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Subduction infancy corresponds to the first few million years of the start of subduction following heat transfer from the incipient mantle wedge towards the slab‐top, as witnessed by metamorphic soles which represent slivers of oceanic crust metamorphosed up to granulite facies conditions welded beneath obducted ophiolites. In this study, integrated petrological, geochemical, mineralogical, geochronological, and thermodynamic studies were carried out on samples from the Yushugou high‐temperature metamorphic ophiolitic complex (YHTM) in the South Tianshan Accretionary Complex (STAC), where a massive exposure of coherent granulite accompanied by a thick peridotite body is preserved. Bulk‐rock compositions and Sr–Nd–Hf isotopes demonstrate the petrogenesis of meta‐basalts with oceanic island basalt (OIB)‐like and mid‐ocean ridge basalt (MORB)‐like affinities, with little infiltration by subduction‐derived melts and/or fluids (e.g., no negative Nb–Ta anomalies). Thermodynamic modelling and U–Pb chronology reveal that the YHTM meta‐basalts experienced granulite facies metamorphism of ~840–940°C and ~0.92–1.02 GPa at c. 392 Ma and then possibly reheating and zircon alteration in the Carboniferous. In addition, detrital zircons in sedimentary host rocks of the YHTM show limited Precambrian records and offer maximum depositional ages of c. 410–400 Ma together with the oldest Palaeozoic cluster around c. 470–450 Ma. It is suggested that the YHTM granulites could be of Ordovician–Silurian protolith and such an age pattern significantly deviates from those of adjacent terranes (the Central Tianshan, STAC, and North Tarim Craton). Combined with the compilation of pressure–temperature–time estimates of the YHTM and ages of regional ophiolites, arc intermediate‐mafic rocks, A‐type granites, and deformation, a model of induced, temporarily northward, intra‐oceanic subduction initiation is proposed, which probably occurred along the previously existing weak zone close to a seamount or oceanic plateau in the earliest middle Devonian during the northward subduction of the South Tianshan Ocean (STO). Anomalously high geothermal gradients could be triggered by asthenosphere upwellings, further facilitating the formation of OIB‐type metamorphic soles. The YHTM, which represents the remnant of metamorphic soles and associated ophiolites, was finally emplaced to the north margin of the STAC during the relatively long‐term (c. 160 million years) accretion and continuous subduction of the STO before its closure. This finding also presents a new natural example of OIB‐type metamorphic soles as a snapshot of fossil intra‐oceanic subduction infancy during the complex evolutionary history of the STO. [ABSTRACT FROM AUTHOR]

Late Palaeozoic evolution of the Chinese Altai-East Junggar orogenic collage is vital for a better understanding of the accretionary evolution in the southern Altaids. This paper reports new geochronological, geochemical, and isotopic data for the magmatic rocks collected from the northern part of the Dulate arc. The ~304.6 Ma tonalite samples present typical adakitic features of high Sr (396–714 ppm), low Y (1.42–2.60 ppm), Yb (0.11–0.24 ppm), and high Sr/Y (177.25–440.23) ratios. Combining high Mg# (55.35–57.21) and depleted isotopic composition (εHf(t): +9.89 to +13.37 and εNd(t): +5.36 to +6.06), we suggest that they were derived from the partial melting of a subducted oceanic slab. The ~299.4 Ma monzogranite samples have high A/CNK values (1.08 to 1.25), CIPW normative corundum contents (1.28–3.25 wt.%), and positive εHf(t) (+5.14 to +8.63) and εNd(t) (+1.08) values, which are similar to S-type granite that may be generated by the melting of greywackes. The monzogranite (~286.9 Ma) and rhyolitic porphyry (~283.9 Ma) are high-K calc-alkaline and similar to the highly fractionated I-type granites with depleted isotopic features (εHf(t): +11.68 to +14.99 and +0.75 to +7.18, εNd(t): +5.91 and +6.18). The monzogranite and rhyolitic porphyry could have been derived from a depleted mantle source, but the rhyolitic porphyry probably suffered partial assimilation of the overlying crust materials. Combining regional rock associations of mafic-ultramafic complexes, adakitic rocks, high-Mg diorites, and A-type granites with close spatial-temporal relationship, we conclude that a mid-oceanic ridge of the Ob-Zaisan Ocean subducted southward beneath the Dulate arc during the latest Carboniferous to Permian. With the opening of the slab window, the upwelling asthenosphere provided high heat flux and triggered various magmatism in the upper plate. We propose that ridge subduction is one of the most effective mechanisms of continental growth in the southern Altaids. [ABSTRACT FROM AUTHOR]

Identification and anatomy of oceanic arcs within ancient orogenic belt are significant for better understanding the tectonic framework and closure process of paleo‐ocean basin. This article summarizes the geological, geochemical, and geochronological characteristics of upper crust of Proto‐Tethyan Lajishan intra‐oceanic arc and provides new data to constrain the subduction evolution of the South Qilian Ocean. The intra‐oceanic arc volcanic rocks, including intermediate–mafic lava, breccia, tuff, and minor felsic rocks, are distributed along southern part of the Lajishan ophiolite belt. Geochemical and isotopic compositions indicate that the intermediate–mafic lava were originated from depleted mantle contaminated by sediment melts or hydrous fluids, whereas the felsic rocks were likely generated by partial melting of juvenile mafic crust in intra‐oceanic arc setting. Zircons from felsic rocks yield consistent and concordant ages ranging from 506 to 523 Ma, suggesting these volcanic rocks represent the relicts of upper crust of the Cambrian intra‐oceanic arc. Combined with the Cambrian forearc ophiolite and accretionary complex, we suggest that the Cambrian intra‐oceanic arc in the Lajishan ophiolite belt is belonging to the intra‐oceanic arc system which was generated by south‐directed subduction in the South Qilian Ocean at a relatively short interval between approximately 530 and 480 Ma. [ABSTRACT FROM AUTHOR]

A dominantly NW-SE directed extensional tectonics in the Early Cretaceous significantly reworked the Late Permian-Triassic orogenic framework of the Dabie orogenic belt. The North Dabie complex (NDC) is the principal domain recording this tectonic event. However, the precise structure-kinematic architectures, particularly those observed in the ductile regime, along with the respective time scales for different extensional stages, have not been adequately established. This significantly impedes our comprehensive understanding of the extensional style and deformation history in the North Dabie complex. To better address these issues, we conducted a systematic structural study and LA-ICP-MS zircon U-Pb dating of the pre-, syn-, and post-kinematic intrusions and syn-kinematically metamorphosed high-grade gneisses/migmatites of the NDC. Our results demonstrate that the extensional deformation in the NDC may initiate at ca. 144 Ma, which is characterized by a pervasive NW-SE oriented coaxial plastic flow in the ductile regime of the middle-lower crust. A large-scale detachment processing zone subsequently started activating at ca. 140 Ma at the upper-middle level of the middle crust, and concentratedly accommodated the extensional strain by top-to-NW ductile shearing. Locally, there was uprising of sub-magmatic flow in the atatexite-diatexite from the deeper lower crust taking place in the manner of top-to-outward shearing as early as ca. 137 Ma. This composite process of extension manifests vertical strain partitioning across the ductile middle-lower crusts and progressive strain localization during the lithospheric thinning. The NW-SE orientation dominated extensional tectonics was strongly driven by the westward subduction of the Paleo-Pacific oceanic plate during the Late Mesozoic. [ABSTRACT FROM AUTHOR]

Continental‐scale shear zones in Indochina record Cenozoic tectonic processes in SE Asia. Previous extrusion models link these shear zones to northward indentation of the Indian continent and conflict with distributed Oligocene conjugate strike‐slip pairs, formed by E‐W‐directed compression (present coordinates). This paper presents evidence of Oligocene shearing along the Mogok Metamorphic Belt in Myanmar, the western boundary of the Indochina block. The Kyanigan quarry at northern Mogok Metamorphic Belt exposes paragneiss, marble and quartzite schist with E‐W striking, which would be dragged from N‐S striking foliations of the main Mogok Metamorphic Belt by right‐lateral shearing of the brittle Sagaing Fault. After restoration, right‐lateral shearing 'σ' structures, cored with garnet, in paragneiss in the Kyanigan quarry are consistent with 'σ' and 'δ' structures in the Moulmein granitic mylonite to the south. U–Pb ages of metamorphic zircon of a sheared paragneiss and a leucogranite, cross‐cutting shear foliation in the Kyanigan quarry, and a biotite 39Ar‐40Ar age of mylonite at Moulmein constrain dextral shearing to 33–25.4 Ma, coeval with other 31–24.5 Ma shear zones in Indochina. The eleven NW‐striking left‐lateral shear zones and N‐S to NE‐striking right‐lateral shear zones define Oligocene conjugate fault patterns in Indochina. After restoration of ~80–45° clockwise rotation, these Oligocene conjugate shear zones, coupled with the anticlinal configuration of the Xuelongshan and Doi Inthanon‐Doi Suthep domes, reflect approximate N–S‐directed shortening. These structures to the north with coeval Myanmar‐Sumatra magmatic arc to the south demonstrate that they correspond to back‐arc contraction during northward subduction of the Indian Ocean. Oligocene continental‐scale intra‐continental shearing may be triggered by syn‐subduction compression in SE Asia. [ABSTRACT FROM AUTHOR]

The possibility that the Proto‐Tethys Ocean may have undergone intra‐oceanic subduction during ocean closure remains poorly constrained due to a lack of geological evidence for a mature intra‐oceanic arc. Here we present new geochemical and geochronological data for potential arc‐related volcanic rocks adjacent to the accretionary complex and forearc basin in the North Qaidam collisional belt, northern Tibetan Plateau. The volcanic rocks are dominated by foliated basalt, andesite, tuff, and minor dacite with zircon U‐Pb ages ranging from 517 to 497 Ma. They show distinctive geochemical characteristics and can be subdivided into three groups: island‐arc intermediate‐basic volcanic rocks, back‐arc basin basalts (BABB), and dacites with intra‐oceanic arc affinity. The island‐arc volcanic rocks have variable εNd(t) values (+1.6 to +7.5) that decrease northward and were generated by partial melting of depleted mantle wedge modified by hydrous fluid and sediment melt. The BABBs have high εNd(t) values (+5.3 to +6.6) and formed through the melting of MORB‐like mantle, whereas the nearby dacites have positive εNd(t) values (+1.9 to +3.6) similar to the surrounding island‐arc volcanic rocks and were derived from partial melting of intra‐oceanic arc crust as a result of BABB underplating. Integrated analysis of the spatial‐temporal distribution of these volcanic rocks and the reconstructed intra‐oceanic arc‐trench system confirms the existence of the earliest Phanerozoic intra‐oceanic arc formed in response to north‐directed intra‐oceanic subduction. This unrecognized subduction of the Proto‐Tethys Ocean in the North Qaidam belt initiated at ca. 530 Ma, matured ca. 520 Ma, and terminated by ca. 480 Ma. Plain Language Summary: Closure of an ocean basin is achieved through subduction of oceanic lithosphere at a continental margin or in an intra‐oceanic setting. Identification and structure of subduction‐related magmatic rocks are critical for fully understanding the complex processes associated with ocean closure and the paleotectonic framework. Geological mapping and geochemical analyses of the Tanjianshan Group in the North Qaidam collisional belt, northern Tibetan Plateau were undertaken. Results demonstrate the presence of relics of the earliest Phanerozoic intra‐oceanic arc and an associated complete arc‐trench system, generated by previously unrecognized intra‐oceanic subduction far from microcontinents that are now adjacent. This study reveals the entire evolution of a missing intra‐oceanic subduction system within the Proto‐Tethys Ocean, which started ca. 530 Ma, matured ca. 520 Ma and ended ca. 480 Ma. Key Points: Relics of the earliest Phanerozoic intra‐oceanic arc discovered in North Qaidam collisional beltProto‐Tethys Ocean in North Qaidam belt experienced north‐directed intra‐oceanic subductionIntra‐oceanic subduction started at ca. 530 Ma and lasted until ca. 480 Ma [ABSTRACT FROM AUTHOR]

Mantle heterogeneity has revealed systematic differences in Pb isotopic compositions between the Indian Ocean-South Atlantic mantle in the Southern Hemisphere and the Pacific Ocean-North Atlantic mantle in the Northern Hemisphere. This large-scale difference in mantle isotopes in the Southern Hemisphere is known as the DUPAL anomaly, but its origin remains controversial. Based on a systematic review of the Nd-Pb isotopic evolution of the Tethyan mantle domain, this study identified the long-term presence of the DUPAL anomaly in this domain since the early Paleozoic, characterized by long-term and high mantle thorium/uranium (Th/U) ratios. By comparing the Nd-Pb isotopic compositions of the Tethyan mantle domain with the Panthalassic-Pacific mantle domain (the Paleo-Asian, Paleo-Pacific, and modern Pacific oceans), it is shown that the mantle initially had low Th/U features due to early Earth crust-mantle differentiation, with the crust having high Th/U ratios. As such, the mantle initially had uniformly low Th/U ratios that were inherited throughout the Panthalassic-Pacific mantle domain. However, the plate tectonics and continental collisions in the Tethyan domain affected its characteristics, leading to the long-term and large-scale DUPAL anomaly. During the opening of and subduction in the Tethys Ocean, Gondwanaland fragmentation and frequent continent-continent collisions led to long-term and extensive crust-mantle interactions and the continuous input of high-Th/U mantle sources, which thus modified the mantle. This process formed not only the unique DUPAL anomaly in the Tethyan mantle domain, but also the Tethyan tectonic domain dominated by continental collisions. Moreover, the high DUPAL anomaly in the Proto- and Paleo-Tethyan mantle domains records the effects of mantle plumes, which might have occurred primarily during the formation of the Proto- and Paleo-Tethys oceans during the early evolution of the Tethyan domain. Therefore, the inherent coupling of mantle domain properties and plate tectonic mechanisms provides important insights for understanding plate tectonics and geodynamic processes in the Tethyan domain. [ABSTRACT FROM AUTHOR]

The late Early Permian basaltic rocks in the West Junggar of northwest China provide a critical geological record for revealing the termination of the Late Palaeozoic final-stage subduction history of the southwestern Palaeo-Asian Ocean. With the aim of providing constraints on the late stage of the Late Palaeozoic geodynamic evolution of the southwestern Altaids, an integrated study of detailed field observation, geochronology and geochemistry has been carried out on the Early Permian basaltic rocks from the Hala'alate Mountain of the southern West Junggar. Zircon LA-ICP-MS U-Pb dating of four basaltic andesites suggests that they were erupted during the late Early Permian with ages of ca. 286–283 Ma, coeval with the neighbouring mafic diabase stock and gabbroic dyke swarms. The basaltic rocks have low SiO2 and moderate MgO contents, with low (87Sr/86Sr)i ratios (0.70397–0.70447) and high positive εNd(t) values (+5.94–+7.19), and also show remarkable enrichment in large ion lithophile elements (Ba, U, K, Pb, Sr) and prominent depletion in high field strength elements (Nb, Ta, Zr, Hf, Ti), indicating that they were originated from the partial melting of a garnet-dominant with minor spinel lherzolitic depleted mantle source previously metasomatized by slab-derived fluids and subducted sediments. These basaltic rocks were most likely formed in a fore-arc extensional setting in response to the slab retreat of the Junggar oceanic slab during the mid-late stage of Early Permian. Combined with previously published regional achievements, our new results support that the down-going of the remnant oceanic slab and the resultant arc magmatic activity of the southern West Junggar probably continued until the ca. 283 Ma, and the closure of the West Junggar branch of the Palaeo-Asian Ocean should be later than the late Early Permian. [ABSTRACT FROM AUTHOR]

The evolution and closure timing of the Paleo-Asian Ocean are controversial in the Eastern Tianshan orogen, southern Altaids. The Dananhu arc of the Eastern Tianshan was involved in the long-lived evolution and terminal tectonic events during the formation of the Altaids, and its magmatic rocks are the faithful recorder. To constrain the subduction history of the Paleo-Asian Ocean, we review the tectonic of the Dananhu arc, by summarizing the geochemical and geochronological data of granites and volcanic rocks and mineral deposits, which will shed light on the accretionary history, closure of the Paleo-Asian Ocean, and the continental growth in Altaids. Zircon U-Pb ages of the granitic rocks across the middle of the Dannanhu arc range from 453 Ma to 227 Ma and demonstrate overall southward younging through four main areas: the Kalatage belt (ca. 453–299 Ma), the Keizer belt (ca. 401–268 Ma), the Tuwu belt (360–302 Ma), and the Kanguer subduction complex (ca. 288–227 Ma). These granitic rocks are calc-alkaline arc-related and adakitic granites that are enriched in Si and K. They increase in Th/Yb and decrease in Cr and Ce/Pb southwards over time. The consistent geochemical variations indicate progressive maturity of the arc crust. Their whole-rock εNd(t) and zircon εHf(t) values coordinated with the progressive change in the crustal thickness estimated by the granites indicate a multi-phase switching of subduction. The Ordovician to Permian granitic rocks in the arc have stable high whole-rock εNd(t) values (ca. +5 – +10), and zircon εHf(t) values (ca. +7-+16), which significantly shifted to +2 – +4 and +4 – +12 during ca. 243–227 Ma. These changing relations accompanied a sudden crustal thickening, suggesting that continental crustal material was involved in the petrogenesis of these rocks during the convergence among the Dananhu arc, the Harlik and the Yamansu-central Tianshan continental arc. [ABSTRACT FROM AUTHOR]

The Central Qilian terrane (CQT) of the northern Tibetan Plateau played a key role in the tectonic evolution of the Proto‐Tethyan Ocean in the Tethysides, but its formation and tectonic attribution have been hotly debated. Here, we report the discovery of eclogites and HP mafic granulites in the Beidahe Complex of the western CQT. These occur as blocks of various sizes within a sequence of metavolcanic–sedimentary rocks, exhibiting typical a 'block‐in‐matrix' and thrust imbrication structure. The eclogite facies metamorphic rocks preserve distinct mineral assemblages and textures corresponding to prograde, peak, and retrograde metamorphism. By combining phase equilibrium modelling with SHRIMP and LA‐ICPMS U–Pb dating of metamorphic zircon, sphene, and rutile, the Late Neoproterozoic–Cambrian (c. 553–516 Ma) eclogite facies peak with low thermal gradients of 10–14°C/km, Cambrian (c. 515–506 Ma) post‐peak decompression and Ordovician (c. 495–455 Ma) cooling histories for these metabasic rocks have been restored. These constitute hairpin‐type clockwise pressure–temperature–time (P–T–t) paths depicting in detail the sequence of deep subduction and subsequent exhumation in Central Qilian during the Late Neoproterozoic to Early Palaeozoic. Our new findings suggest that the CQT represents a Japan‐type arc‐accretionary system that formed as a result of the North Qilian oceanic plate, one of the major branches of the Proto‐Tethys Ocean, being subducted southward. Eclogites in the Beidahe Complex in western CQT offer the earliest (c. 553 Ma) metamorphic record of subduction in the Qilian orogen, indicating that the North Qilian Ocean commenced subducting southward prior to the Late Neoproterozoic. [ABSTRACT FROM AUTHOR]

The subduction initiation and the early‐stage tectonics of the southern Paleo‐Asian Ocean have rarely been discussed. To address these problems, we report new geochemical and geochronological data of arc‐related volcanic rocks in the Huaniushan arc of the southern Beishan. Basaltic andesites and high‐Mg rocks yield zircon U‐Pb ages of 449–422 Ma and 460–437 Ma, respectively. The basaltic andesite is a continental arc‐related tholeiite with moderate amounts of TiO2; and is enriched in light rare earth elements (LREE), such as Rb, Ba, Th and Sr; it is also depleted in Nb, Ta and Eu; and has moderate εHf (t) (−0.3 to +5.5) and εNd (t) (−3.48 to +0.03) values; and high (87Sr/86Sr)i (0.7066–0.7079) values. The high‐Mg andesite and dacite are sanukitic‐type high‐Mg rocks, which have high MgO (Mg# = 49–62) contents, A/CNK (0.82–2.36) and (La/Sm)N values, low Sr/Y (3–15) and Ba/Th (11–182) ratios, moderate to low εHf (t) (−16.7 to +7.6) and εNd (t) (−3.74 to +0.05), and high (87Sr/86Sr)i values. All geochemical data indicate that they were sourced from mixing between mantle‐peridotite‐derived melts and silicic melts generated by the subducting oceanic slab and/or sediments in a hot subduction setting. After integrating the Sanukitic high‐Mg andesites (HMAs) with previously reported Nb‐enriched basalt, volumes of arc‐related tholeiitic to calc‐alkaline volcanic rocks, I‐ to S‐type granites, and HT eclogites, we conclude that the subduction initiation was one of the most likely geodynamic process for the metamorphism and magmatism in the Middle Ordovician to early Silurian. Key Points: The Huaniushan high‐Mg rocks (460–437 Ma) are Sanukitic type high magnesium andesites (HMAs)The magmatic assemblages suggest a hot subduction in Middle Ordovician to early Silurian in the southern Beishan of the southern AlaidsMiddle Ordovician subduction initiation resulted volumes of Sanukitic HMAs, Nb‐enriched basalt, HT eclogite, and arc‐related magmatism [ABSTRACT FROM AUTHOR]

The Tien Shan orogenic belt is located in the western region of central Asia, which has been previously considered to have formed in the Paleozoic and reactivated in the Cenozoic. However, the dynamic processes and deep detailed structure of the Tien Shan orogen remain elusive. Seismic studies are expected to provide profound clues on the deep structure and dynamic mechanism of the mountain-building process. Regional Pn traveltime tomography provides opportunities for constructing a more detailed P-wave velocity model of the uppermost mantle linking the shallow crust and the upper mantle. In this work, a 3-D P-wave high-resolution velocity model in the uppermost mantle of the western and central Tien Shan is constructed by inverting the 20,940 Pn arrival time of the 1108 local and regional earthquakes retrieved from the ISC-EHB catalog. The 3-D fast-marching tomography (FMTOMO) package is used to invert the 3-D uppermost mantle velocity model with a resolution of 1° × 1°. We clearly observe descending high-velocity anomalies, extending from the lower crust down to 85 km, suggesting double subduction of the Kazakh lithosphere in the north and Tarim lithosphere in the south beneath central Tien Shan. Furthermore, a prominent low-velocity feature in the upper mantle of central Tien Shan might result from asthenospheric upwelling. The high-velocity anomaly in the upper mantle of the western Tien Shan may suggest the southward subduction of the Kazakh plate to the western Tien Shan and Fergana basins. A significant low-velocity anomaly in the uppermost mantle beneath the southwestern Tarim Basin might result from plume intrusion with evidence of mantle xenolith or plume-lithosphere interaction and its consequent upwelling. [ABSTRACT FROM AUTHOR]

The early Paleozoic accretionary architecture of the Alxa and Bainaimiao regions in southern Central Asian Orogenic Belt (CAOB) is still ambiguous. In particular, the subduction polarity and tectonic origin of the Bainaimiao Arc are intensely controversial. The Ganqimaodu area in Inner Mongolia provides an excellent window to address this issue. This study presents field and detrital zircon U–Pb–Hf isotopic data of Paleozoic (meta)sedimentary rocks from Ganqimaodu to investigate their provenance and tectonic settings. New field observations show that both the Ondor sum and Hadahushu groups are composed of slightly metamorphosed flysch deposits with pervasive occurrence of "block-in-matrix" structure and isoclinal folds. Two chlorite–quartz schists from the Ondor sum Group yield age peaks at ~ 425, ~ 966, ~ 1590, ~ 1930 and ~ 2564 Ma, and three sandstones from the Hadahushu Group display similar age spectrums with peaks at ~ 443, ~ 586, ~ 960, ~ 1473, ~ 1765 and ~ 2480 Ma. New detrital zircon ages constrain the maximum depositional ages of the Ondor sum and Hadahushu groups to Early Devonian. The Ondor sum and Hadahushu groups are here interpreted as an accretionary complex due to northward subduction of the South Bainaimiao Ocean based on field data and provenance analyses. Our new results combined with previous data suggest bidirectional subduction for the western segment of the South Bainaimiao Ocean during Late Cambrian to Early Devonian. We advocate an archipelago with accretionary complexes, continental fragments, and magmatic arcs for the architecture of the southern CAOB during early Paleozoic, an analogous to modern southwest Pacific accretionary system. [ABSTRACT FROM AUTHOR]

This study provides new constraints on the mantle transition zone (MTZ) structure under the Tian Shan orogenic belt in the context of the double‐sided subduction of the Junggar lithosphere and the Tarim lithosphere. The 410‐ and 660‐km discontinuities bordering the MTZ under the Tian Shan and its adjacent areas are mapped by stacking 68,361 receiver functions from 4,122 events recorded by 100 broadband seismic stations. Regional and large‐scale 3‐D velocity models are used to explain the effect of the laterally heterogeneous velocity anomalies. We identify a thickened MTZ of about 9.3 km under the eastern Tian Shan and the Darbut belt. This thickening indicates a lower temperature, which is correlated with the broken‐off subducted lithosphere or the delamination of the eastern Tian Shan lithosphere. We document the thinning of the MTZ caused by the depressed 410‐km discontinuity and the uplifted 660‐km discontinuity across the Tian Shan orogenic belt, Junggar Basin and Tarim Basin. This thinning corresponds to a + 100 K thermal anomaly in the MTZ, and we suggest that it may have been produced by thermal upwelling originating from the lower mantle. The slightly thinned MTZ beneath the Altai Mountains was caused by the uplift of these two discontinuities, which is related to the high‐velocity anomalies in the upper mantle and MTZ. In contrast, the thinned MTZ below the easternmost segment of the Tian Shan orogenic belt, formed by the depression of 6.5 km for the 410‐km discontinuity may indicate the presence of small‐scale mantle upwelling. Plain Language Summary: The tectonic activity of the Tian Shan orogenic belt is affected by the bidirectional subduction of the Junggar and Tarim lithosphere. However, the deep dynamic processes of the eastern Tian Shan has long been poorly constrained by independent seismological evidence. Based on the seismic data collected by 100 broadband seismic stations, the high‐resolution results of mantle transition zone (MTZ) structure were mapped using P‐wave receiver functions. The results reveal a thick MTZ under the eastern Tian Shan and Darbut belt caused by the uplifted 410 discontinuity, which may be related to delaminated lithosphere root or broken‐off lithosphere. The depressed 410‐km and uplifted 660‐km discontinuities across Tian Shan, Junggar Basin and Tarim Basin may originate from the thermal upwelling of the lower mantle. Our results provide valuable insight into the dynamic processes of plate subduction and mantle convection under the eastern Tian Shan orogenic belt. Key Points: The 410‐ and 660‐km discontinuities under the eastern Tian Shan were mapped using receiver functions with high resolutionThe thickening of mantle transition zone (MTZ) under Tian Shan and Darbut belt is associated with delaminated lithosphere root or broken‐off lithosphereThe thinning of MTZ across Tian Shan, Junggar Basin and Tarim Basin may originate from the thermal upwelling of the lower mantle [ABSTRACT FROM AUTHOR]

The enhanced preservation potential of continental material during continental convergence is thought to be responsible for the episodic continental growth process. However, the mechanism of preservation potential variation is unclear. In this study, we use a novel high‐density passive‐source seismic approach to image the whole‐crust architecture of the juvenile continent in southern Altaids. Two arcuate crust fragments are found between Paleozoic island‐arc belts, which indicate the relicts of inter‐arc oceanic basins. The results show that the trapped oceanic basins make up a large proportion of the juvenile continental crust and that the reduction in subduction erosion due to its incomplete subduction can explain a period of rapid continental growth revealed by previous zircon studies. We suggest that a large number of ocean basins may be trapped during supercontinent formation, and they play a critical role in continental material preservation and continental episodic growth. Plain Language Summary: The growth of the continental crust is an episodic process associated with the supercontinental circle, but a specific mechanism to explain it is still lacking. Here, we combined the seismic images with magnetic and geological data to reveal that two trapped oceanic basins form parts of the lower crust in southern Altaids. These oceanic basins are trapped in the gaps between continents and arcs because their boundaries are rarely having a jigsaw puzzle‐like fit. During this process, the continental crust grows significantly due to the addition of oceanic basins and the associated decrease in subduction erosion. We proposed that numerous oceanic basins could be captured during the formation of supercontinents, leading to peaks in continental crust growth. Key Points: We present a new high‐resolution image of the crustal structures of the Eastern Junggar using the receiver function methodCombing geomagnetic and geological data to identify trapped oceanic basins and reconstruct their trapping processInvestigating the contribution of trapped ocean basins to continental growth and the implications for global continental episodic growth [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 buckling orocline is generally formed by buckling of an originally straight or nearly straight orogenic belt, which formed in the first stage and was buckled in the second stage either by mountain-parallel/oblique compression (e.g. Cantabrian orocline [[12]]) or by mountain-perpendicular/oblique indentation (e.g. Adriatic Orocline [[13]], Peruvian and Bolivian oroclines [[3]]). Therefore, the orocline structure plays a key role in the development of accretionary orogen architecture and contributes to the formation of a huge orogenic belt, such as the CAOB. The term "orocline" was first proposed by Carey [[1]] to describe the structure as 'an orogenic system which has been flexed in plane to a horse-shoe or elbow shape'; it usually emphasizes that a previous straight mountain belt or tectonic units have been bended horizontally. [Extracted from the article]

Previous studies concluded that a Trans‐Tethyan oceanic subduction zone existed prior to Paleogene India‐Eurasia collision, when the ocean lacked intervening continental slivers. In this paper, we present the first report of Early Cretaceous shortening and 152.8 Ma alkali magmatism in the continental sliver Longzi block, a ca. 750 km E‐W by ca. 130 km N‐S tract of the NE Himalaya within the Himalaya orogen. The Longzi block contains overturned south‐vergent folds in Triassic‐Lower Cretaceous strata intruded by 136–123 Ma mafic‐dioritic‐dacite dikes, which constrain the time of Early Cretaceous shortening. Triassic strata with NW Australian affinity and Late Jurassic conglomerates derived from northern India record the pre‐rift history. Evidence for the rifting includes 152.8–145 Ma alkali intrusive rocks, a Late Jurassic unconformity, rapid changes in sediment thickness, and the water depth during deposition of Upper Jurassic strata. The rifting event was coeval with the formation of 152–155 Ma oceanic crust in the NE Indian Ocean and of a Late Jurassic submarine escarpment with 1,200 m of sediments offshore of NW Australia. These data show that the Longzi block was part of westernmost Argoland, a continental sliver that rifted from East Gondwana. The Longzi block subsequently collided with a N‐dipping Trans‐Tethyan intra‐oceanic subduction zone in the Early Cretaceous to generate the relevant shortening, long before the Paleocene continent‐continent collision along the Yarlung‐Tsangpo suture zone. This rift‐collision in the Himalayan region reflects the Mesozoic archipelagic paleogeography in eastern Neotethys, which was preceded by ocean closure, and the two‐stage collision of India‐Eurasia in the Cenozoic. Plain Language Summary: This study presents the first report of Early Cretaceous shortening and 152.8 Ma alkali magmatism in the Longzi block, a continental sliver between India and Eurasia in the NE Himalaya. Folds in Triassic‐Lower Cretaceous strata were intruded by 136–123 Ma dikes, suggesting Early Cretaceous shortening. This shortening counters the currently accepted model that the NE Himalaya experienced only an extension in the northern Indian passive margin at that time. In Mt. Kala (Chinese Tibet), 152.8 Ma alkali intrusive rocks are coeval with an unconformity, rapid changes in sediment thickness and depositional water depth in the Himalayan rocks, and with 152–155 Ma oceanic crust in the NE Indian Ocean. These relations demonstrate that the NE Himalaya contains evidence of Late Jurassic rifting. The Longzi block contains NW Australian‐affinity Triassic strata and Indian‐affinity Late Jurassic conglomerates, indicating derivation from East Gondwana before the rifting. These data show that the Longzi block was part of westernmost Argoland that separated from East Gondwana. This continental block had an archipelagic configuration between India and Eurasia in Neotethys that began in the Late Jurassic. Recognition of the Longzi continental sliver improves our understanding of the Mesozoic geodynamics of Neotethys, and confirms the two‐stage India‐Eurasia collision in the Cenozoic. Key Points: The Longzi block in the NE Himalaya records Early Cretaceous shortening and Late Jurassic alkali magmatismFirst geological evidence demonstrates that the Longzi block is the westernmost fragment of Argoland that was separated from East GondwanaNew archipelagic framework since the Late Jurassic demonstrates Mesozoic geodynamics of Neotethys and Cenozoic two‐stage collision in Tibet [ABSTRACT FROM AUTHOR]

The Altaids accreted around, and grew southward, from the Siberian craton, but the time of final amalgamation of this orogen is still controversial. The Eastern Tianshan in the southernmost Altaids is characterized by multiple, late, accreted arcs and thus is an ideal tectonic environment to answer the time of final amalgamation of the Altaids. In this study we report the results of new field-based lithological mapping and structural analysis on the Kanguer mélange in the Eastern Tianshan, which is composed of blocks of basalt, chert, limestone, and other rocks within a strongly deformed and cleaved matrix of sandstone and schist. Our geochemical and isotopic data of basaltic blocks from several parts of the Kanguer mélange show they are relics of Normal-Mid-Ocean-Ridge (N-MORB)-type oceanic lithosphere, and U–Pb ages and Hf isotopes of detrital zircons from the matrix sandstones indicate they were derived only from the Dananhu arc to the north. Accordingly, our interpretation is that the Kanguer mélange was part of an accretionary complex that fringed the Dananhu arc, and therefore the subduction polarity of the Kanguer Ocean was to the north (present coordinates). The maximum depositional ages (MDAs) of our three sandstone samples (08K01, 08K02, and 08K03) from the mélange matrix were 234 ± 14 Ma, 242.5 ± 1.3 Ma, and 236 ± 2.0 Ma respectively, indicating that the Kanguer Ocean was still being subducted at ca. 234 Ma, and the accretion of the Kanguer mélange must have lasted until that time, when the accretionary complex was still located opposite to the Yamansu-CTS accretionary complex to the south. Thus, the final amalgamation of the Dananhu and Yanmansu-CTS arcs took place by the welding of two accretionary complexes in the late Middle Triassic (Ladinian) in this part of the southern Altaids. Integration with relevant amalgamation histories throughout the Tianshan indicates that the time of terminal amalgamation in the southern Altaids was probably in the Middle-Late Triassic, which is much younger than previously envisaged. [ABSTRACT FROM AUTHOR]

As one of the largest Phanerozoic orogens in the world, the Central Asian Orogenic Belt (CAOB) is a natural laboratory for studies of continental dynamics and metallogenesis. This paper summarizes the research progresses of the accretionary processes and metallogenesis of the CAOB since the People's Republic of China was founded, and puts forward the prospect for future research. During the early period (1950s–1970s), several geological theories were applied to explain the geological evolution of Central Asia. In the early period of China's reform and opening-up, the plate tectonics theory was applied to explain the evolution of the northern Xinjiang and Xingmeng regions, and the opinion of subduction-collision between Siberian, Kazakhstan, and China-North Korea-Tarim plates was proposed. The idea of the Solonker-Yanbian suture zone was established. In the 1990s, the study of the CAOB entered a period of rapid development. One school of scholars including geologists from the former Soviet Union proposed a multi-block collision model for the assemblage of the CAOB. In contrast, another school of scholars, led by a Turkish geologist, Celal Şengör, proposed that the Altaids was formed through the growth and strike-slip duplicates of a single island arc, and pointed out that the Altaids is a special type of collisional orogen. During this period, Chinese geologists carried out a lot of pioneering researches on ophiolites and high-pressure metamorphic rocks in northern China, and confirmed the main suture zones accordingly. In 1999, the concept of "Central Asian metallogenic domain" was proposed, and it became one of the three major metallogenic domains in the world. Since the 21st century, given the importance for understanding continental accretion and metallogenic mechanism, the CAOB has become the international academic forefront. China has laid out a series of scientific research projects in Central Asia. A large number of important scientific research achievements have been spawned, including the tectonic attribution of micro-continents, timing and tectonic settings of ophiolites, magmatic arcs, identification and anatomy of accretionary wedges, regional metamorphism-deformation, (ultra)high-pressure metamorphism, ridge subduction, plume-plate interaction, archipelagic paleogeography and spatio-temporal framework of multiple accretionary orogeny, continental growth, accretionary metallogenesis, structural superposition and transformation, etc. These achievements have made important international influences. There still exist the following aspects that need further study: (1) Early evolution history and subduction initiation of the Paleo-Asian Ocean; (2) The accretionary mechanism of the extroversion Paleo-Asian Ocean; (3) The properties of the mantle of the Paleo-Asian Ocean and their spatiotemporal distribution; (4) The interaction between the Paleo-Asian Ocean and the Tethys Ocean; (5) Phanerozoic continental growth mechanism and its global comparison; (6) Accretionary metallogenic mechanism of the Central Asian metallogenic domain; and (7) Continental transformation mechanism. [ABSTRACT FROM AUTHOR]

The North Tianshan in NW China is a key to understanding the accretionary history of the southern Altaids. However, the tectonic setting of the North Tianshan in the Carboniferous‐Permian is debatable, and its amalgamation history is ambiguous. We report new data on the field relations, geochronology and geochemistry of Carboniferous–Jurassic volcanic rocks and sedimentary rocks from the Shichang area in order to constrain the late Palaeozoic–Early Mesozoic tectonic evolution of the North Tianshan. New LA‐ICP‐MS zircon U–Pb dates demonstrate that the Carboniferous–Permian stratigraphy is a tectonic imbrication of Carboniferous–Permian rocks and Carboniferous volcanic rocks were emplaced in Permian volcano‐sedimentary rocks. The 311 ± 2 Ma volcanic rocks are calc‐alkaline, enriched in Light Rare Earth Elements and large‐ion lithophile elements, depleted in high‐field‐strength elements, and have low initial 87Sr/86Sr ratios with positive εNd(t)(+0.3 to +8.6)values. The geochemical‐isotopic data suggest the volcanic rocks were generated in an intra‐oceanic island arc. The turbidite samples 18SC02 (~267 Ma to ~349 Ma) and 18SC09 (~299 Ma to ~369 Ma) have a relatively narrow age range with no Devonian or Precambrian peaks. Our detrital zircon data suggest the presence of a so far unrecognized intra‐oceanic arc, which was isolated from the main Yili‐Central Tianshan and Mosuowan arcs in the Shichang area of the North Tianshan during the Late Carboniferous to Permian. The compiled detrital zircon data from Carboniferous to Jurassic indicates that the North Tianshan intra‐oceanic arc was probably amalgamated with the Mosuowan arc by the Early Triassic, and then accreted to the Yili‐Central Tianshan arc by the Middle‐Late Triassic, as revealed by the changes of zircon provenance of Carboniferous, Permian, Triassic and Jurassic sedimentary rocks. All integrated data suggest that the southern Altaids most likely formed by processes of multiple subduction–accretion and convergence similar to that in the ongoing southwest Pacific. [ABSTRACT FROM AUTHOR]

The Carboniferous tectonic history of the northern West Junggar of NW China is of key importance for understanding the tectonics of the Altaids. This paper presents a systematic study of the emplacement of the E'min ophiolite, the ages of turbidites, and a stitching granite dike in order to constrain the late Carboniferous oceanic evolution of northern West Junggar. Our field investigation reveals that the Tarbagatay subduction–accretion complex formed by imbrication of turbidites and ophiolitic slices in the Western Tarbagatay Mountain, which is considered as the forearc of the Saur arc in northern West Junggar. Field relationships and zircon geochronology suggest that the emplacement of the E'min ophiolite was later than the minimum time of deposition of hanging wall turbidites, which have a zircon age of 324 Ma, and must be earlier than the crystallization time of a 311‐Ma stitching granite dike that intruded the younger turbidites. The turbidites become younger from north to south, with minimum deposition ages varying from 324 to 309 Ma. The 311‐Ma dike has an adakitic affinity suggesting that it may have formed by magma melted from a subduction slab wedge and from accreted material at ~310 Ma. Therefore, we propose an accretionary arc setting for the Saur arc, with southward migration of the trench and magma front. The 311‐Ma dike has a high Al enrichment and arc‐related geochemical signature suggesting that it was generated by melting of accreted trench sediments. This may indicate that subduction of the Saur arc may have lasted to at least the late Carboniferous. The development of such arc accretion suggests that the formation of the southern Altaids was fundamentally similar to that of accretionary orogens in the western Pacific. [ABSTRACT FROM AUTHOR]

Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past ∼500 million years. These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two. Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethyan Realm. After reappraisal of geological records of the rift, collision and subduction initiation from the surface and various geophysical observations from depth, we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic. The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards, giving birth to new oceans since the Paleozoic. The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions, which would have induced the initiation of oceanic subduction in the Tethyan Realm. Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia. The final disappearance of Neo-Tethys would have induced collision of the Gondwana-derived continents with the Eurasian continent, giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system. Therefore, the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south, into the terminal in the north. In this regard, the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) resulted from accretion during the Paleozoic subduction of the Paleo‐Asian Ocean. The Xilinhot area in Inner Mongolia is located in the northern subduction zone of the central‐eastern CAOB and outcropped a large number of late Paleozoic mafic intrusions. The characteristics of magma source and tectonic setting of the mafic intrusions and their response to the closure process of the Paleo‐Asian Ocean are still controversial. This study presents LA‐ICPMS zircon U‐Pb ages and geochemical features of mafic intrusions in the Xilinhot area to constrain the northward subduction of the Paleo‐Asian Ocean. The mafic intrusions consist of gabbro, hornblende gabbro, and diabase. Their intrusion times can be divided into three stages of 326–321 Ma, 276 Ma and 254 Ma by zircon U‐Pb ages. The first two stages of the 326–276 Ma intrusions mostly originated from subduction‐modified continental lithospheric mantle sources that underwent a variable degree partial melting (5–30%), recording the subduction of oceanic crust. The third stage of the 254 Ma mafic rocks also show arc‐related features. The primary magma compositions calculated by PRIMELT2 modeling on three samples of ∼326 Ma and two samples of ∼254 Ma show that these mafic samples are characterized by a variable range in SiO2 (47.51–51.47 wt%), Al2O3 (11.46–15.55 wt%), ΣFeO (8.27–9.61 wt%), MgO (13.01–15.18 wt%) and CaO (9.13–11.67 wt%), consisting with the features between enriched mantle and lower continental crust. The source mantle melting of mafic intrusions occurred under temperatures of 1302–1351°C and pressures of 0.92–1.30 GPa. The magmatic processes occurred near the crust‐mantle boundary at about 33–45 km underground. Combined with previous studies, it is concluded that Carboniferous to early Permian (∼326–275 Ma) northward subduction of the Paleo‐Asian oceanic crust led to the formation of the mafic magmatism in the Baolidao arc zone. The whole region had entered the collision environment at ∼254 Ma, but with subduction‐related environments locally. The final collision between the North China craton and the South Mongolian microcontinent may have lasted until ca. 230 Ma. [ABSTRACT FROM AUTHOR]

In NE Asia, the early stage (T-J) subduction history of the Paleo-Pacific oceanic plate was largely reconstructed by studies on the Heilongjiang complex, a blueschist-containing N-S trending high-pressure metamorphic belt, which is suggested to represent the "suture zone" between the Jiamusi Block and the rest of the Central Asian Orogenic Belt. However, recently more accretionary complexes with similar geochronological data were reported on both sides of the "suture zone", making the tectonic affinities of the "suture zone" unclear. Here, we select the mylonitic meta-sedimentary rocks in Huanan, one of the potential accretionary complexes near the central Jiamusi Block to reveal its depositional and metamorphic history and discuss the tectonic implications. Our results show that these rocks were deposited in/after the Late Triassic (defined by the youngest detrital zircon group) and accepted clastics from both the Jiamusi and Songliao blocks. Before the Early Jurassic (c. 178 Ma by apatite U Pb dating results in this study), they experienced high-P/low-T metamorphism (510–520 °C and 10.5–11 kbar), and then were heated to about 610 °C at 8.5–9.2 kbar during exhumation. The meta-sedimentary rocks in Huanan are components of the early Mesozoic accretionary complex in NE China. However, their present location is c. 85 km to the east of the previous proposed "suture zone" from Luobei to Mudanjiang. Considering the spatially scattering distribution of other similar accretionary complexes, such as the Zhangguangcai complex (c. 40 km to the west of the "suture zone"), we suggest that these complexes dispersedly exposed throughout NE China were either nappes transported by post-exhumation thrusting, or remnants of archipelagic oceanic crusts in the NW Paleo-Pacific region during the early Mesozoic. • Garnet micaschist in Huanan experienced high-P metamorphism in subduction channel. • Huanan complex is a Mesozoic accretionary complex near the central Jiamusi Block. • Accretionary complexes were scattered due to thrusting or archipelago ocean closure. [ABSTRACT FROM AUTHOR]

The time of final closure of the Paleotethys Ocean is still hotly debated in particular regarding the Jinsha Ocean in northern Tibet. This study reports new geochronologic, geochemical and zircon Hf isotopic data of six granodiorites-diorites, which intrude the Mid-Late Triassic Songpan-Ganzi complex (SGC). LA-ICP-MS zircon U-Pb analyses of three quartz diorites (214.9 ± 2.2, 211.0 ± 1.3, 205.8 ± 1.4 Ma) and three granodiorites (210.8 ± 2.7, 206.7 ± 3.3, 205.9 ± 3.5 Ma) gave a Late Triassic age range (214.9–205.8 Ma). These granodiorite-diorite rocks have relatively high MgO (up to 9.1%) and Mg# (up to 70.2), Al 2 O 3 , Cr, Ni, but low TiO 2 , and high magnesium andesite/diorite (HMA) chemical signatures with low Sr and Y content, and slight-moderate negative Eu anomaly. Also, the dioritic enclaves and Late Triassic detrital zircons (as young as 208 Ma) were captured by studied rocks. Hf isotope data show overall slight to moderate negative zircon εHf(t) values (−1.97 to −5.76, −4.12 to −6.72) and heterogeneous T DM C ages (1.38−1.61Ga, 1.51−1.68Ga) for quartz diorites and granodiorites respectively, together with other published Hf isotopic data in SGC, are in highly concert with those around ~240 and ~440Ma magmas (as potential sources for SGC turbidites) in east Kunlun orogenic belt. Taken together, the HMA magmas were probably derived from a reaction between subducted marine sedimentary siliceous melts and peridotites from a mantle wedge. The linear distribution of Late Triassic HMAs and their eastward-younging trend (from northern Qiangtang to southern SGC), in combination with the contrasting distribution of volcanic rocks in the northern Qiangtang terrane, lead us to suggest that a slab window opened in the downgoing oceanic crust with two diverse slab angles during oblique subduction. Accordingly, the final closure of the Paleotethys Ocean was later than 205 Ma, and most likely in the end of the Late Triassic to Early Jurassic. • Granodiorite-diorite rocks have HMA affinities and Late Triassic ages. • An eastward-younging linear belt is shown by HMAs due to a slab window. • The slab window was formed by ridge subduction with diverse subducting angles • The final closure probably occured in the end of Late Triassic to Early Jurassic. [ABSTRACT FROM AUTHOR]

The timing of the initial opening and subduction of the Palaeotethyan Ocean is currently highly debated, in particular regarding the Jinshajiang Ocean in the central Tibetan Plateau. This study presents four well‐constrained U–Pb zircon ages (422.4 ± 6.1, 336.4 ± 7.4, 272.3 ± 2.8, and 255.8 ± 3.4 Ma) of mafic blocks in the Jinshajiang Suture. These mafic blocks have a chemical oceanic island basalt (OIB) affinity. These facts, together with previously published data (236 Ma OIBs), may be interpreted as a series of seamounts/oceanic plateaux varying from Late Silurian to Late Triassic, which were accreted early in the subduction–accretion process. An andesite from the Jinshajiang Suture with continental arc characteristics yielded a zircon U–Pb weighted average age of 385.2 ± 6.6 Ma, implying that the subduction initiation may have occurred at least in the Middle Devonian. Our work suggests a long‐lived continuous accretion, which also puts an earlier initial opening time than previously thought. Taking into account the above data and integrated with relevant published information, we favour a long‐lived accretionary process accompanied with seamounts/oceanic plateaux, which provides robust new evidence for subduction‐related continental growth in the central Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The high‐pressure Heilongjiang Complex belongs to a Jurassic accretionary complex in Yilan area, NE China. The complex is located in the junction of three orogenic systems in the NE Asia: the E‐W‐striking Central Asian Orogenic Belt (CAOB), the N‐S‐striking Paleo‐Pacific system, and the ENE‐WSW‐striking Mongol‐Okhotsk system. Thus, a detailed tectono‐metamorphic analysis coupled with accurate radiometric dating of the Heilongjiang Complex provided in this study represent important evidence for understanding the complex interactions between the three orogenic systems in the Late‐Palaeozoic to Mesozoic. New structural and microstructural data combined with the strain analysis highlight the presence of three distinct deformation events affecting the high‐pressure Heilongjiang Complex. The first deformation event D1 is related to development of blueschist facies prolate to plane strain fabrics that were subsequently reworked by the blueschist‐amphibolite facies event D2 that transposed all previous structures by the main west‐dipping schistosity. This planar fabric was folded by upright F3 folds and heterogeneously reworked by greenschist facies E‐W‐striking vertical cleavage during large scale N‐S shortening. Each deformation event was related to specific strain fabrics and metamorphic conditions highlighting dynamic evolution of the subduction complex during burial, exhumation, and final shortening. The first D1 event is related to westward directed prograde constrictional flow and progressive dismembering of competent mafic, ultramafic layers, and quartzites in highly stretched meta‐sedimentary matrix. This mélange was folded by recumbent detachment folds resulting in emplacement of the exhumed unit progressively reaching amphibolite facies conditions atop of W‐WSW‐dipping channel. This event is associated with dominant flattening implying increasing mechanical coupling between the colliding Songliao and Jiamusi blocks. Subsequently, the accreted subduction complex was reworked during N‐S‐directed horizontal shortening. This event was associated with an important post‐buckle flattening of fold limbs and rotation of competent blocks with inherited D1 and D2 strain ellipsoids along F3 fold axes. Our new 40Ar‐39Ar plateau ages on muscovite and phengite (173–177 Ma), together with previous radiometric data, are interpreted as reflecting exhumation of subduction channel during the blueschist‐amphibolite facies event while the N‐S shortening (D3) probably operated in Late Jurassic as indicated by some previously published cooling ages (~140–160 Ma). The westward‐oriented subduction and exhumation fabrics of the high‐pressure Heilongjiang accretionary complex followed by N‐S‐directed upright folding are interpreted to reflect transition from E‐W Pacific subduction regime to N‐S‐directed shortening related to the closure of the Mongol‐Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

Abstract Pangea is the youngest supercontinent in Earth's history, forming about 300–250 Ma ago. As supported by large amounts of geological, paleomagnetic and paleontonlogical data, there is little debate on the positions of major continental blocks in Pangea. However, controversy has long surrounded the relations of East Asian blocks with Pangea. Most Pangea reconstructions assume that the East Asian blocks were not the components of Pangea but separated from Pangea by the Paleo-Tethys Ocean. These reconstructions were mainly based on geological and paleomagnetic data before the 1990's but did not fully consider recent data, especially for major orogenic belts that formed through the subduction and closure of the Proto-Tethys, Paleo-Asian and Paleo-Tethys oceans in East Asia. To determine where, when and how these oceans were closed, and whether or not the East Asian blocks were added to Pangea, the National Natural Science Foundation of China (NSFC) set up a NSFC Major Program entitled "Reconstructions of East Asian Continental blocks in Pangea", which started in 2012 and was completed in 2016. In the past five years, the researchers of this project carried out extensive field-based geological and paleomagnetic investigations on the East Asian blocks and their intervening mountain belts, and produced large amounts of data and competing interpretations, which provide constraints on the paleogeographic evolution of the East Asian blocks from the breakup of Rodinia to the assembly of Pangea. This forms the justification for organizing this special issue in which we collected ten papers that timely summarize these new data and interpretations and present new models for the reconstructions of the East Asian continental blocks in Pangea. [ABSTRACT FROM AUTHOR]

Abstract We integrated our new data with a review of published work on the Indo-Myanmar Orogenic Belt (IMOB) of the eastern Neotethys in Myanmar, western Yunnan (China) and Naga Hills (India), in order to better understand subduction-accretion processes of the Neotethys Ocean in SE Asia, and interactive relationships between the Gondwana and Laurasia supercontinents. From east to west, the IMOB is divided into three geographic units, the Shan-Thai Plateau, Myanmar Central Basin and Indo-Burma Range; the Mogok Metamorphic and Slate Belt is within the Shan-Thai Plateau. The Shan-Thai Plateau and eastern Myanmar Central Basin contain Paleozoic sedimentary successions, low-grade to amphibolitic facies metamorphic rocks, and the Luxi ultramafic and Myitkyina-Mogok ultramafic-diorite belts. Unmetamorphosed and metamorphosed sediments have similar detrital zircon age peaks of 1000 Ma, and 700 Ma or 500 Ma, and they are separated by the Luxi ultramafic belt, whose ε Nd (0) and 87Sr/86Sr (i) values are similar to surrounding granite, diorite and migmatite and the γOs = −4.8 ~ −8.8 is indicative of old sub-continental lithospheric mantle, rather than an oceanic suture zone. These data and relations suggest that these regions belong to the Cimmerian continental sliver, derived from the Gondwana supercontinent. The Myitkyina-Mogok ultramafic-diorite belt, located along the eastern margin of the Myanmar Central Basin that was associated with the continental sliver, contains peridotite, andesite, hornblende gabbro, diorite, granodiorite and plagiogranite, all with arc geochemical signatures and ages of 177–166 Ma. The source region of some of these igneous rocks contains a component of EM1, which is close to low 87Sr/86Sr (i) ratio of a migmatite in the Cimmerian continental sliver as shown by Sr Nd isotopes values, suggesting this belt developed as a Jurassic continental margin arc. The Mogok Metamorphic and Slate Belt contains granodiorite, diorite, tonalite, granite and migmatite extending from the Gongshan, Tengchong and Luxi areas in western Yunnan (China) to Mandalay, Kalaw, Padatchaung and Moulmein in Myanmar. These rocks have arc geochemical character and yield ages of 185–170 Ma, 128–112 Ma, 91 Ma and 75–45 Ma, suggesting development of four episodes of arc magmatism. Along the central axis of the Myanmar Central Basin there are magmatic arc-related 106–94 Ma diorite, granodiorite and tonalite, as well as Eocene and Neogene-Present (38–0 Ma) andesite, dacite, trachyte and rhyolite. Accretion took place along the central axis of the Myanmar Central Basin towards the Indo-Burma Range, and westward to the present trench axis on the margin of the Indian Ocean, as shown by westward younging of accretionary complexes and trench-slope basins. A Jurassic accretionary complex, located in the Hpakan area in the north of the Myanmar Central Basin, contains 189–147 Ma high-pressure metamorphic rocks such as jadeitite, garnet-mica schist and glaucophane schist. In the eastern belt of the Indo-Burma Range Early Cretaceous (119–115 Ma) accretionary complexes consist of upper plate Triassic unmetamorphosed and low-grade metamorphic sediments, and lower plate amphibolites, high-pressure metamorphic rocks and Jurassic-Early Cretaceous oceanic plate stratigraphy containing MORB- and OIB-type basalts and thin-bedded radiolarian cherts. Late Early Cretaceous (~100 Ma) and Late Cretaceous to Middle Eocene (75–45 Ma) trench-slope basin deposits, containing abundant fossil plants and shallow-water sedimentary structures, cover most of the Indo-Burma Range, where sediments rest with an angular unconformity on older accretionary complexes. The presence of earlier magmatic arcs, accretionary complexes and trench-slope basins suggests that the present trench on the margin of the Indian Ocean has evolved by continuous eastward subduction since the Jurassic. The magmatic arc axis migrated eastward (landward) during some time periods (Jurassic to Early Cretaceous, and Late Cretaceous to Middle Eocene) and westward (seaward) migration during others (Early Cretaceous to late Early Cretaceous, and Middle Eocene to Present), during continuous east-dipping subduction. Highlights • Indo-Myanmar Orogenic Belt develop multiple alternating forearc- and backarc-ward migration of magmatism • The long-lived subduction-accretion of Neotethys Ocean in SE Asia began in the Jurassic • Magmatic arcs and accretionary complexes occur at the eastern and western portion of the IMOB, respectively [ABSTRACT FROM AUTHOR]

Adakitic dikes are widespread in the Sawur region, northern West Junggar, northwestern China. Zircon U–Pb analyses of the dikes have yielded consistent ages of ca. 334 Ma. The dikes are characterized by relatively high SiO 2 (55.5–61.8 wt.%), Al 2 O 3 (14.5–16.3 wt.%), and Sr (468–1005 ppm), and low Y (10.1–14.1 ppm) and Yb (0.93–1.39 ppm) contents, with high Sr/Y (34–74) ratios and slight Eu anomalies, which are analogous to those of slab-derived adakites. In addition, the dikes are relatively MgO-rich (1.75–3.57 wt.%; Mg # = 44–56), with high Th/Yb ratios and positive εNd (334 Ma) (+ 6.2 to + 6.5) and εHf (334 Ma) (+ 11.3 to + 15.8) values. The data suggest that the dikes were generated by partial melting of subducted oceanic crust and overlying sediments. However, these Early Carboniferous adakitic rocks and associated I-type granites in the northern part of West Junggar are petrochemically distinct from the Late Carboniferous adakitic plutons from the southern part of West Junggar. The latter are associated with charnockites, A-type granites, tholeiites, and Nb-enriched, alkaline basalts, as well as magnesian dikes, which were generated by ridge subduction during the Late Carboniferous. The distinct lithological association of the Early Carboniferous adakites is consistent with flat slab subduction, which was characterized by anomalous heating of the slab and consequential partial melting to generate adakitic magma. After generation of the Early Carboniferous adakites, the subducting slab cooled, reverted to a more normal subduction angle in the late Early Carboniferous, and was associated with more typical I-type granite arc magmatism. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines. The Mongolia collage system was a long, N-S-oriented composite ribbon that was rotated to its current orientation when the Mongol-Okhotsk orocline was formed. The components of the Kazakhstan collage system were welded together into a long, single composite arc that was bent to form the Kazakhstan orocline. The cratons of Tarim and North China were united and sutured by the Beishan orogen, which terminated with formation of the Solonker suture in northern China. All components of the three collage systems were generated by the Neoproterozoic and were amalgamated in the Permo-Triassic. The Central Asian Orogenic Belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation, followed by two phases of orocline rotation. [ABSTRACT FROM AUTHOR]

Magmatic arcs ascribed to oceanic lithosphere subduction played a dominant role in the construction of the accretionary Central Asian Orogenic Belt (CAOB). The Beishan orogenic collage, situated between the Tianshan Orogen to the west and the Inner Mongolia Orogen to the east, is a key area to understanding the subduction and accretionary processes of the southern CAOB. However, the nature of magmatic arcs in the Beishan and the correlation among different tectonic units along the southern CAOB are highly ambiguous. In order to investigate the subduction-accretion history of the Beishan and put a better spatial and temporal relationship among the tectonic belts along the southern CAOB, we carried out detailed field-based structural geology and LA-ICP-MS zircon U-Pb geochronological as well as geochemical studies along four cross-sections across crucial litho-tectonic units in the central segment of the Beishan, mainly focusing on the metamorphic assemblages and associated plutons and volcanic rocks. The results show that both the plutonic and volcanic rocks have geochemical characteristics similar to those of subduction-related rocks, which favors a volcanic arc setting. Zircons from all the plutonic rocks yield Phanerozoic ages and the plutons have crystallization ages ranging from 464 ± 2 Ma to 398 ± 3 Ma. Two volcanic-sedimentary rocks yield zircons with a wide age range from Phanerozoic to Precambrian with the youngest age peaks at 441 Ma and 446 Ma, estimated to be the time of formation of the volcanic rocks. These new results, combined with published data on ophiolitic mélanges from the central segment of the Beishan, favor a Japan-type subduction-accretion system in the Cambrian to Carboniferous in this part of the Paleo-Asian Ocean. The Xichangjing-Niujuanzi ophiolite probably represents a major suture zone separating different tectonic units across the Beishan orogenic collage, while the Xiaohuangshan-Jijitaizi ophiolitic mélange may represent a Carboniferous back-arc basin formed as a result of slab rollback ascribed to northward subduction of the Niujuanzi oceanic lithosphere. Subduction of this back-arc basin probably took place in the early Carboniferous, generating the widespread arc-related granitoids including adakitic plutons, and overlapping earlier arc assemblages. The Beishan orogenic collage is not the eastern extension of the Chinese Central Tianshan, but it was generated by the same north-dipping subduction system separated by the Xingxingxia transform fault, as revealed by available regional data. This contribution implies that in addition to fore-arc accretion, back-arc accretion ascribed to opening and closure of a back-arc basin may also have been a common process in the construction of the CAOB, resembling that of the Mesozoic-Cenozoic subduction-accretion system in the SW pacific. [ABSTRACT FROM AUTHOR]

The Palaeozoic orogenic process in the North Tianshan of the southern Central Asian Orogenic Belt is controversial. Systematic field study indicates that the ophiolitic fragments of the North Tianshan are mainly thrust slices and blocks of a late Palaeozoic accretionary complex, which was intruded by granitoids. U-Pb zircon dating of plagiogranites from the North Tianshan ophiolite yielded a mean age of 343.1 ± 2.7 Ma. These are typical oceanic plagiogranites but with a supra-subduction zone (SSZ) signature. Ophiolitic basalts display N-MORB, E-MORB, and OIB compositions. One gabbro with an age of 301.9 ± 2.2 Ma shows E-MORB geochemistry mixed with N-MORB and OIB. Some andesites show clear island arc characters indicated by enrichment of LILEs relative to HFSEs. Mean ages of 344.9 ± 4.2 and 298.7 ± 2.4 Ma were obtained for a granite porphyry and a mylonitic granite, respectively. The two granitoids display an island arc geochemical signature evidenced by enrichment of LILEs and depletion of HFSEs. Combined with an eastward migration of Late Devonian to Carboniferous arc magmatism and related Cu-Au-Mo deposits, we propose that trench retreat and slab roll-back took place during subduction of the Junggar Ocean spreading ridge beneath the North Tianshan arc, and that the accretion may have lasted into early Permian time, an important late stage of the long-lived accretionary orogenesis in the southern Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The eastern Tiklik belt is mainly composed of meta-sedimentary rocks of the Ailiankate and Sailajiazitage Groups that were previously interpreted as Palaeoproterozoic, Mesoproterozic and Neoproterozoic stratigraphic units, which are part of the Tarim Precambrian basement. Our new detrital (U-Pb) zircon ages yield a dominant single peak with a major range between ca. 700 Ma and 800 Ma for meta-sedimentary rocks from both the Ailiankate and Sailajiazitage Groups, which demonstrates that they were mainly derived from an independent Neoproterozoic terrane. There are several ages of 444–659 Ma, of which, the youngest has an age of 444 ± 6 Ma, indicating that the time of deposition of the meta-sedimentary rocks could have been in the Early Silurian. The porphyritic granite sample has a weighted mean crystallization age of 442 ± 2 Ma. The adakite-like geochemical characteristics of the porphytitic granite suggest derivation from the melting of the oceanic slab and formation in a subduction, arc-related tectonic setting. After integration with relevant published data, our work suggests that the Ailiankate and Sailajiazitage Groups belong to a tectonic mosaic that contains Middle Neoproterozoic extensional and Paleozoic accretionary and collisional complexes, rather than the Paleoproterozoic or Mesoproterozoic basement, as previously regarded. We propose a new tectonic model for the eastern Tiklik belt that started with a Middle Neoproterozoic extension and ended with Paleozoic continuous accretion and collision in a Paleo-Tethys archipelago, which contributed to the considerable continental growth of the southern Tarim Block. [ABSTRACT FROM AUTHOR]

Abstract: Subduction-related accretion in the Junggar–Balkash and South Tianshan Oceans (Paleo-Asian Ocean), mainly in the Paleozoic, gave rise to the present 2400km-long Tianshan orogenic collage that extends from the Aral Sea eastwards through Uzbekistan, Tajikistan, Kyrgyzstan, to Xinjiang in China. This paper provides an up-to-date along-strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution. The northern part of the orogenic collage developed by consumption of the Junggar–Balkash Ocean together with Paleozoic island arcs (Northern Ili, Issyk Kul, and Chatkal) located in the west, which may have amalgamated into a composite arc in the Paleozoic in the west and by addition of another two, roughly parallel, arcs (Dananhu and Central Tianshan) in the east. The western composite arc and the eastern Dananhu and Central Tianshan arcs formed a late Paleozoic archipelago with multiple subduction zones. The southern part of the orogenic collage developed by the consumption of the South Tianshan Ocean which gave rise to a continuous accretionary complex (Kokshaal–Kumishi), which separated the Central Tianshan in the east and other Paleozoic arcs in the west from cratons (Tarim and Karakum) to the south. Cross-border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early Paleozoic to Permian as recorded by successive southward juxtaposition of ophiolites, slices of ophiolitic mélanges, cherts, island arcs, olistostromes, blueschists, and turbidites, which are mainly Paleozoic in age, with the youngest main phase being Late Carboniferous–Permian. The initial docking of the southerly Tarim and Karakum cratons to this complicated late Paleozoic archipelago and accretionary complexes occurred in the Late Carboniferous–Early Permian in the eastern part of the Tianshan and in the Late Permian in the western part, which might have terminated collisional deformation on this suture zone. The final stages of closure of the Junggar–Balkash Ocean resembled the small ocean basin scenario of the Mediterranean Sea in the Cenozoic. In summary, the history of the Altaids is characterized by complicated multiple accretionary and collisional tectonics. [Copyright &y& Elsevier]

Abstract: The southern Central Asian Orogenic Belt (CAOB) is characterized by multiple and linear accretionary orogenic collages, including Paleozoic arcs, ophiolites, and accretionay wedges. A complex history of subduction–accretion processes makes it difficult to distinguish the origin of these various terranes and reconstruct the tectonic evolution of the southern CAOB. In order to provide constraints on the accretionary history, we analyzed major and trace element compositions of Paleozoic graywackes from the Huangcaopo Group (HG) and Kubusu Group (KG) in East Junggar. The HG graywackes have relatively low Chemical Index of Alteration (CIA) values (50 to 66), suggesting a source that underwent relatively weak chemical weathering. The identical average Index of Compositional Variability (ICV) values (~1.1) for both the KG and HG samples point to an immature source for the Paleozoic graywackes in East Junggar, which is consistent with an andesitic–felsic igneous source characterized by low La/Th ratios and relatively high Hf contents. These graywackes are geochemically similar to continental island arc sediments and therefore were probably deposited at an active continental margin. U–Pb dating of detrital zircons from the lower subgroup of the HG yielded a young age peak at ~440Ma, indicating a post-Early Silurian depositional age. However, the youngest populations of detrital zircons from the KG graywackes and the upper subgroup of the HG yielded 206Pb/238U ages of ~346Ma and ~355Ma, respectively, which suggest a post-Early Carboniferous depositional age. Because of similarities of rock assemblages, these two units should be incorporated into the Early Carboniferous Nanmingshui Formation. The detrital zircon age spectrum of the Early Paleozoic HG graywackes resembles that of the Habahe sediments in the Chinese Altai, which suggests that the ocean between East Junggar and the Chinese Altai was closed before the deposition of the sediments and that the Armantai ophiolite was emplaced prior to the Early Devonian. The differences in age spectra for detrital zircons from the post-Early Carboniferous graywackes in East Junggar and the Harlik arc indicate that the emplacement of the Kalamaili ophiolite postdates the Early Carboniferous. Therefore, a long-lasting northward subduction–accretion process is suggested for the formation of East Junggar and the reconstruction of the Early Paleozoic evolution of the southern CAOB. [Copyright &y& Elsevier]

• Periods of accretionary growth happened between 305 Ma-195 Ma and 112 Ma-101 Ma. • A period of subduction erosion affected the Songliao Block from 195 Ma to 142 Ma. • The Jiamusi and Songliao Blocks were together amalgamated in the early Cretaceous. • A Jurassic-early Cretaceous extrusion event disturbed the orogenic architecture. The high-pressure Heilongjiang Complex records a long and complicated evolution from the late Paleozoic to Mesozoic in NE China, which is still subject to controversy. In this paper we present a new detailed study including structural, geochemical and geochronological analyses (Ar–Ar dating on metamorphic minerals, U-Pb SIMS dating on zircons). Two main periods of oceanward accretionary growth are identified between 305 Ma and 195 Ma and around 112–101 Ma. These periods of accretionary growth were associated with the emplacement of voluminous magmatism, slab roll-back with continental back-arc extension, and growth of a forearc accretionary prism. Between these periods of accretionary growth, a major phase of regional subduction erosion took place between 195 Ma and 142 Ma at the eastern edge of the Songliao Block. The main effects of this subduction erosion phase were that regional Jurassic-early Cretaceous extrusion overlapped with Mesozoic accretion and erosion in NE China, which disturbed the initial orogenic architecture. With a review of relevant zircon ages of this accretionary orogen, we unravel the complicated geodynamic history of accretion, subduction erosion and tectonic extrusion that shaped NE China from the late Paleozoic to Mesozoic. [ABSTRACT FROM AUTHOR]

The Beishan orogenic collage is an ideal setting for investigating the temporal and spatial relationships between extensional tectonics in the Central Asian Orogenic Belt and the rifting of Gondwana. This study presents new geochemical and geochronological data for Devonian igneous rocks and the Zhangfangshan ophiolitic mélange in the southern Beishan region. The Zhangfangshan ophiolitic mélange contains a Late Devonian gabbro block (ca. 369 Ma) with extremely depleted zircon Hf isotopic compositions (ε Hf [t] = +16.5 to +22.4). The Lucaogou diorites (ca. 367 Ma) have low MgO and compatible element contents, low Sr/Y and La/Yb ratios, and positive zircon ε Hf (t) values, indicative of derivation by dehydration melting of Mesoproterozoic mafic igneous rocks in a high-temperature and medium- to low-pressure environment. The Lucaogou K-feldspar granites (ca. 374 Ma) and Dundunshan silicic volcanic rocks (ca. 375 Ma) have A-type granite affinities, and were probably derived from magmas formed by mixing between Neoproterozoic orthogneiss-derived melts and depleted mantle-derived mafic magmas in a high-temperature shallow-crustal environment. Compiled geochronological data for subduction-related magmatism and supra-subduction zone-type ophiolites are consistent with protracted subduction–accretion until the early Carboniferous along the northern margin of the Dunhuang Block. Slab retreat in this long-lived subduction zone led to the generation of oceanic lithosphere in the southern Beishan region. Furthermore, Devonian extensional tectonics in the southern Beishan area coincided with the opening of the Paleo-Tethys Ocean, indicating that protracted subduction retreat caused the separation of the Dunhuang Block from East Gondwana. • Devonian igneous rocks were produced in an extensional setting in southern Beishan. • The slab rollback caused Devonian crustal extension in southern Beishan. • Retreating subduction caused the separation of Dunhuang Block from East Gondwana. [ABSTRACT FROM AUTHOR]

Magnesian (Mg# > 45) and/or Nb-rich (Nb > 6 ppm) dioritic-andesitic rocks have been identified in the Mayile area of southern West Junggar, Northwest China. A systematic petrological, geochronological, whole-rock geochemical, Sr–Nd–Hf isotope, and clinopyroxene chemistry study was conducted to constrain the petrogenesis, mantle source, and P–T conditions of magmas as well as the tectonomagmatic processes in the southern Paleo-Asian Ocean subduction zone. Mayile dioritic-andesitic rocks generated in the Late Carboniferous (306–312 Ma) have a high SiO 2 content (52.3–63.2 wt%) and high Mg# (46–66) as well as sanukitic-like low La N /Yb N and Sr/Y ratios. They have high Nb contents (6.27–11.6 ppm) and Nb/U (9–18) ratios and are Nb-enriched sanukitic high-Mg andesites (HMAs). Clinopyroxene thermobarometry indicates that the parental magma of the Mayile HMAs experienced a high-temperature (1137–1199 °C) and shallow-level (0.8–0.17 GPa) partial melting in a mantle wedge. They have ε Nd (t) (+5.14 to +6.42), ε Hf (t) (+8.8 to +14.4), and zircon ε Hf (t) (+9.4 to +15.8) values and a slightly high (87Sr/86Sr) t ratio ranging from 0.703214 to 0.704140 relative to normal mid-ocean ridge basalt (N-MORB). The results suggest that West Junggar was dominated by continuous records of sanukitic rocks hinting at multiple ridge subduction processes in the southern Altaids. We reconstructed the subduction history of the Junggar Ocean in the Carboniferous-Permian from these particular observations in West Junggar, and gained insight into the gradual evolution of the tectonic setting, which transitioned from normal intraoceanic subduction to hot subduction of the young oceanic lithosphere from the Early to Late Carboniferous, with subsequent ridge subduction occurring mainly in the Late Carboniferous. [Display omitted] • Mayile dioritic-andesitic rocks are Nb-enriched sanukitic high-Mg andesites. • Magma formed by a high-temperature and low-pressure partial melting. • An enriched MORB mantle component mixed with subducting sediment melts. • Southern Altaids experienced multiple ridge subductions in late Carboniferous. [ABSTRACT FROM AUTHOR]

This paper summarizes available lithostratigraphic, tectonothermal, geochronological and geophysical data to investigate the formation and evolution of the Yinshan Block, the tectonic nature of the Ordos Block, and the subduction to collision history of the Khondalite Belt, and establishes Paleoproterozoic accretion and assembly of the Western Block of the North China Craton. New critical evidence indicates that a magmatic arc developed in the Ordos Block caused by the initiation of northward slab subduction beneath the southern margin of the Ordos Block during 2.3–2.0 Ga, which contributed to the opening of the back-arc basin between the Ordos and Yinshan blocks. And then, the north margin of the Ordos Block was then transformed into a passive-type continental margin and collided with the Yinshan Block along the Khondalite Belt to form the Western Block after final closure of the back-arc basin during 1.97–1.91 Ga. Seismic data across the Western Block including a 300-km-long south-north-trending receiver function profile and a common conversion point stacking image in depth domain obviously show its crustal structure, in which the relics of two subduction slabs were preserved beneath the Ordos Block and the Khondalite Belt, respectively. Therefore, we propose a new tectonic model to help to better constrain Paleoproterozoic accretion and assembly of the Western Block in North China. [ABSTRACT FROM AUTHOR]

[Display omitted] • The augen granites in the Central Tianshan were formed at early Neoproterozoic. • The granites formed in a circum-Rodinia subduction-related extensional setting. • Central Tianshan Block had a different crustal evolution with the Tarim Craton. Neoproterozoic igneous rocks associated with the assembly and configuration of the Rodinia supercontinent are widely distributed in the Central Tianshan Block, southwestern Central Asian Orogenic Belt (CAOB), northwest China. The Central Tianshan Block is an important geological unit in tectonic reconstructions of the CAOB and Rodinia. However, the early Neoproterozoic tectonic framework and evolution of the Central Tianshan Block are poorly understood. Here we present a geochronological, mineral and whole-rock geochemical, and Nd–Hf isotopic study of early Neoproterozoic augen granites from the Bingdaban area. In situ zircon U–Pb dating shows that the augen granites have crystallization ages of 1002–992 Ma. The augen granites have high SiO 2 (70.46–76.24 wt%) and K 2 O (3.36–4.96 wt%) contents, and FeOT/(FeOT + MgO) ratios (0.76–0.84), low Mg# values (29–39), slightly enriched light rare earth element patterns, enriched large-ion lithophile elements, depleted high-field-strength elements (e.g., Nb, Ta, and Ti), and high 10,000 × Ga/Al ratios (2.3–8.3) and Zr + Nb + Ce + Y contents (256–408 ppm). The augen granites have geochemical features typical of A 2 -type granites, variable εNd (t) values of –1.64 to +6.87 and Nd model ages of 1.78–1.08 Ga, and zircon εHf (t) values of −1.96 to +6.42 with Hf model ages of 1.98–1.48 Ga. These data indicate the granites had a juvenile crustal-dominated source, with subordinate input of ancient crustal components, and formed in a subduction-related extensional setting. The extension might have been related to slab break-off beneath Rodinia. The early Neoproterozoic igneous rocks in the Central Tianshan and adjacent microcontinental blocks in the southwestern CAOB formed at or near an active continental margin, possibly part of the circum-Rodinian subduction zone during or after the assembly of Rodinia. Similar Neoproterozoic magmatism in the Central Tianshan and Yili blocks suggests that they had a comparable crustal evolution and a close tectonic and paleogeographic relationship during the Neoproterozoic. However, significant age and isotopic differences characterize the Central Tianshan–Yili blocks and Tarim Craton, suggesting that the Central Tianshan–Yili blocks were not separated from the Tarim Craton during the early Neoproterozoic. [ABSTRACT FROM AUTHOR]

Previous plate reconstruction in the Paleo-Pacific domain indicates that the Izanagi and Pacific plates influenced the NE Asian continental margin during the Mesozoic and Cenozoic, respectively. However, it remains unclear how and when the transition from Izanagi to Pacific plate subduction occurred, because most evidence came from the oceanic crust. However, the onshore geological records are poorly understood, so in order to solve this problem, we review recently-published data and identify three magmatic episodes, a magma gap and four deformation stages from ca. 95 to 30 Ma. Margin-parallel Izanagi-Pacific ridge subduction is proposed to explain the changing magmatic and deformation signatures and other regional events in the early Cenozoic. From ca. 95 to 65 Ma, the N- or NNW-directed subduction of the Izanagi plate triggered sinistral shearing along the NNE-striking faults. Arc magmas at that time incorporated older crustal materials. From ca. 65 to 55 Ma, the NWW-striking transform faults and ridge segments were subducted, developing small slab windows and facilitating the input of juvenile magmas. Local extension was active above these windows. During ca. 55 to 45 Ma, the ridge was totally subducted, and a margin-wide slab window was opened, resulting in an arc magma gap and extension. Massive asthenosphere upwelling caused the extensive accretion of juvenile materials. From ca. 45–30 Ma, the dextral NNE-trending faults resulted from the W-directed subduction of the Pacific plate. New arc magmas were generated from juvenile materials and thus are isotopically depleted. [ABSTRACT FROM AUTHOR]

NW Iran, situated between the Arabian and Eurasian plates, carries a record of both Paleo-Tethyan and Neo-Tethyan tectonic evolution. During the Wilson Cycle of Tethys Ocean opening and closing, several episodes of magmatism from Late Paleozoic to latest Cenozoic generated a massive volume of intrusive rocks. These intrusives, which record cooling histories from high-temperatures to final exhumation, are ideal for multiple geo-thermochronological studies. Our new zircon and apatite U-Pb results suggest three regional magmatic events in the Late Carboniferous, mid-Cretaceous and middle Eocene, which could be related to Paleo-Tethys subduction, Neo-Tethys subduction and Neo-Tethyan ridge subduction, respectively. New apatite fission track and (U-Th)/He data reveal post-magmatic cooling and differential exhumation related to subduction and collision. By integrating published regional thermochronological data from northeastern part of the Middle East, a broader tectono-thermal framework is outlined as follows: 1) Cretaceous cooling signals are most pronounced in the Alborz and Caucasus, and reflect back-arc extension during Neo-Tethyan subduction; 2) diachronous Neo-Tethyan evolution led to the Paleocene assemblage of Anatolia in the west, and subduction associated with a late Paleocene-Eocene magmatic flare-up in Iran. Subsequent westward escape of Anatolia and extensive surface uplift were driven by propagation of Arabia-Eurasia collision in the Miocene; 3) Continuous northward indentation of Arabia into Eurasia triggered late Miocene-Pliocene fast exhumation of the Zagros, Alborz and the Caucasus. • U-Pb data reveal three magmatic episodes in NW Iran at ∼320, ∼ 100 and ∼ 40 Ma. • Thermochronological data record post-magmatic cooling and differential exhumation. • Miocene Arabia-Eurasia collision activated uplift and westward escape of Anatolia. • Arabia indentation triggered rapid exhumation in Eurasia interior since ∼10 Ma. [ABSTRACT FROM AUTHOR]

New geochemical and U-Pb isotopic data from the Torud volcanic and subvolcanic rocks and their associated dikes exposed along the southern margin of the Sabzevar-Torud zone provide new evidence for Early-Middle Eocene, post-collision magmatism in northeast Iran. The 52–46 Ma (late Ypresian-Lutetian) U-Pb age interval of zircons separated from these rocks confirm the paleontological age of nummulite-bearing limestone interlayers. Inherited zircons separated from these igneous rocks have a much wider range of U-Pb ages that include Archean, Paleoproterozoic, Mesoproterozoic, Carboniferous, Permian, Triassic, Middle Jurassic, and Late Cretaceous. Most volcanics and subvolcanic rocks display high-K calcalkaline and shoshonitic trends. Distinct crystal fractionation patterns of the volcanic and subvolcanic rocks suggest magmatic differentiation in separate magma chambers. The studied rocks, depleted in the HFSE and enriched in the LILE, display nearly homogeneous isotopic Sr (0.7039–0.7055) and Nd (0.5126–0.5129) ratios and positive ɛNd values (0.08–0.56) indicating partial melting from an enriched lithospheric mantle source that was slightly contaminated with crustal material. Fluids, especially those released from the subducted slab, affected the composition of the source for the studied rocks. The magmatism occurred in the Torud area after the Late Cretaceous-Paleocene collision of the Central Iran microcontinent and Binalud-Kopeh-Dagh blocks and the Early-Middle Eocene break-off of the subducted slab. • Torud Early-Middle Eocene magmatism represented by volcanics, subvolcanics and dikes. • Volcanic and subvolcanic rocks show alkaline-shoshonitic and calcalkaline affinity. • Primary magmas formed by partial melting of an enriched lithospheric mantle source. • These rocks contain inherited zircons testifying for weak crustal contamination. • Igneous event postdated the collision of the Central Iran-Binalud Kopeh Dagh blocks. [ABSTRACT FROM AUTHOR]

The South Tianshan Belt has recorded the evolution of the south branches of the Paleo-Asian Ocean and is pivotal for understanding the formation of the southernmost part of the Central Asian Orogenic Belt. In order to place constraints on the tectonic evolution of the South Tianshan Ocean, three highly deformed granitic plutons (monzonitic granites, biotite K-feldspar granites and two-mica granites) exposed in the Kumishi area were collected for geochronological and geochemical studies. Zircon LA-ICP-MS U–Pb dating of the gneissic granites from the three plutons yielded crystallization ages at 446.2 ± 2.2 Ma, 431.0 ± 2.8 Ma and 407.3 ± 3.1 Ma. All of these gneissic granites have geochemical characteristics of calc-alkaline igneous rocks. The biotite monzonitic granites (446 Ma) are slightly peraluminous, LREE-enriched and show relatively flat HREE patterns mostly with negative Eu anomalies. The rocks have positive Pb and negative Nb, Ta, Ti anomalies. In combination with their negative ε Hf ( t ) values (−7.9 to −11.6) and the corresponding old T DM c ages (1.93–2.16 Ga), we suggest that the monzonitic granites were mainly derived from partial melting of the middle-lower crust dominated by Precambrian basement rocks. The biotite K-feldspar granites (431 Ma) are characterized by high K 2 O, low Fe 2 O 3 and MgO contents. They show REE patterns similar to the monzonitic granites, as well as the Nb, Ta, Ti depletions, but have more enrichment in U, Pb, Zr, and Hf. Their depleted ε Hf ( t ) values (+0.7 to +5.4) and young T DM c ages (1.07–1.37 Ga) imply significant input of mantle-derived juvenile materials, and thus suggest that the K-feldspar granites were possibly derived from a K-enriched crustal source mixed significantly with mantle-derived juvenile materials. The two-mica granites (407 Ma) show a typical S-type granite affinity with high Al 2 O 3 /TiO 2 , low CaO/Na 2 O and K 2 O/Al 2 O 3 ratios, suggesting a pelitic source. These characteristics, together with their positive ε Hf ( t ) values (−0.2 to +3.1) and relatively young T DM c ages (1.20–1.41 Ga), indicate that the two-mica granites were most likely generated by partial melting of a pelitic source with less input of juvenile materials. All of the samples from the three plutons show same geochemical characteristics of felsic magmatic rocks formed in an arc-related tectonic setting. Together with the northward thrusting tectonics and the arc magmatic rocks exposed along the South Nalati–Kawablak Fault, a northward subduction of the South Tianshan Ocean is suggested to interpret the formation of the three granitic plutons. Taking into account the distinct tectonic polarity and distribution of magmatic rocks in the western and eastern South Tianshan Belt, we suggest that the South Tianshan Ocean probably underwent different subduction processes in its western and eastern parts. A single northward subduction and a divergent bidirectional subduction are further proposed to interpret the formation of the western and eastern South Tianshan Belt, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Cambrian rhyolites (ca. 515 Ma) are recognized within the Lajishan suture. • These rhyolites were likely to be products of the oceanic arc magmatism. • The South Qilian Ocean experienced southward intra-oceanic subduction. • Intra-oceanic subduction started at ca. 530 Ma and lasted until ca. 480 Ma. The South Qilian suture in the Qilian Orogen is an early Paleozoic belt that developed as a result of closure of the southern branch of the Proto-Tethyan Ocean. It is characterized by widespread Cambrian intermediate-basic volcanic rocks which record the early-stage evolution of the paleo-ocean basin. However, Cambrian evolution of the paleo-ocean basin remains controversial due to the lack of research on the age and tectonic affinity of these volcanic rocks. In this study, we identified rhyolites from the intermediate-basic volcanic rocks in the South Qilian suture. They occur as pebbles in the breccias, or as veins and interlayers within the intermediate-basic volcanic rocks. Zircon U-Pb datings yield ages of 514.0 ± 2.8 Ma, 521 ± 4 Ma, 523 ± 5 Ma, and 513 ± 9 Ma for four rhyolites, respectively. The Cambrian rhyolites show variable La/Sm ratios and Rb contents and positive zircon ε Hf (t) values (+6.8 to +14.6) and whole-rock ε Nd (t) values (+2.1 to +4.6), suggesting that they were derived from partial melting of juvenile mafic crust. They also have high Al 2 O 3 and CaO contents, as well as low K 2 O and trace element concentrations, which are similar to those of oceanic arc rhyolite. These early Cambrian oceanic arc rhyolites, along with the SSZ-type ophiolite (ca. 530–520 Ma) to the north and late-stage granitoid intrusions (ca. 474–450 Ma), indicate that the southern branch of the Proto-Tethyan Ocean experienced southward intra-oceanic subduction during the early Cambrian-early Ordovician period. [ABSTRACT FROM AUTHOR]