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Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnet-bearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610–690 °C and 6.5–10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720–750 °C and 13.4–14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630–730 °C and 3.8–7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438–398 Ma.

The final subduction and suture of the Paleo-Asia Ocean (PAO) are controversial, and the key to this question is to locate the latest subduction/final suture of the accretionary type orogenic belt. Previous studies mainly focused on the Tianshan, Beishan, Alxa, and Solonker Orogens for this issue. As a Phanerozoic orogenic belt located further south of the Beishan-Alxa Tectonic Belts, the Dunhuang Orogenic Belt (DOB) is becoming a research hotspot for revealing the evolutionary history of the southernmost Central Asia Orogenic Belt (CAOB). The youngest subduction-related arc magmatism is pivotal for constraining the lower limit of subduction of a lost ocean. This study presents integrated investigations of field observation, whole-rock geochemistry, and geochronology, targeting diabase dykes, intermediate-acid magmatic rocks, and garnet-bearing metabasite samples in the middle part of the DOB. LA-ICP-MS U-Pb dating of zircon yielded episodic magmatism of ca. 274–273 Ma for Xiaohongshan granite and Dongbatu syenogranite, ca. 250 Ma for Keziletage syenite, ca. 243–239 Ma for diabase and granitic dykes in the Kalatashitage area and Mogutai syenogranite, and maximum deposition age of ca. 262 Ma for pyroclastic rock in the Kalatashitage area. Most of those Permian-Triassic magmatic rocks show continental arc-related geochemical features during the subduction stage. The negative εHf(t) values and ancient TDM2 model ages of zircon indicate they were mainly derived from the partial melting of ancient crustal materials. The hornblende 40Ar/39Ar ages of ca. 258–250 Ma of the garnet-bearing metabasite samples also reflect a high heat flow setting during this period possibly triggered by arc activities. These Permian-Triassic magmatic and thermal records in the DOB are similar to contemporaneous records in surrounding South Tianshan-Alxa-Beishan orogens. We suggest that the final subduction of the PAO in the DOB possibly at least lasted to the Middle Triassic. [ABSTRACT FROM AUTHOR]

Competing Interests: Conflict of interest The authors declare that they have no conflict of interest.

Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnet-bearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610-690 °C and 6.5-10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720-750 °C and 13.4-14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630-730 °C and 3.8-7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438-398 Ma. [ABSTRACT FROM AUTHOR]

The Duobagou Permian–Triassic granites of the Dunhuang orogenic belt are of great importance in understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt. LA-ICP-MS U–Pb zircon ages indicate that Permian–Triassic granitic intrusions from the Duobagou area formed at 276–274 Ma and 246 ± 1 Ma. These granites have high SiO2, Na2O and K2O, but low Al2O3, CaO and MgO contents and belong mainly to the high-K calc-alkaline I-type granite series. Based on whole-rock geochemistry and Sr–Nd and zircon Hf isotopes, the Duobagou Permian–Triassic granites were dominantly derived from the partial melting of lower continental crust formed during late Palaeoproterozoic to Mesoproterozoic times in a post-collisional extensional setting. Permian granites with zircon ϵHf(t) values of −5.4 to +3.1 and Hf model ages of TDM2 = 1.14–1.70 Ga indicate the involvement of a mantle component in their petrogenesis. Triassic granites with higher zircon ϵHf(t) values (+0.5 to +3.8) and TDM2 = 1.08–1.31 Ga suggest more juvenile sources caused by a greater contribution of mantle-derived melts, indicating a significant crustal growth. Regional extension from lithospheric delamination and heating from asthenospheric upwelling were proposed to have triggered the partial melting of lower crust, resulting in the generation of the Permian–Triassic magmatism. This may have been the mechanism for the significant crustal growth during Permian and Triassic times in the southernmost Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwest China. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure-temperature (P-T) paths were retrieved, indicative of metamorphism of a possible subduction environment. Peak metamorphic P-T conditions (790~920 °C/28~41 kbar) of garnet clinopyroxenite suggest that they experienced high pressure to UHP metamorphism, and the UHP metamorphism occurred in the coesite- or diamond-stability field. The UHP metamorphic event is further confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from within the garnet. SIMS U-Pb dating of metamorphic titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian (~ 389~370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this orogen in the Paleozoic. It can be further inferred that most of the UHP rocks of this orogen are now buried in the depth. [ABSTRACT FROM AUTHOR]

Garnet-bearing mafic granulites and amphibolites from the Hongliuxia area of the southern Dunhuang orogenic belt, northwestern China, commonly occur as lenses or boudinages enclosed within metapelite or marble, which represent the block-in-matrix feature typical of orogenic mélange. Three to four generations of metamorphic mineral assemblages are preserved in these rocks. In the high-pressure amphibolites, prograde mineral assemblages (M1) occur as inclusions (hornblende + plagioclase + quartz ± chlorite ± epidote ± ilmenite) preserved within garnet porphyroblasts, and formed at 550–590 °C and 7.7–9.2 kbar based on geothermobarometry. The metamorphic peak mineral assemblages (M2) are composed of garnet + hornblende + plagioclase + quartz + clinopyroxene, as well as titanite + zircon + rutile + apatite as accessory minerals in the matrix, and are estimated to have formed at 640–720 °C and 14.1–16.0 kbar. The first retrograde assemblages (M3) are characterized by “white-eye socket” symplectites (hornblende + plagioclase + quartz ± biotite ± epidote ± magnetite) rimming garnet porphyroblasts, which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under P – T conditions of 610–630 °C and 5.6–11.8 kbar. The second retrograde assemblages (M4) are intergrowths of actinolite and worm-like quartz produced by the breakdown of the matrix hornblendes, and formed under P – T conditions of ∼490 °C and ∼2.8 kbar. For the high-pressure mafic granulites, the prograde assemblages (M1) are represented by plagioclase + quartz preserved within the garnet porphyroblasts. The metamorphic peak assemblages (M2) are garnet + matrix minerals (clinopyroxene + plagioclase + quartz + hornblende + rutile + zircon) and were estimated to have formed at ∼680 °C and ∼15.4 kbar. The retrograde assemblages (M3) are characterized by fine-grained patches of hornblende + plagioclase + quartz rimming the garnet porphyroblasts, as well as hornblende rimming clinopyroxene in the matrix, and were inferred to have formed at ∼620 °C and ∼4.2 kbar. For the metapelitic gneiss, the metamorphic peak assemblages are the garnet porphyroblasts plus the matrix minerals (biotite + plagioclase + quartz + ilmenite + zircon), which were estimated to have formed at ∼630 °C and ∼8.9 kbar. The mafic granulites and amphibolites record fairly similar clockwise P–T paths that include nearly isothermal decompression processes, which suggest that they experienced subduction and subsequent rapid tectonic exhumation. SIMS and LA-ICP-MS U–Pb dating of zircons and 40Ar/39Ar dating of hornblende suggest that the metamorphism occurred at ∼430–390 Ma. Field occurrences, different protolith ages of the mafic granulites and amphibolites, and the considerable gap in peak P – T conditions between the amphibolite and mafic granulite boudinages and their country rock may suggest a mélange accumulation process during the Paleozoic caused by the Silurian–Devonian orogeny, which is possibly associated with the closure of the Liuyuan ocean, a branch of the Paleo-Asian ocean near the southern Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

Mafic granulite and amphibolite in the Dongbatu and Mogutai blocks, middle Dunhuang orogenic belt, northwest China, southernmost Central Asian orogenic belt, occur as lenses within the matrix of metapelite and marble, exhibiting typical block-in-matrix fabrics of tectonic mélange. Three stages of metamorphic mineral assemblages were identified in these lenses. Clockwise metamorphic pressure-temperature (P-T) paths were obtained through geothermobarometry and thermodynamic pseudosection modeling, passing from 656 °C and 10.9 kbar through 830 °C and 16.5 kbar to 657 °C and 4.9 kbar for the mafic granulite, and from 564-645 °C and 3.2-9.6 kbar through 634-727 °C and 6.1-14.2 kbar to 615-664 °C and 3.2-4.2 kbar for the amphibolites, respectively. Metamorphic peak P-T conditions in the metapelitic country rocks were estimated to be 635-675 °C and 6.0-6.9 kbar. The metamorphic peak of the mafic granulite approaches the high P-T facies series, indicative of a subduction zone. Secondary-ion mass spectrometry and laser ablation- inductively coupled plasma-mass spectrometry U-Pb dating of metamorphic zircons suggests that the metamorphic event occurred between ca. 420 and 372 Ma. These data further certify that the subduction of the continental margin and subsequent uplift of the Dunhuang orogenic belt represent a longlived tectono-metamorphic event in the Paleozoic. [ABSTRACT FROM AUTHOR]

Banded iron formations (BIFs), granites and diabases are extensively distributed in the Kuluketage block of the northeast Tarim Craton. Here we report laser ablation–inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) zircon U–Pb ages and whole‐rock elemental data for these rocks. The detrital zircons from the BIFs show a peak age of 2.0–1.8 Ga with a weighted mean age of 1945 ± 10 Ma (MSWD = 0.77), and the zircons from the granite give an upper intercept age of 1974 ± 27 Ma (MSWD = 1.05). The trace element features suggest that the Asitingbulake granite, which belongs to the I‐type granite, may originate from the re‐melting of continental crust in a ~1.95 Ga collisional orogenic setting. Recently, the 2.0–1.8 Ga continuous magmatic and metamorphic events which are contemporaneous with the global orogenic event have been reported in the Kuluketage block and other massifs around the Tarim Craton (e.g. Central Tianshan, Dunhuang, Quanji, Altyn Tagh, West Kunlun). Based on the previous geochronological data, two 2.0–1.8 Ga orogens associated with the assembly of the Columbia supercontinent can be identified along the north and south margins of Tarim Craton: (1) the north Tarim Orogen, Central Tianshan–Kuluketage–Dunhuang orogenic belt and (2) the south Tarim Orogen, West Kunlun–Altyn Tagh–Aketashtage–Quanji orogenic belt. Additionally, this paper reports a new zircon U–Pb age of 1497 ± 21 Ma (MSWD = 0.96) from the Baowenbulake diabase dykes where the trace element features suggest that the parental magma of Baowenbulake diabases is derived from the mantle in an intra‐plate rifting or extensional setting. The ~1.5 Ga diabases from northwest Tarim corresponded to a major episode of mafic magmatism during the early Mesoproterozoic period identified in other crustal fragments of Laurentia, Siberia, Greater Congo, South China and North China Craton and probably belong to one of the three major large igneous provinces associated with the breakup of the Mesoproterozoic Columbia supercontinent. The data from this paper provide important constraints on the configuration of the Tarim Craton during the assembly and breakup of the Columbia supercontinent. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

While the western part of northern Tarim Craton has long been considered as a Paleozoic passive margin, a pronounced Silurian‐Devonian magmatism developed on eastern part of this margin may indicate different but active margin setting. In this contribution, detailed structural mapping, petro‐structural analysis, and geochronological investigations were conducted in the Korla area, eastern part of northern Tarim Craton. Three main generations of fabrics were recognized. The earliest pervasive fabric is an originally sub‐horizontal metamorphic S1 foliation that is in part associated with migmatization characterized by high temperature/low pressure metamorphic mineral assemblages, interpreted as reflecting crustal extension. S1 foliation was affected by D2 contraction forming regional‐scale F2 upright folds associated with sub‐vertical axial planar foliation S2. D3 is marked by development of NW‐SE oriented dextral fault, asymmetric mega‐folding of S2 and spaced NW‐SE‐striking S3 foliation, likely in response to dextral transpression. Geochronological data indicate that D1 extension occurred from ca. 420 to 410 Ma, D2 contraction started around 410 Ma and lasted till 400 Ma or later, and D3 transpression was ongoing around ∼370 Ma. Integrated with regional data, an updated geodynamic model is proposed by interpreting the Central Tianshan, South Tianshan and NE Tarim Craton as an early Paleozoic supra‐subduction system. We suggest that the Silurian‐Devonian event reflects thermal softening and horizontal stretching of the supra‐subduction crust, resulting in drifting of the Central Tianshan continental arc from the proto Tarim Craton in association with opening of the South Tianshan back‐arc basin in‐between. Key Points: NE Tarim Craton formed a sub‐horizontal HT/LP foliation in response to crustal extension in the late Silurian‐early DevonianThinned and thermally softened northern Tarim margin was affected by middle Devonian shorteningEarly Paleozoic northern Tarim, South Tianshan, and Central Tianshan evolved into one supra‐subduction environment [ABSTRACT FROM AUTHOR]

Basin evolution along the northeastern Tibetan Plateau related to the Altyn Tagh Fault (ATF) has significant implications for deciphering the formation of the Tibetan Plateau. However, the Mesozoic history of the ATF is still not well understood. In this contribution, we present a comprehensive sedimentologic and provenance analysis of the Jurassic Dunhuang Basin (DHB) to reconstruct the basin prototype and evolution and to discuss the early history of the ATF. The basin infill consists of late‐Early through Late Jurassic sediments interbedded with basalt, which were deposited in alluvial to lacustrine environments during the Early to Middle Jurassic, and in fluvial to fan delta environments during the Late Jurassic. The analyses of gravel component, paleocurrent and detrital zircon U‒Pb geochronology indicate that the clastic sediments were mainly derived from peripheral areas of the Bei Shan (north), Altyn Tagh—Qilian Shan (south), and the internal Sanwei Shan. Combined with seismic reflection data interpretations, our results suggest that rifting started by the activation of bilateral boundary faults during the Early Jurassic. This was followed by extension and associated magmatism due to subcrustal ductile necking and increased heat flux during the Middle Jurassic, and by final transformation into subsidence sag related to boundary fault die‐out or weakening during the Late Jurassic. We conclude that the DHB formed in an extensional setting generated by the far‐field effects of the Bangong‐Nujiang Ocean closure during the Jurassic, and that the ATF consisted of three subordinate normal faults rather than a sinistral strike‐slip fault during the Jurassic. Plain Language Summary: To understand the Cenozoic rise of Tibetan Plateau, one should pay special attention to the associated Mesozoic basin evolution and its mechanisms. We investigated the Jurassic development of the Dunhuang basin (DHB) by analyzing its stratigraphy, sedimentary facies, and sources. We reconstructed the evolution history of the basin and its Early Jurassic initiation in association with movements along the Altyn Tagh Fault (ATF). Subsequent extension along with increased heat flux during the Middle Jurassic was followed by transformation into subsidence sag in the Late Jurassic. Our results suggest that the DHB formed in an extensional rather than a strike‐slip structural setting, and that there was not sinistral movement along the ATF during Jurassic. Key Points: Dunhuang Basin was infilled with the late‐Early to Late Jurassic fluvio‐lacustrine sediments, with sources from nearby mountainsBasin formed in an Early to Middle Jurassic extensional settings, followed by Late Jurassic flexural subsidenceAltyn Tagh Fault was a system of normal faults with no sinistral movements during Jurassic [ABSTRACT FROM AUTHOR]

Subduction‐related dehydration and exhumation‐related rehydration play an important role in water recycling on Earth. Water can be transported to the deep mantle through crustal subduction, whereas the behavior of water in the subducted crust during exhumation remains enigmatic. Here, we use an integrated micro X‐ray fluorescence spectrometry, transmission terahertz time‐domain, thermogravimetry, and differential scanning calorimetry approach for the first time on high‐pressure mafic granulite and amphibolite to investigate the water species and contents, as well as exhumation rehydration reactions. Our study demonstrates that garnet, hornblende, and ilmenite contain considerable amounts, and plagioclase contains minor amounts of water as molecular and structural species, whereas quartz contains only a minor amount of structural water. Water released from garnet and external fluids from the grain boundary will either migrate into hornblende, plagioclase, ilmenite, and quartz, or stored in the mantle wedge, or further subducted into the deep mantle. We suggest that water recycling between the Earth's surface and deep mantle is an unequilibrium process, and the lower crust and mantle may store a significant amount of water in deep Earth and can function as a container to feed and maintain the water recycling balance. Plain Language Summary: High‐pressure mafic granulites, representing rocks that underwent granulite facies metamorphism under high temperatures and pressures, are potential proxies to examine water recycling between Earth's surface and deep mantle layers through subduction zone channels. During metamorphism, water can be transported into the deep mantle via subduction‐related dehydration and returned to the surface through exhumation‐related rehydration processes, resulting in the formation of anhydrous and hydrous minerals in high‐pressure mafic granulites and amphibolites. The high‐pressure mafic granulite and amphibolite from the northern margin of the North China Block experienced the subduction of the Paleo‐Asian Ocean and the exhumation process of the subducted crust. In this study, we investigate the water species and content changes among the anhydrous and hydrous minerals, as well as whole‐rock during the exhumation process. We find that anhydrous mineral can store a considerable amount of water and release it into the hydrous minerals through rehydration reaction during exhumation. We propose that high‐pressure mafic granulite performing as a water carrier is able to transport significant amounts of water from deep mantle to the Earth's surface. Our study provides new insights for retrieving water recycling information in the deep Earth. Key Points: Hornblende, garnet, and ilmenite can store significant amounts of water, but only minor amounts in plagioclase and quartzHigh‐pressure granulite may be an important water carrier and is able to facilitate water recycling in deep EarthTransmission terahertz time‐domain spectroscopy offers a novel approach for water species and content detection in natural rocks [ABSTRACT FROM AUTHOR]

The Tarim Craton (or Tarim Block) is geographically located in the Northwest of China and tectonically between the Central Asian Orogenic Belt (CAOB) to the north and the Tethys to the south, which underwent a secular Precambrian evolution history from Ecoarchaean to Ediacaran. Owing to its marginal positions both in the Columbia (or Nuna) and Rodinia supercontinent configurations, it could play a key role in understanding the geodynamics of the assembly and break-up of the Precambrian supercontinents. This paper aims to present a critical review on the comprehensive synthesis of the Tarim Craton, detailing the Precambrian evolution processes and discussing its coupling with the Precambrian supercontinents. The Tarim Craton shows a typical plateform-like and double-layered structure, comprising the pre-middle Cryogenian basement with the middle Cryogenian-Ediacaran cover sequence. During its protracted basement evolution, diverse types and multiple stages of pre-Ediacaran intrusions were emplaced in the basement. Since Pleoproterozoic to early Cryogenian, crust reworking, rather than juvenile crust addition, played a key role in the final cratonization of its basement. Despite the final cratonization of the Tarim completed in the middle Cryogenian, both the bulk-rock Sm-Nd and zircon Lu-Hf isotope compositions demonstrated that its crust mainly formed in Archaean. Its characteristics of sedimentary features, metamorphic temporal-spatial architecture, the multiple phases and diverse types of intrusions reveal that the Tarim Craton is possibly composed of two main terranes with distinct features, i.e. the Northern Tarim Terrane (NTT) and the Southern Tarim Terrane (STT). It has been suggested that the STT could be a continental fragment that has drifted from West Africa, while the NTT shows a significant affinity with the India–North China Craton before Calymmian. Both were involved in the assembly and break-up of the Columbia supercontinent, and amalgamated during the assembly of the Rodinia. At the same time, it docked at the northern margin of Australia in the middle Cryogenian. Nevertheless, the subduction along the northern margin of the NTT continued at least until ca. 760 Ma. The voluminous 820–760 Ma diverse-type intrusions in the NTT have been ascribed to a genetic relation in the interaction between the circum-Rodinia subduction and the Rodinian superplume. The upwelling of the Rodinian superplume terminated the long-lasting subduction along the northern margin of the Tarim Craton. Since 740 Ma, being consistent with the break-up of the Rodinia, the Tarim Craton started drifting from the Rodinia supercontinent. The transition from signature to the passive continental margin of the middle Cryogenian-Ediacaran (for its cover sequences) rules out the possibility of the circum subduction along its northern margin lasting to early Palaeozoic. Additionally, with the Rodinia breaking up into the assembly of the Gondwana, the Tarim Craton, together with other continents in Eastern Asia, had docked at the margin of the Eastern Gondwana in early Palaeozoic. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Metamorphic sole rocks of the Pınarbaşı Ophiolite are one of the best-preserved rock units observed along the Tauride Ophiolite Belt in Turkey. The metamorphic sole rocks observed as tectonic slices at the base of mantle tectonites as well as blocks in the mélange units consist mainly of garnet-clinopyroxene-amphibolite, garnet-amphibolite, amphibolite, epidote-amphibolite, quartz-amphiboleschist and metabasalt. The amphibolites display a wide range of geochemical signatures such as those of N-MORB, E-MORB, OIB and IAT. The metabasalts exhibit OIB geochemical characteristics. P-T estimates indicate that the garnet-clinopyroxene-amphibolites reached peak metamorphic conditions of 790-840 °C and 12-14 kbar. High-grade metamorphism is followed by a stage of decompression, which is indicated by the presence of symplectitic growth of amphibole and plagioclase over garnet in garnet-clinopyroxene-amphibolites. P-T estimates for garnet-clinopyroxene-amphibolites suggest that they were metamorphosed under granulite-facies conditions (ca. 35-40 km). High temperature estimated from granulite facies rocks should be ascribed to the occurrence of the sole rocks during the inception of the intra-oceanic subduction, beneath young or relatively hot oceanic lithosphere. On the other hand, mineral paragenesis of the metabasalts suggest greenschist facies metamorphic conditions. Protoliths of the metabasalts were probably metamorphosed during final stages of subduction where they were very close to sea floor as the subduction zone was probably clogged by a seamount. The greenschist- and granulite-facies sole rocks were metamorphosed probably beneath the hot oceanic lithosphere at different depths of the subduction zone. Considering all these data are important to better understanding intra-oceanic subduction and final obduction events of the Tethys Ocean. [ABSTRACT FROM AUTHOR]

High‐pressure (HP) granulites form either in the domain of the subducted plate during continental collision or in supra‐subduction systems where the thermally softened upper plate is shortened and thickened. Such a discrepancy in tectonic setting can be evaluated by metamorphic pressure–temperature–time‐deformation (P–T–t–D) paths. In the current study, P–T–t–D paths of Early Palaeozoic HP granulite facies rocks, in the form of metabasic lenses enclosed in migmatitic metapelite, from the Dunhuang block, NW China, are investigated in order to constrain the nature of the HP rocks and shed light on the geodynamic evolution of a modern hot orogenic system in an active margin setting. The rocks show a polyphase evolution characterized by (1) relics of horizontal or gently dipping fabric (S1) preserved in cores of granulite lenses and in garnet porphyroblasts, (2) a N‐S trending sub‐vertical fabric (S2) preserved in low‐strain domains and (3) upright folds (F3) associated with a ubiquitous steep E‐W striking axial planar foliation (S3). Garnet in the granulites preserves relics of a prograde mineral assemblage M1a equilibrated at ~11.5 kbar and ~770–780°C, whereas the matrix granulite assemblage (M1b) from the S1 fabric attained peak pressure at ~13.5 kbar and ~850°C. The granulites were overprinted at ~8–11 kbar and ~850–900°C during crustal melting (M2) followed by partial re‐equilibration (M3) at ~8 kbar and ~625°C. A garnet Lu–Hf age of 421.6 ± 1.2 Ma dates metamorphism M1, while a garnet Sm–Nd age of 385.3 ± 4.0 Ma reflects M3 cooling of the granulites. The mineral assemblage, M1, of the host migmatitic metapelite formed at ~9–12.5 kbar and ~760–810°C, partial melting and migmatization (M2) occurred at ~7 kbar and ~760°C and re‐equilibration (M3) at ~5–6 kbar and ~675°C. A garnet Lu–Hf age of 409.7 ± 2.3 Ma dates thermal climax (M2) and a garnet Sm–Nd age of 356 ± 11 Ma constrains M3 for the migmatitic metapelites. The timing of this late phase is also bracketed by an emplacement age of syntectonic granite dated at c. 360 Ma. Decoupling of M1 and M2 P–T evolutions between the mafic granulites and migmatitic metapelites indicates their different positions in the crustal column, while the shared pressure–temperature (P–T) evolution M3 suggests formation of a mélange‐like association during the late stages of orogeny. The high‐pressure event D1‐M1 is interpreted as a result of Late Silurian–Early Devonian moderate crustal thickening of a thermally softened and thinned pre‐orogenic crust. The high‐temperature (HT) re‐equilibration D2‐M2 is interpreted as a result of Mid‐Devonian shortening of the previously thickened crust, possibly due to 'Andean‐type' underthrusting. The D3‐M3 event reflects Late Devonian supra‐subduction shortening and continuous erosion of the sub‐crustal lithosphere. This tectono‐metamorphic sequence of events is explained by polyphased Andean‐type deformation of a 'Cascadia‐type' active margin, which corresponds to a supra‐subduction tectonic switching paradigm. [ABSTRACT FROM AUTHOR]

Corundum is rarely found in situ within alkali syenites. A corundum-bearing syenite was found in the Yushishan rare metal deposits of the eastern section of the Altyn Tagh fault in the northeastern Tibetan Plateau, but the characteristics and formation of corundum remain unknown. We describe a corundum-bearing syenite dike emplaced in biotite plagioclase gneiss that suffered overprinted deformation with characteristics of mylonitization. The corundum crystals have variable grain sizes, and the largest ones are megacrystic with growth zoning. The corundum crystals contain a variety of mineral inclusions that are divided into primary and secondary. The primary mineral inclusions within the corundum include variable contents of Fe-Ti oxide needles, ilmenite, zircon, monazite-(Ce), potassium feldspar, pyrochlore, columbite-(Fe), magnetite, samarskite-(Y), and pyrite that indicate corundum crystallized in peraluminous Zr-rich and Si-poor alkali rock with variable TiO2 contents. Secondary mineral inclusions include Zn-rich hercynite, ilmenite, magnetite, annite, fluorapatite, and intergrowths of ilmenite with columbite-(Fe) and goethite that reveal late-stage influx of Zn-, Ti-, Fe-, and F-bearing fluids into corundum that caused metasomatism and element migration and mineral precipitation. The trace element analysis of corundum shows high-Fe and -Ga contents and low-Mg and -Cr contents that are consistent with the characteristics of corundum of magmatic origin. The trace element characteristics and the oxygen isotopes (6.2–8.2‰) results indicate that corundum crystallized in melts with the involvement of Al-rich and Si-poor crustal material. [ABSTRACT FROM AUTHOR]

The Dunhuang region is located in the east of the Tarim Craton and has long been considered as part of a Precambrian terrane of the Tarim or North China Craton. Aiming to further understand the tectonic evolution of the Dunhuang region and its relations with the adjacent tectonic units, this study is to investigate the metamafic rocks in the Sanweishan area, Dunhuang region, and in turn to summarize the tectono-thermal events and re-examine the tectonic characteristics of the region. The metamafic rocks in the Sanweishan area include three types of amphibolites. They are garnet–clinopyroxene amphibolites, garnet-free amphibolites and garnet–mica amphibolites. The whole-rock major and trace element compositions suggest that their protoliths probably are E-MORB type tholeiitic basalts with some crustal addition. The LA-ICP-MS zircon U–Pb data of the garnet–clinopyroxene amphibolite and the garnet-free amphibolite yielded lower intercept ages of 410 ± 11 Ma and 403 ± 8 Ma, respectively, while the garnet–mica amphibolite gave three metamorphic ages of 441 ± 3 Ma, 408 ± 12 Ma and 370 ± 2 Ma. Three suites of metamorphic conditions have been estimated at 1.14–1.55 Gpa and 458–548 °C, 0.67–0.82 Gpa and 590–600 °C, and 0.47–0.66 Gpa and 557–586 °C for garnet–clinopyroxene amphibolite, using different mineral thermobarometers, which illustrate a collisional orogeny-related clockwise P–T path. Integrated with the study on the high-pressure granulite in the Mogutai area, it can be inferred that the metamafic rocks in the Sanweishan area obviously experienced amphibolite–facies metamorphism at ca. 410–400 Ma, and they could also underwent high-grade metamorphism at ca. 440–430 Ma. Therefore, we suggest that the E–W-trending collisional orogeny of ca. 440–400 Ma could sweep cross the Dunhuang region. The Dunhuang region records multiple tectono-thermal events occurring at ca. 3.1–2.5 Ga, ca. 2.3–1.6 Ga, ca. 440–400 Ma and ca. 370–310 Ma. However, compared with the limited exposure of the Precambrian complex, the Early Silurian–Late Carboniferous (ca. 440–310 Ma) orogeny-related metamorphic and magmatic rocks are widely distributed in the Dunhuang region, making up nearly 70% of the total exposure. Thus, it is proposed that the geological bodies in the Dunhuang region were mainly produced by a Paleozoic orogeny and represent a Paleozoic orogen, while the limited Precambrian complex probably is a microcontinental fragment or part of the margin of the Tarim or North China Cratons that was involved in this Paleozoic orogeny during the Early Silurian–Late Carboniferous. We infer that the Dunhuang orogenic belt is part of the Central Asian Orogenic Belt (CAOB), and thus the CAOB probably extends beyond the Beishan orogenic collage and southward into the Dunhuang region. [ABSTRACT FROM AUTHOR]

Subduction zones provide important constraints on reconstruction of tectonic configurations and convergent geodynamics. The timing and evolution of the subduction zones at the interaction between the Paleo‐Asian and Tethyan Oceans remain ambiguous, casting significant uncertainty on the reconstructions of proto‐Asia and subduction dynamics. Here, we report new petrologic and geochronologic data of a high‐grade metamorphic complex in the Dunhuang area, NW China, together with thermodynamic modeling, geothermobarometry, and second ion mass spectrometry U‐Pb chronology to reveal the complex metamorphic structure and history of the Paleozoic subduction‐exhumation channel at the intersection of the Paleo‐Asian and Tethyan domains. The subduction zone contains a diverse collection of eclogite, high‐pressure (HP) granulites, amphibolites, and metasedimentary rocks with a broad spectrum of P‐T‐t paths, which were buried and exhumed at different depths at ∼463–411 Ma. Our first dating of the oldest (∼463 Ma) HP granulite extends the orogenic period earlier to the Middle Ordovician. The uneven change in subduction gradients from ∼18°C/km to ∼10°C/km illustrates the thermal evolution of the subduction zone from infancy to maturity. A dramatic drop of the gradient at ∼420 Ma suggests a potential short‐term switch of the subduction dynamics from "hot" to "cool," possibly due to plate geometry reorganization in response to slab roll‐back. Our data demonstrate that the Dunhuang Complex was chaotically mixed and juxtaposed at different levels in the subduction‐exhumation channel. The southward younging and increase in depth of the HP metamorphism indicate that the Dunhuang Complex was formed by north‐dipping subduction of the Proto‐Tethyan Ocean from the Early Paleozoic. Plain Language Summary: The exhumed metamorphic complex in the Dunhuang area, NW China, provides primary evidence of how a deep subduction zone was constructed and evolved during the interaction between the Paleo‐Asian and Tethyan Oceans. Knowledge of these tectonic relations is essential to reconstruct the history of accretion of proto‐Asia. Our new petrologic and geochronologic data from the Dunhuang Complex reveal the metamorphic history of Paleozoic subduction‐exhumation. We report the oldest Ordovician (∼463 Ma) high‐pressure granulite and demonstrate that the regional thermal gradient during subduction ranged from ∼18°C/km to ∼10°C/km between ∼463 and ∼411 Ma. These results make the Dunhuang Complex one of the finest natural exposures on Earth that highlights how fast and how much a thermal gradient of subduction can evolve over time. Diverse P‐T‐t paths of these high‐grade metamorphic rocks indicate that the Dunhuang Complex was a Paleozoic accretionary forearc that was produced by km‐scale mixing and tectonic juxtaposition of diverse rocks in a subduction‐exhumation channel during closure of the Tethyan Ocean. Key Points: The T/P gradient of the Dunhuang Complex varied unevenly from ∼18°C/km to ∼10°C/km between the Middle Ordovician and Early DevonianA dramatic drop of the gradient at ∼420 Ma highlights a potential short‐term change in the subduction dynamics in response to slab roll‐backDiverse P‐T‐t paths indicate a Paleozoic accretionary forearc produced by km‐scale mixing and juxtaposition of rocks in a subduction channel [ABSTRACT FROM AUTHOR]

The Mashan Complex of the Jiamusi Massif was traditionally considered as the oldest stratigraphic sequence in eastern NE China. However, the metamorphic degree of the Mashan Complex is different in different areas, which can be divided into Jixi–Mishan–Hulin granulite facies belt and Luobei–Huanan–Mudanjiang amphibolite facies belt. Here, we investigated the Mashan Complex in the Yilan area and present lots of new petrological, mineral chemical, geochemical, and U–Pb geochronological data, in addition to phase equilibria modelling, to constrain the timing of metamorphism, P–T conditions, and the P–T path of the Mashan Complex, and furthermore to deduce the crustal evolution of the Jiamusi Massif. The protoliths of the Mashan Complex in the Yilan area are greywackes and felsic sandstones, whose provenance is dominantly felsic rocks formed from a continental island arc. Petrographic observations, traditional thermobarometry, and quantitative phase equilibria modelling of the studied samples reveal P–T conditions from M2 to M3 of ~7.2 kbar/760–800°C and 4.5–5.0 kbar/585–610°C, respectively, which together define a clockwise P–T path involving decompressional cooling (M3) that followed the peak granulite‐facies metamorphism (M2). It reveals essential information related to the collision orogeny and post‐collision process. Zircon U–Pb dating of two felsic rocks yielded the peak of the granulite‐facies metamorphism in the Yilan area of the Jiamusi Massif that might have occurred at ~500 Ma. The overall deposition of the metamorphic rocks was later than ~760 Ma and that most of the detrital materials came from late Mesoproterozoic and early Neoproterozoic source rocks. [ABSTRACT FROM AUTHOR]

Triassic magmatism in Northeast (NE) China was geodynamically controlled by the Mongol–Okhotsk Ocean (MOO), Palaeo-Asian Ocean (PAO), and Palaeo-Pacific Ocean (PPO) tectonic regimes. To define the mechanisms of crustal accretion and geodynamics, the magmatic processes generated by ocean closure and plate subduction must be determined. In the present study, we assembled geochronological, geochemical, Cu (Mo)-porphyry deposit, and zircon Hf isotopic data from magmatic rocks throughout NE China. Central-NE China harbours more reworking of juvenile continental crustal material than the NE China margin. The widespread Triassic felsic magmas in NE China are primarily due to the recycling of juvenile and ancient crustal components during the tectonic evolution of the PAO. During the Triassic, NE China was subjected to a syn- to post-collisional orogenic regime accompanied by scissor-like basin closure and bidirectional subduction of the eastern PAO, before transitioning to the PPO tectonic regime in the latest Triassic. Magmatism in the Erguna and the central–northern Xing'an blocks was more affected by the MOO tectonic regime. Magmatism in the central–southern Xing'an Block, the southwestern Songliao Basin, and northern Lesser Xing'an–Zhangguangcai Range was linked to the closure of the PAO. Triassic magmatic rocks along the eastern Songliao Basin are extensional and formed during the opening of the Mudanjiang Ocean. The NE margin of Eurasia was a passive continental margin in the Late Triassic. [ABSTRACT FROM AUTHOR]

The North Qilian Orogenic Belt is surrounded by the Tarim Craton to the NW and the North China Craton to the NE. The Precambrian continental crust remnants that are distributed in the North Qilian Orogenic Belt are termed the North Qilian Block (NQB), and their tectonic evolution has profound implications for the evolution of the Columbia Supercontinent. Here we present major- and trace-element and Sr–Nd–Hf isotope data for (meta-) basalts from the Beidahe Group (BDHG) and Zhulongguan Group (ZLGG) in the western North Qilian Orogenic Belt, to investigate the tectonic evolution of the NQB during the Proterozoic Eon. The protoliths of Palaeoproterozoic amphibole gneisses and plagioclase amphibolites from the BDHG are calc-alkaline series basalts. These metabasalts show island-arc-basalt affinities with variable Nd and Hf isotopes (ϵNd(t) = −5.0–0.6 and 2.7–4.3; ϵHf(t) = −14.2–2.0 and 6.9–8.8) and were generated by partial melting of the asthenospheric mantle that was metasomatized by aqueous fluid and sediment melt in a continental-arc setting. The early Mesoproterozoic ZLGG basalts show features of shoshonite-series basalts and are geochemically similar to ocean-island basalts. These basalts show variable (87Sr/86Sr)i, ϵNd(t) and ϵHf(t) values of 0.70464–0.70699, −1–2.6 and −1.5–5.7, and are products of mantle plume magmatism that participated with subducted oceanic crust in an intracontinental rift setting. This study suggests that the NQB underwent tectonic evolution from palaeo-oceanic subduction to intracontinental rifting during the Palaeoproterozoic–Mesoproterozoic eras. Furthermore, the above tectonomagmatic events were in response to convergence–splitting events of the Columbia Supercontinent during the Palaeoproterozoic–Mesoproterozoic eras. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogenic collages in the world with prominent juvenile crust addition, where the southernmost margin of the CAOB located is one hot topic in the international studies. The Dunhuang Block located to the south of the Beishan Orogen is a key position for outlining the tectonic framework of the south margin of the CAOB. However, at present, the tectonic attribution of the Dunhuang Block is still controversial. In this paper, we focus on the origins and protoliths of the meta‐mafic rocks from the Hongliuxia complex in the southern Dunhuang Block for determining the tectonic attribution of the Dunhuang Block. In the field, the meta‐mafic rocks are mainly exposed as tectonic blocks within the metasedimentary rocks displaying the "block‐in‐matrix" fabrics or as tectonic slices juxtaposed by faults. Geochemically, the meta‐mafic rocks could be divided into three groups based on the rare earth elements (REE) and trace elements: the group 1 samples are depleted in the LREE relative to HREE and show flat HREE patterns, similar to the mid‐oceanic ridge basalt; the group 2 samples show flat REE patterns without obvious differentiation between the LREE and HREE, like the oceanic plateau basalt; the group 3 samples are enriched in LREE relative to LREE, and have negative Nb, Ta, and Ti anomalies, similar to the island arc basalt. Conclusively, the protoliths of the meta‐mafic rocks dominantly belong to the oceanic plate components. They were metamorphosed during Early Silurian to Middle Devonian in different depths of the subduction zone documented in previous studies. So, we suggest the Hongliuxia complex is an exhumed Palaeozoic subduction–accretion complex (SAC) formed during the oceanic plate subduction. This result confirms the Palaeozoic subduction event occurred in the Dunhuang region and indicates that the Dunhuang Block is a Palaeozoic Orogen rather than a part of Precambrian continent block. Considering the regional geology context, we speculate the Dunhuang Orogen belongs to the southernmost margin of the CAOB. [ABSTRACT FROM AUTHOR]

The North Altyn Tagh ductile shear zone is well exposed in the Kaladawan area of North Altun orogenic belt. The deformed rocks provide clues to the deformation conditions and the tectonic evolution of the North Altun orogen. This study investigated structural deformation in Kaladawan of North Altun orogenic belt using magnetic fabric and electronic backscattered diffraction (EBSD) quartz fabric in order to reveal the dynamic and kinematic characteristics of the North Altyn Tagh ductile shear zone. We conducted detailed field investigations and collected oriented samples to analyse magnetic and EBSD fabrics. The mean magnetic susceptibility (Km) value for the Kaladawan rocks is low, indicating that paramagnetic and diamagnetic minerals are the principal carriers of magnetic susceptibility. The corrected degree of anisotropy (Pj), magnetic lineation (L), magnetic foliation (F), shape parameter (T), and oblateness of the magnetic susceptibility ellipsoid (E) show that the deformation in the central part of a transect across Kaladawan is weak indicating elongated prolate strain, whereas the deformation in the north and south is strong indicating oblate strain. The anisotropic magnetic susceptibility (AMS) principal ellipsoidal axis K1 (magnetic lineation) trends mainly WNW–ESE and are oriented with variable magnetic foliation attitudes, whereas the AMS principal axis K3 (pole to magnetic foliation) trends NNE–SSW. Deformation under different conditions generated two types of quartz c‐axis fabric style: type A (point maximum) and type B (Y maximum plus crossed girdles). Fabric thermometry analyses suggest that the quartz fabrics formed at a medium temperature of 400–500°C. According to previous zircon U–Pb data from Kaladawan, deformation of the North Altyn Tagh ductile shear zone took place between 478.1 and 427.3 Ma. The ductile shear can be interpreted as a tectonic response to dextral oblique convergence between the Tarim and Central Altun blocks. [ABSTRACT FROM AUTHOR]

The Fuping area lies in the middle part of the Trans‐North China Orogen, which is a critical region for understanding the metamorphic–tectonic evolution of this orogenic belt in the Precambrian. The newly discovered orthopyroxene‐bearing semipelitic granulite in this area is a coherent stratigraphic unit, among which three generations of metamorphic mineral assemblages (peak, post‐peak and cooling retrograde) have been identified based on petrographic observation and mineral chemical analysis. The peak metamorphic mineral assemblage mainly consists of porphyroblastic garnet plus matrix minerals including biotite, plagioclase, orthopyroxene, quartz as well as accessory minerals including pyrite, monazite, zircon and apatite. Geothermobarometry calculations and phase equilibria modelling confirm that the representative samples record different P–T conditions and metamorphic stages due to retrogressive metamorphism, with the highest P–T conditions reaching high‐P granulite facies. The retrieved clockwise metamorphic P–T paths pass from 12.5 to 13.5 kbar/855–880℃ (peak stage) through 8.5–11 kbar/850–886℃ (post‐peak stage) and to a speculative cooling phase (retrograde stage), reflecting near isothermal decompression (ITD) followed by near isobaric cooling (IBC). This P–T path is interpreted to reflect a subduction and/or collision event followed by a rapid exhumation. Secondary ion mass spectrometry (SIMS) U–Pb dating on metamorphic monazite and zircon yielded metamorphic ages ranging from 1,825 to 1,815 Ma, possibly constraining a retrograde metamorphic age. Therefore, the semipelitic granulite in the Fuping area records the subduction/collision event between the Eastern and Western Blocks of the North China Craton during the Late Palaeoproterozoic. [ABSTRACT FROM AUTHOR]

References 1 A. Aouizerat, W. Xiao, K. Schulmann, B.F. Windley, J. Zhou, J. Zhang, S. Ao, D. Song, P. Monie, K. Liu, Accretion, subduction erosion, and tectonic extrusion during late Paleozoic to Mesozoic orogenesis in NE China. 2020, 4 L. Feng, S. Lin, L. Li, D.W. Davis, C. Song, J. Li, S. Ren, X. Han, Y. Ge, K. Lu, Constraints on the tectonic evolution of the southern central Asian orogenic belt from early Permian-middle Triassic granitoids from the central Dunhuang orogenic belt, NW China. 2020, 10 H.T. Ma, X. Ma, J.F. Chen, B. Chen, C. Li, L.M. Zhou, H.Z. Yang, The Zhangjiatun igneous complex in the southeastern margin of the Central Asian Orogenic Belt, NE China: Evidence for an Early Paleozoic intra-oceanic arc. Shi, Q. Hou, C. Wu, Q. Yan, H.Y. Wang, N. Cheng, Q. Zhang, Z.M. Li, Paleozoic Sanweishan arc in the northern Dunhuang region, NW China: The Dunhuang block is a Phanerozoic orogen, not a Precambrian block. [Extracted from the article]

Comprehensive petrological, zircon U–Pb dating, whole‐rock geochemical, and Sr–Nd isotopic data are reported for the Duobagou volcanic rocks, intercalated with terrigenous clastic sequence, composing former Jurassic strata located at southeastern Dunhuang region, NW China. Duobagou volcanic interlayer is mainly composed of trachyandesite. LA–ICP–MS zircon dating yields a weighted mean 206Pb/238U age of 201.4 ± 3.4 Ma, affirming the formation of Late Triassic. The trachyandesites are characterized by enrichment of LREE relative to HREE with negative Eu, Sr, and Ti anomalies. The εNd(t) values (−0.24–1.91) and (87Sr/86Sr)i (0.7037–0.7049) shows an affinity of OIB. The Duobagou trachyandesite and Lucaogou basalt were proposed to be produced via 1–5% and 10–20% partial melting of the spinel–garnet‐bearing metasomatic enriched mantle and crystal fractionation coupled with slight extents of crustal contamination. Due to the delamination of thickened continental crust and asthenosphere upwelling, lower crustal material metasomatized and enriched the mantle source, leading to the eruption of trachyandesite. The Duobagou trachyandesite, Lucaogou sub‐alkaline basalt and thick sedimentary strata revealed that the Dunhuang region remained in an extension setting accompanied by rifting from Late Triassic to Middle Jurassic. [ABSTRACT FROM AUTHOR]

In this study, we document the kinematics and Late Quaternary slip rates of actively developing faults and folds on the northern side of the Altyn Tagh Fault (ATF) that accommodate uplift and lateral expansion of the northern Tibetan Plateau. Field observations and detailed measurements using Unmanned‐Aerial‐Vehicle Structure‐from‐Motion high‐resolution imagery of offset fan surfaces, gullies, and channel risers coupled with optically stimulated luminescence and 10Be ages constrain the timing and slip rates of the Sanweishan Fault (SWSF) and Nanjieshan Fault (NJSF) systems. The NE striking SWSF is characterized by sinistral strike slip with a top‐to‐the‐NW thrusting component. Offset geomorphic markers and dating results yield Pleistocene strike slip and vertical uplift rates of 0.06–1.25 mm/a and 0.05–0.08 mm/a, respectively. The E‐W trending NJSF is dominated by north and south directed thrusting and km‐scale folding with variable components of sinistral strike slip. The calculated total N‐S shortening rate across the NJSF is ~0.3 mm/a. Low rates of deformation for the SWSF and NJSF account for less than 10% of the total intraplate strain accommodated along the northeasternmost ATF system. Over a 1,000‐km length, the northward expansion of the Tibetan Plateau occurs by progressive northeastward growth of a transpressional duplex rooted SE into the ATF. An assumed crustal strength discontinuity along the northeast trending southern margin of the Tarim Craton focuses oblique convergence along the ATF. Oblique‐slip thrusting and sinistral strike slip along the ATF and to the north accommodate the oblique convergence, consistent with the ENE directed geodetically derived crustal velocity field driven by India's continued indentation 1,500 km to the south. Key Points: Kinematics and slip rates of the Sanweishan and Nanjieshan Fault systems directly north of the Altyn Tagh Fault (ATF) are newly constrainedThe north side of the ATF is a regionally evolving transpressional duplex accommodating Tibetan Plateau expansion into the Tarim CratonSlowly deforming faults of the Sanweishan and Nanjieshan may present an underappreciated seismic hazard for Silk Road Corridor cities [ABSTRACT FROM AUTHOR]

The petrology, geochemistry, zircon U–Pb geochronology, and Hf isotopes of Duobagou diorite and Karatashtage diorite were studied to establish the evolution of Palaeozoic orogeny in the Dunhuang area in Western China. The weighted mean 206Pb/238U age of 448 ± 2 Ma in zircon grains from Duobagou diorite indicated an origin in the late Ordovician Period; age‐corrected εHf(t) values of −0.98 to +4.46 correspond to a two‐stage zircon Hf model age (TDM2) of 1,145 Ma to 1,477 Ma. Karatashtage diorite has a weighted mean 206Pb/238U age of 436 ± 3 Ma, indicating an origin in the early Silurian Period; age‐corrected εHf(t) values of −1.13 to +7.96 correspond to a two‐stage zircon Hf model age (TDM2) of 718 Ma to 1,301 Ma. These findings indicate that Duobagou and Karatashtage diorites were derived from ancient crust. Duobagou diorite has high levels of Al2O3 (15.76%~17.64%), MgO (2.18%~5.44%), Mg# (40~51), Na2O (2.78%~4.19%), Sr (466~1,160 ppm), and Ba (523~892 ppm), low levels of K2O (1.29%~3.13%) and TiO2 (0.64%~1.0%), variable levels of Cr (73.4~253 ppm) and Ni (42.2~98.8 ppm), and depleted HREEs. Karatashtage diorite is characterized by high levels of Al2O3 (16.33%~17.59%), MgO (4.15%~7.10%), Mg# (50~59), Na2O (3.39%~4.41%), Cr (73.4~253 ppm), Ni (42.2~98.8 ppm), Sr (466~1,160 ppm), and Ba (523~892 ppm), low levels of K2O (1.29%~3.13%) and TiO2 (0.64%~1.0%), and depleted HREEs. The Duobagou pluton and the Karatashtage pluton display arc signatures, suggesting that they were formed by the partial melting of a subducted slab under garnet–amphibolite facies in an active continental margin, and an interaction between melt and mantle materials during emplacement. Subduction of the oceanic plate in the Dunhuang terrane occurred during the Early Silurian Period (435–430 Ma), which is close to that of the Beishan orogenesis but later than the formation of the Hongliugou–Lapeiquan ophiolitic belt. We suggest that the Dunhuang terrane underwent an orogenic process related to the Palaeo‐Asian Ocean during the Early Palaeozoic Era, and that it belongs to the Central Asian Orogenic Belt (CAOB). [ABSTRACT FROM AUTHOR]