-alkaline signature and both their rock association and elemental geochemistry share most features of the continental arc volcanic sequences. On the other hand, they have variably enriched Nd isotope compositions with ε Nd (t) varying from −5.9 to −9.6, coupled with their enriched zircon Hf isotope signature with ε Hf (t) between −13 to −8. Whole-rock geochemistry and zircon oxygen isotope compositions (average δ 18 O = 7.74 ± 0.14) demonstrate that the primitive magma of the basalt-andesites were derived from partial melting of a metasomatized sub-continental lithospheric mantle and underwent variable assimilation fractional crystallization. Late Jurassic to Cretaceous volcanic-sedimentary sequences and coeval voluminous arc-like granodiorite and granites are widely distributed along the Southern Pamir. In the Central Pamir and further north, late Jurassic to Cretaceous sequences resemble features of back-arc basins. Taken together, we suggest that a northward low-angle or flat subduction of the Neo-Tethys Ocean along the Shyok zone was geodynamically related to the formation of the broad magmatic arc in South Pamir-Karakorum and the back-arc basins north of the South Pamir. • Arc-like Cretaceous basalt-andesite sequence in Southern Pamir (SP) erupted at ~100 Ma. • Architecture of the late Jurassic-Cretaceous arc-back-arc at Pamir was constructed. • Flat subduction of the Neo-Tethys Ocean produced the Cretaceous igneous rocks in SP.

Double-sided subduction with contrasting polarities beneath the Pamir-Hindu Kush: Evidence from focal mechanism solutions and stress field inversion

The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collision linked to two intra-continental subduction zones with different polarities. The seismicity and seismic tomography data show a steep northward subducting slab beneath the Hindu Kush and southward subducting slab under the Pamir. Here, we collect seismic catalogue with 3988 earthquake events to compute seismicity images and waveform data from 926 earthquake events to invert focal mechanism solutions and stress field with a view to characterize the subducting slabs under the Pamir-Hindu Kush region. Our results define two distinct seismic zones: a steep one beneath the Hindu Kush and a broad one beneath the Pamir. Deep and intermediate-depth earthquakes are mainly distributed in the Hindu Kush region which is controlled by thrust faulting, whereas the Pamir is dominated by strike-slip stress regime with shallow and intermediate-depth earthquakes. The area where the maximum principal stress axis is vertical in the southern Pamir corresponds to the location of a high-conductivity low-velocity region that contributes to the seismogenic processes in this region. We interpret the two distinct seismic zones to represent a double-sided subduction system where the Hindu Kush zone represents the northward subduction of the Indian plate, and the Pamir zone shows southward subduction of the Eurasian plate. A transition fault is inferred in the region between the Hindu Kush and the Pamir which regulates the opposing directions of motion of the Indian and Eurasian plates.

Muztaghata Dome Miocene Eclogite Facies Metamorphism: A Record of Lower Crustal Evolution of the NE Pamir

AbstractThe Pamir gneiss domes represent the most extensive exposure of mid to lower crustal rocks in the Himalayan‐Tibetan orogen north of the India‐Asia suture zone. Unlike other domes in the Central and Southern Pamir, the Muztaghata dome stands out due to its higher metamorphic grade, more complex structural elements, and variable timing of metamorphism. In order to unravel the P‐T‐t history of the Muztaghata dome and better constrain the timing of peak metamorphism, we applied petrologic modeling in concert with geochronology to samples from the structure. The Muztaghata gneiss dome is composed of a structurally higher metapelite‐dominated terrane in the west and a structurally lower orthogneiss terrane in the east. Our results from the western terrane indicate high‐pressure eclogite facies peak conditions of ~800°C/22 kbar at ~25–20 Ma. Zircon grains from metapelitic samples from the western terrane also yield Early Jurassic metamorphic U‐Pb ages with REE signals that indicate coeval garnet growth. Our results from the eastern terrane record high‐pressure amphibolite facies peak conditions of ~650°C/14 kbar at ~24–20 Ma, noticeably lower than the structurally higher western terrane indicating structural juxtaposition during Miocene exhumation. Peak metamorphic conditions from the eastern terrane indicate depths below the current Moho, supporting the interpretation that the Early Miocene Pamir crust was thicker than present. This was followed by rapid exhumation from depths of ~75–80 km and partial westward collapse of the Pamir after 20 Ma, possibly driven in part by regional lithospheric delamination.

Early Cretaceous granitoids in the Southern Pamir: Implications for the Meso-Tethys evolution of the Pamir Plateau

Although it is generally accepted that the Pamir was formed by long-term terrane drifting and accretion to the south margin of the Asia, the tectonic evolution during the Mesozoic remains unclear. The voluminous Cretaceous intrusions in the Southern Pamir-Karakorum provide key information for understanding the Mesozoic evolution in this region. In this contribution, we report detailed petrography, ages, mineral geochemistry, whole-rock elemental and SrNd geochemistry and in situ zircon LuHf isotopic compositions of the Early Cretaceous granitoids from the Chinese Wakhan Corridor, Southern Pamir. These granitoids are composed primarily of granodiorite and minor monzogranite and host dioritic enclaves. The granitoids were emplaced at 107–102 Ma, based on their zircon UPb ages. They have 63–73 wt% SiO2, Mg# between 39 and 53 and ACNK mostly lower than 1.1, and are I-type granites. The granitoids display arc-like geochemical signatures characterized by LREE-enriched patterns, variable negative Eu anomalies (LaN/YbN = 11.38–23.27; Eu/Eu* = 0.36–0.74), and a significant NbTa trough (Nb/La = 0.24–0.41). Isotopically, the granitoids have negative whole-rock εNd(t) (−8.73–7.35) and zircon εHf(t) (−17.7–5.3) values. The coeval dioritic enclaves (ca. 104 Ma) contain 57–63 wt% SiO2, and have high Mg# (46–57), low Cr (6.86–79.50 ppm), and Ni (2.88–10.00 ppm). These enclaves exhibit arc-like trace element patterns (Nb/La = 0.34–0.43) with variable negative Eu anomaly (Eu/Eu* = 0.52–0.87), uniform whole-rock εNd(t) (−4.74–4.73), and a large range of zircon εHf(t) values (−13.3–3.7). In line with their rock association and geochemistry, we suggest that the dioritic enclaves were derived from melting of a phlogopite-bearing mantle source modified by subduction-related process, followed by fractional crystallization and later assimilation by granitic hosts. These Early Cretaceous granitoids were most likely generated by partial melting of the Precambrian lower crust with variable involvement of mafic magma parental to the dioritic enclaves. Our new data, combined with the previous studies, reveal that the widespread Early Cretaceous magmatism in the Southern Pamir-Karakorum were most likely generated by flat-slab subduction of the Meso-Tethys Ocean during the Cretaceous.

Evidence for Late Triassic crustal suturing of the Central and Southern Pamir

The timing of closure of the Paleotethys and Rushan ocean basins and suturing of Gondwanan crustal fragments in the Pamir is not well resolved. Whereas the Central Pamir terrane is generally interpreted to have collided with the Northern Pamir terrane at the end of the Triassic, closure of the Rushan ocean and collision of the Southern Pamir terrane has been interpreted to be either broadly coeval (i.e., Late Triassic–Early Jurassic ~200 Ma) or have occurred significantly after closure of the Paleotethys in the Late Jurassic. New petrographic analyses and detrital zircon U-Pb data of the Lokzun Group Flysch and the terrigenous Darbasatash Group of the Southern Pamir terrane advocate for coeval terrane accretion of the Central and Southern Pamir terranes by the Latest Triassic. The Rhaetian Lokzun Group Flysch and the Early Jurassic Darbasatash Group have well-constrained stratigraphic ages and lie directly below and above a post-Cimmerian orogeny angular unconformity, respectively. Petrographic results for both successions indicate a recycled orogenic belt source, and detrital zircon age spectrum for both contain two prominent Phanerozoic age populations: an Early Silurian–Early Devonian (~440–408 Ma) and a Carboniferous Late Triassic (~350–222 Ma). These results suggest sediment was sourced from the Karakul-Mazar terrane, located in the northern Pamir, which requires closure of the Paleotethys and Rushan ocean basins and initial collision with the Central and Southern Pamir terranes by the end of the Late Triassic. Furthermore, these results suggest that the Northern Pamir terrane was topographically elevated relative to the surrounding terranes throughout the early Mesozoic.

Structure of crust and upper mantle beneath NW Himalayas, Pamir and Hindukush by multi-scale double-difference seismic tomography

The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017. The northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian plate under the Hindukush beyond 71°E longitude. The Indian plate overturns due south after interacting with the Asian plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian plate. The Asian plate is also imaged as a southward subducting seismic zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.

U-Pb ages of detrital zircon from Cenozoic sediments in the southwestern Tarim Basin, NW China: Implications for Eocene–Pliocene source-to-sink relations and new insights into Cretaceous–Paleogene magmatic sources

A detailed investigation of potential provenance is still lacking in the southwestern Tarim Basin, which restricts our complete understanding of Cenozoic source-to-sink relations between the basin interior and the Pamir salient - western Kunlun Mountain Range. Debate also exists concerning the potential sources of the Paleogene and Cretaceous igneous detritus present in the Cenozoic sedimentary sequences. Here, we present U-Pb (LA-ICP-MS) ages of detrital zircons from the continuous Eocene-Pliocene sediment series in the well-exposed Aertashi section to investigate changes in sediment provenance through time. The U-Pb detrital zircon ages range widely from 45 to 3204 Ma and can be divided into seven main groups: 45–65 Ma (sub-peak at 49 Ma), 67–103 Ma (sub-peak at 95 Ma), 196–251 Ma (sub-peak at 208 Ma), 252–416 Ma (sub-peak at 296 Ma), 417–540 Ma (sub-peak at 446 Ma), 550–1429 Ma (sub-peaks at 614 Ma, 828 Ma and 942 Ma) and 1345–3204 Ma (sub-peaks at 1773 Ma and 2480 Ma). These zircons were mainly derived from the western Kunlun Mountain Range and northern Pamir salient to the west and south. The evolution of the provenance and source-to-sink relationship patterns in the southwestern Tarim Basin can be divided into three stages: (1) The Middle Eocene to Lower Oligocene sediments display a wide variety of detrital zircon ages, suggesting that the source area was extensive. (2) A major change in provenance occurred during the Late Oligocene to Early Miocene and was characterized by an abrupt increase in the proportion of Triassic and Lower Paleozoic igneous components, implying a significant adjustment in topography induced by the initial uplift and exhumation of the western Kunlun Mountain Range and northern Pamir salient. (3) In the Late Miocene, the source-to-sink system transformed again, and contributions of Triassic to Lower Paleozoic material weakened substantially due to the sufficient indentation of the Pamir salient. Our integrated analyses of zircon geochronology indicate that the main source terranes of the Paleogene and Cretaceous igneous detritus are the central and southern Pamir salient, respectively, which are speculated to have been continuously connected to the study area during Eocene-Pliocene times, although such detritus is scarce in certain formations and has not yet been detected.

Pamir Plateau formation and crustal thickening before the India-Asia collision inferred from dating and petrology of the 110–92 Ma Southern Pamir volcanic sequence

The formation of the Pamir is a key component of the India-Asia collision with major implications for lithospheric processes, plateau formation, land-sea configurations and associated climate changes. Although the formation of the Pamir is traditionally linked to Cenozoic processes associated with the India-Asia collision, the contribution of the Mesozoic tectonic evolution remains poorly understood. The Pamir was formed by the suturing of Gondwanan terranes to the south margin of Eurasia, however, the timing and tectonic mechanisms associated with this Mesozoic accretion remain poorly constrained. These processes are recorded by several igneous belts within these terranes, which are not well studied. Within the Southern Pamir, the Albian-Turonian volcanic rocks and comagmatic plutons of the Kyzylrabat Igneous Complex (KIC) provide an important and still unconstrained record of the Pamir evolution. Here we provide the age, origin and the geodynamic setting of the KIC volcanics by studying their petrology, zircon U-Pb geochronology, geochemistry and isotope composition. 17 samples from the KIC volcanics yield U-Pb ages spanning from 92 to 110Ma. The volcanics are intermediate to acidic in composition (SiO2=56–69wt%) and exhibit high-K calc-alkaline and shoshonitic affinity (K2O/Na2O=1–2.2wt%). They show enrichment in LILE and LREE and depletion in HFSE and HREE with negative Ta, Ti and Nb anomalies, suggesting an arc-related tectonic setting for their formation. Low εNd(t) values (from −9.1 to −4.7), relatively high 87Sr/86Sr(i) ratios (0.7069–0.7096) and broad range of zircon εHf values (from −22.6 to −1.5) suggest a mixture of different magma sources. These features suggest that volcanics were derived by crustal under- or intraplating of an enriched subduction-related mantle shoshonitic magmas, by heating and partial melting of the lower crust, and by mixing of both magma components. Our results further imply that the KIC volcanics represent a shoshonitic suite typical of an evolution from active continental arc to post-collisional setting with a steepening of the Benioff zone and thickening of the crust toward the back-arc. This setting is best explained by the subduction - collision transition along the Shyok suture due to accretion of the Kohistan island arc to the Karakoram. This suggests that a significant part of the crustal shortening and thickening accommodated in the Pamir occurred in the Mesozoic before the India-Asia collision with implications for regional tectonic models. This further suggests the Pamir was already a major topographic feature with potentially important paleoclimate forcing such as the monsoonal circulation.

Bridging Glaciological and Hydrological Trends in the Pamir Mountains, Central Asia

With respect to meteorological changes and glacier evolution, the southern Pamir Mountains are a transition zone between the Pamirs, Hindu Kush and Karakoram, which are water towers of Central Asia. In this study, we compare runoff and climate trends in multiple time periods with glacial changes reported in the literature. Recent glacier evolution in the Southern Pamirs and its contribution to river runoff are studied in detail. Uncertainties of estimating glacier retreat contribution to runoff are addressed. Runoff trends in the Pamir-Hindu Kush-Karakoram region appear to be a strong proxy for glacier evolution because they exhibit the same spatial pattern as glacial change. There is an anomaly in the North-West Pamirs and Northern Karakoram, showing decreasing runoff trends. In the opposite way, there is a glacier and hydrological change experienced in the Southern Pamirs and Hindu Kush. The prevailing hypothesis for the Karakoram Anomaly, decreasing summer temperatures along with increasing precipitation rates, seems to be valid for the North-Western Pamirs, as well. In the Southern Pamirs, temperature trends have been rising since 1950. Here, the unique water cycle of exclusively winter precipitation does not protect glaciers from accelerated retreat. Snow cover is preset to melt within the seasonal water cycle, due to much lower precipitation amounts falling on glaciers. Therefore, a probable increase in westerly precipitation in both regions causes glacier mass gain in the Northern Pamirs and rising river flows in the Southern Pamirs.

On the role of contamination and hybridism in formation of the composite Raumid pluton granites (Pamir Mnts.): Results of Sm–Nd Isotope Study

This work presents isotope Sm-Nd data obtained for bulk samples of granites of all 8 emplacement phases of the Raumid granite massif, which occurred 35 Ma ago at a hypabyssal depth during the orogenic stage of development of Southern Pamir fold system. The 147Sm/144Nd ratio in studied collection of granite samples ranges between 0.091 and 0.323; the eNd(T) value is–4.0. The Sm-Nd isotope study results suggest that all granite varieties distinguished in the Raumid massif are comagmatic formations and contamination and hybridization processes did not play any role in REE distribution in granites. At this, the source of parental magma did not change during granite generation. We assume that the only process, resulted in the trace element evolution in granites, was differentiation of three batches of magma sequentially uplifted from the source.

Multisystem dating of modern river detritus from Tajikistan and China: Implications for crustal evolution and exhumation of the Pamir

The Pamir is the western continuation of Tibet and the site of some of the highest mountains on Earth, yet comparatively little is known about its crustal and tectonic evolution and erosional history. Both Tibet and the Pamir are characterized by similar terranes and sutures that can be correlated along strike, although the details of such correlations remain controversial. The erosional history of the Pamir with respect to Tibet is significantly different as well: Most of Tibet has been characterized by internal drainage and low erosion rates since the early Cenozoic; in contrast, the Pamir is externally drained and topographically more rugged, and it has a strongly asymmetric drainage pattern. Here, we report 700 new U-Pb and Lu-Hf isotope determinations and >300 40Ar/39Ar ages from detrital minerals derived from rivers in China draining the northeastern Pamir and >1000 apatite fission-track (AFT) ages from 12 rivers in Tajikistan and China draining the northeastern, central, and southern Pamir. U-Pb ages from rivers draining the northeastern Pamir are Mesozoic to Proterozoic and show affinity with the Songpan-Ganzi terrane of northern Tibet, whereas rivers draining the central and southern Pamir are mainly Mesozoic and show some affinity with the Qiangtang terrane of central Tibet. The εHf values are juvenile, between 15 and −5, for the northeastern Pamir and juvenile to moderately evolved, between 10 and −40, for the central and southern Pamir. Detrital mica 40Ar/39Ar ages for the northeastern Pamir (eastern drainages) are generally older than ages from the central and southern Pamir (western drainages), indicating younger or lower-magnitude exhumation of the northeastern Pamir compared to the central and southern Pamir. AFT data show strong Miocene–Pliocene signals at the orogen scale, indicating rapid erosion at the regional scale. Despite localized exhumation of the Mustagh-Ata and Kongur-Shan domes, average erosion rates for the northeastern Pamir are up to one order of magnitude lower than erosion rates recorded by the central and southern Pamir. Deeper exhumation of the central and southern Pamir is associated with tectonic exhumation of central Pamir domes. Deeper exhumation coincides with western and asymmetric drainages and with higher precipitation today, suggesting an orographic effect on exhumation. A younging-southward trend of cooling ages may reflect tectonic processes. Overall, cooling ages derived from the Pamir are younger than ages recorded in Tibet, indicating younger and higher magnitudes of erosion in the Pamir.