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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]

Zircon U-Pb-Hf isotopes, integrated with bulk-rock major, trace element, and isotopic compositions of amphibolites from the Makran ophiolitic mélange complex (OMC), carry implications on the evolution of the Neo-Tethys Ocean. Field and petrographical-geochemical data confirm these amphibolites as products of the metamorphism of a mafic protolith. Zircons from the amphibolites have U-Pb ages of Late Early Permian (273 Ma) to Late Triassic (210 Ma), and their εHf(t) values vary from +6.32 to +15.4. The Makran amphibolites are geochemically similar to transitional- or enriched-MORBs. The 143Nd/144Nd(t) ratios for amphibolites range from 0.51260 to 0.512551, and 87Sr/86Sr(t) from 0.704433 to 0.706244. The Pb-isotope composition of these rocks is radiogenic, ranging from 15.61-15.64 for 207Pb/204Pb(t), 18.98-19.21 for 206Pb/204Pb(t) and 38.88-39.36 for 208Pb/204Pb(t). The isotopic and geochemical signatures of these rocks suggest that they were most likely formed during continental rifting and originated from a relatively enriched mantle source. This is also attested by their high zircon Ce/Ce* ratios. We interpret these amphibolites related to the Permian-Triassic plumes that triggered Gondwana rifting to open the Neo-Tethyan Ocean before metamorphosed, fragmented, and accreted into the Makran accretionary complex probably during Early to Late Cretaceous time. [ABSTRACT FROM AUTHOR]

Early Palaeozoic evolution of the Kazakhstan orocline in the Central Asian Orogenic Belt (CAOB) is key to reconstructing the Palaeozoic tectonic framework in Central Asia. This study presents field mapping, geochemistry, and geochronological data from the Wulasitai area of northern West Junggar to constrain the subduction polarity and major tectonic events in the Chingiz arc of the Kazakhstan orocline during the Early Palaeozoic. The mapping area outcrops imbricated coherent turbidite slices and mélanges that consist of chert, limestone, silt, sandstone, and conglomerate blocks in mudstone matrix, representing an OPS (Ocean Plate Stratigraphy) mélange in an accretionary complex. Existing fossil ages from these blocks range from the Ordovician to Silurian, while our new detrital zircon U-Pb samples from the turbiditic matrix yield maximum depositional ages (MDTs) from 428 ± 2 Ma to 450 ± 1 Ma. Detrital zircon ages of ~510 to 430 Ma in the mélange suggest the Chingiz arc to the south of the study area as a major sediment source, providing an indirect constraint on the polarity of subduction. We suggest that the northern part of the Chingiz arc may be underlain by southward subduction, with the accretionary complex located on the Wulasitai area of the northern West Junggar. The Wulasitai mélange is overlain depostionally by volcanic rocks carrying depleted HFSE and enriched LILE, LREE. The andesite and tuff are dated to 415 ± 5 Ma, 414 ± 3 Ma, and 402 ± 6 Ma, which we interpret as reflecting the development of the volcanic arc onto the previous subduction complex. This model implies the generation of the arc (accretion arc) as the slab rolling back and trench retreating, which may play an important role in the evolutionary history of CAOB. [ABSTRACT FROM AUTHOR]

A major current debate in Asian tectonics concerns the time of closure of the Paleo‐Asian Ocean (PAO) and the collision between the Central Asian arcs and the Tarim and North China cratons (NCC). This has led to much uncertainty about the reconstruction of proto‐Asia and tectonic configuration of northeast Pangea. Here we report Triassic provenance change in the foreland of the Alxa Block by field‐based zircon U‐Pb and Hf isotopic analysis. Nonmarine sediments, unconformable on or in fault contact, with the Alxa basement yield Precambrian and Paleozoic–Triassic detrital zircon ages with maximum depositional ages of Middle‐Late Triassic (∼244–224 Ma). Hf isotopic data indicate that Middle Triassic sandstones were sourced from the NCC basement and a continental arc, whereas Late Triassic sediments received an additional input from a juvenile arc. This provenance change in the foreland sedimentation indicates that the final closure of the PAO was in the Middle‐Late Triassic. Plain Language Summary: The Central Asian Orogenic Belt, the world's largest Phanerozoic accretionary orogen, was constructed by the amalgamation of magmatic arcs and subduction‐accretion complexes during the protracted subduction of the Paleo‐Asian Ocean (PAO). The collision between Central Asian arcs and the Tarim and North China cratons led to the final closure of the PAO and formation of proto‐Asia and northeast Pangea. Constraining when and how the PAO closed is fundamental for a better understanding of the complex history of assembly of this part of Asia and the process from accretion to collision of the accretionary orogen. We conducted geological mapping and provenance analysis of a newly discovered foreland deposition on the Alxa Block in northwest China. The results reveal a provenance change in the Middle‐Late Triassic, which we interpret as a response to collision between the juvenile Central Asian arcs and the North China Craton. Our findings combined with regional data point to final closure of the PAO in the Middle‐Late Triassic. Key Points: Discovery of Triassic syn‐orogenic sediments in the foreland of the Alxa Block, northwest ChinaDetrital zircon U‐Pb and Lu‐Hf isotopic data indicate that juvenile Central Asian arc detritus arrived in the Alxa foreland by CarnianThe provenance change constrains the time of closure of the Paleo‐Asian Ocean as Middle‐Late Triassic (Ladinian‐Carnian) [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]

The interaction of the Palaeo-Pacific and Palaeo-Asian Oceans is an enigmatic issue as their temporal and spatial features are controversial. To address this issue, we present a systematic study of large volumes of early Permian volcanic rocks and intrusions developed in the East Tianshan. The represented samples of basaltic andesites and rhyolites yield zircon crystallization ages of 285.1 ± 5.9 Ma and 275.3 ± 1.8 Ma, respectively. The basalts have normal mid-ocean ridge basalt (N-MORB) and arc-related geochemical signatures with high TiO2 contents, negative Rb, Th, U, Nb and Ta anomalies and positive Eu anomalies. Basaltic andesites and andesites have arc-related geochemical characteristics with moderate TiO2 contents and relatively negative Nb, Ta and Ti anomalies, together with slightly negative to positive Eu anomalies. The rhyolites show an affinity with A2-type granite with high SiO2, K2O + Na2O, Fe/Mg, Ga, Zr, Nb, Y, HFSE, REE and Y/Nb levels (>1.2). These geochemical data suggest that the rocks formed in a supra-subduction zone. The presence of high ϵNd(t) values of +4.6 to +8.2 and low (87Sr/86Sr)i (0.70342–0.70591) values indicates that the volcanic rocks originated from a depleted mantle. We propose that oblique subduction with slabs breaking off gave rise to transtension and to the emplacement of large volumes of mantle-derived melts in the early Permian in the East Tianshan, serving as an important record of the subduction zone of the Palaeo-Pacific Ocean. [ABSTRACT FROM AUTHOR]

There is a broad consensus that the final closure of the Paleo‐Asian Ocean lead to the formation of the southern segment of the Central Asian Orogenic Belt. However, the final closure of the Paleo‐Asian Ocean remains controversial. To address this issue, a systematical study of geochemical and zircon U–Pb on the Kawabulak ophiolite in the southern Eastern Tianshan was carried out. The Kawabulak ophiolite is an accretionary prism that consists of different lithological tectonic slices and marks the suture zone that welded the Central Tianshan composite arc and the northern passive margin of the Tarim Craton. Zircon U–Pb data show that gabbro blocks of the Kawabulak ophiolite formed at 360.9 ± 3.3 Ma in the northern part and 326.0 ± 3.3 Ma in the southern part, respectively. The geochemistry features of basalts and gabbros show OIB‐type, arc/subduction‐related affinities, indicating different tectonic setting origins. A granitic gneiss with an arc‐related geochemical feature yielded a zircon U–Pb age of 477.2 Ma, indicating the earliest subduction event. The youngest deformed arc‐related granitic intrusion (295 Ma) in the Kawabulak prism indicates that the final closure timing of the Paleo‐Asian Ocean in Eastern Tianshan is after the Early Permian. The results of our study shed light to the temporal and spatial evolution of the southern Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The Altai‐Junggar‐Tianshan collage in southern Altaids is an important metallogenic domain in Central Asia that contain world‐class copper‐iron‐nickel deposits. As an accretionary‐type metallogenic system, the metallogenic processes of the Altai‐Junggar‐Tianshan collage is essential in understanding the genetic mechanism of ore deposits in general. Here in this paper we present a brief introduction to the project on the western part of the Southern Altaids, entitled "The deep structure and metallegenic processes of the North China accretionary metallogenic systems". This project mainly focuses on the deep structure and metallogenic background of the Altai‐Junggar‐Tianshan collage by integrated studies from field geology, structural mapping, geochemistry and geophysical exploration. Multiple new geological and geophysical methods will be applied to make transparency of the Kalatongke and Kalatage ore clusters. This will update our understanding of the geodynamic processes of metallogenesis and lead to the development and foundation of new metallogenic theories in accretionary orogens. [ABSTRACT FROM AUTHOR]

The closure of the Paleo-Asian Ocean (PAO) is crucial for understanding the late Paleozoic–early Mesozoic paleogeography of Proto-Asia and the tectonic configuration of NE Pangea. However, the timing and mechanism for the PAO closure and final amalgamation of the Central Asian Orogenic Belt (CAOB) remain highly controversial. Available studies argue either for a pre-Carboniferous closure or eastward, scissor-style diachronous closure from late Carboniferous to late Permian. This ambiguity is mainly caused by the different criteria applied to evaluate the final closure of oceanic basins and termination of accretionary orogenesis. Here we summarize new evidence including the youngest mélange-bearing accretionary complex and provenance change of syn-orogenic sediments in order to trace the terminal closure of the PAO from Tianshan in the west, through Beishan and Alxa, to Solonker and Changchun-Yanji in the east, a total distance of ∼5000 km. The Tianshan marks the demise of the western segment of the PAO where the Tarim Craton collided with the Kazakhstan–Yili–Central Tianshan arc. Several ophiolitic mélanges from the Kyrgyz and Chinese Tianshan show the relicts of Permian–Triassic oceanic lithosphere that amalgamated during the Middle-Late Triassic. In Beishan, three ophiolitic mélanges contain Permian igneous rocks and Permian–Triassic sedimentary matrix, suggesting closure of the ocean between ∼245–222 Ma. In the Engger Us mélange of Alxa, a turbidite matrix overlying Permian ocean plate stratigraphy yields a ∼244 Ma maximum depositional age, constraining the time of emplacement of the accretionary complex. To the east, several ophiolitic mélanges in Inner Mongolia contain Permian–Early Triassic gabbro/basalt and middle-late Permian radiolarians, suggesting subduction-accretion continued into the Early Triassic. Along the Changchun–Yanji suture in NE China, several accretionary complexes yield emplacement ages of ∼246–234 Ma. Therefore, the youngest ophiolitic mélanges and accretionary complexes across the whole southern CAOB were formed during the Middle-Late Triassic. In addition, Middle-Late Triassic provenance changes have been identified in syn-orogenic sediments in Tianshan, Beishan, Alxa, Inner Mongolia and NE China. These data are in agreement with Triassic deformation and high-pressure metamorphism, which together indicate that the western, central, and eastern segments of the PAO were closed almost contemporaneously during the Middle-Late Triassic. To the south, multidisciplinary data suggest that the amalgamation between South China, Sibumasu, Indochina, Qiangtang, and North China took place between ∼230–225 Ma, which led to the closure of the Paleo-Tethys Ocean. Taken together, the Indosinian orogeny leading to the amalgamation of the East Asian blocks marks the final assembly of Pangea. The joining of East Asia in the Late Triassic maximized the land area of Pangea, which potentially fostered the dramatic climate change and formation of the megamonsoon. • Permian–Triassic ophiolitic mélanges and accretionary complexes in the southern Central Asian Orogenic Belt are reviewed. • Contemporaneous closure of the western, central and eastern segments of the Paleo-Asian Ocean in the Middle-Late Triassic. • Middle-Late Triassic orogenesis in East Asia marks the final assembly of Pangea. [ABSTRACT FROM AUTHOR]

Abstract The architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components, but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined, because of unavailable data. The Central Asian Orogenic Belt (CAOB) provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage. In this paper we review several lines of available evidence, which enable us to propose a new tectonic model of huge roll-back in the formation of the accretionary tectonics of the Mongolian collage in Central Asia. In the early Paleozoic the Mongolia collage comprised the southern Siberian and the Tuva-Mongol Oroclines. The Siberia Craton and the Mongolia collage jointly formed a giant "tadpole-shape" within the Paleo-Asian and Panthanlassic oceans; its head (Siberia) was to the south, and the tail (Tuva-Mongol) to the northwest. The structures and tectonic zonation of the Mongolia collage are characteristic of multiple arcs, which have been separately described in detail in different segments southwards from the Southern Siberia-East Sayan, West Sayan-Gorny Altai-Chara, via the Lake Zone-Junggar-Tianshan, Gobi Altai-Beishan-Alxa, to the Manlay-Hegenshan-Baolidao-Solonker segments. Almost all segments underwent Early Paleozoic to Permian, or even Triassic, frontal subduction and accretion, while rifting in the Late Carboniferous to Permian or Triassic occurred in the outward/oceanward (westward) advancing Mongolian collage. Therefore, we suggest that a huge complex roll-back, active from the Carboniferous to Permian or even to late Triassic, facilitated the formation of the Mongolian collage. The outward multiple roll-back process was compatible and almost coeval with the start of the Tuva-Mongol Orocline and rotation of the Siberian Craton, as confirmed by paleomagnetic and structural data. During the roll-back processes an archipelago paleogeography was formed behind the frontal subduction and accretion, in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times. The roll-back process was affected by the collision of the Kazakhstan collage along the Chara and Karamay zones in the Early Permian, the collision of the Tarim Craton along the South Tianshan zone in the Early Permian, the collision of the Dunhuang Block along the Liuyuan zone in the Early Permian-Triassic, the collision of the Alxa block along the Qugan Qulu zone in the Permian, and the collision of the North China Craton along the Solonker zone in the Middle-Late Triassic. The tectonic styles and architecture of accretionary orogenic belts like the CAOB are characterized both by the amalgamation of multiple terranes and by oroclinal bending. The systematic anatomy of the multiple roll-back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens. [ABSTRACT FROM AUTHOR]

The anatomy of an ancient accretionary complex has a significance for a better understanding of the tectonic processes of accretionary orogens and complex because of its complicated compositions and strong deformation. With a thorough structural and geochronological study of a fossil accretionary complex in the Atbashi Ridge, South Tianshan (Kyrgyzstan), we analyze the structure and architecture of ocean plate stratigraphy in the western Central Asian Orogenic Belt. The architecture of the Atbashi accretionary complex is subdivisible into four lithotectonic assemblages, some of which are mélanges with “block-in-matrix” structure: (1) North Ophiolitic Mélange; (2) High-pressure (HP)/Ultra-high-pressure (UHP) Metamorphic Assemblage; (3) Coherent & Mélange Assemblage; and (4) South Ophiolitic Mélange. Relationships between main units are tectonic contacts presented by faults. The major structures and lithostratigraphy of these units are thrust-fold nappes, thrusted duplexes, and imbricated ocean plate stratigraphy. All these rock units are complicatedly stacked in 3-D with the HP/UHP rocks being obliquely southwestward extruded. Detrital zircon ages of meta-sediments provide robust constraints on their provenance from the Ili-Central Tianshan Arc. The isotopic ages of the youngest components of the four units are Late Permian, Early-Middle Triassic, Early Carboniferous, and Early Triassic, respectively. We present a new tectonic model of the South Tianshan; a general northward subduction polarity led to final closure of the South Tianshan Ocean in the End-Permian to Late Triassic. These results help to resolve the long-standing controversy regarding the subduction polarity and the timing of the final closure of the South Tianshan Ocean. Finally, our work sheds lights on the use of ocean plate stratigraphy in the analysis of the tectonic evolution of accretionary orogens. [ABSTRACT FROM AUTHOR]

• 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]