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[Display omitted] • A fragmented ophiolite mélange was found along the suture zone of the Central Asian Orogenic Belt. • The ophiolite mélange underwent late Permian metamorphism. • The metamorphic P and T conditions were 8.5–8.8 kbar and 700–725 ℃, respectively. • A strong collisional orogeny occurred after the closure of the Paleo-Asian Ocean. As the largest Phanerozoic accretionary orogenic belt, whether the Central Asian Orogenic Belt (CAOB) experienced a strong collisional orogenic process after Paleo-Asian Ocean (PAO) closure remains controversial. The age and P-T conditions recorded by metamorphic rocks could be used to study the thermal and tectonic regimes during orogenic processes, providing constraints for orogenic evolution. In this paper, the geochronology and metamorphism of a newly discovered metamorphic ophiolite mélange in the Banlashan area near the Xar Moron River in the southeastern CAOB were studied. The association and age of the metamorphic ophiolite mélange protoliths are similar to those of the Xar Moron River ophiolite belt to the north. The metamorphic ages of different ophiolite mélange lithologies are all late Permian (250.2–256.5 Ma), indicating that the Siberian and Sino-Korean paleoplates collided during the late Permian. The metamorphic pressure and temperature recorded by the garnet amphibolite block in the ophiolite mélange could reach 8.5–8.8 kbar and 700–725 ℃. The core-to-rim zoning of garnet indicates that the garnet amphibolite underwent a clockwise P–T path, which is the typical metamorphic feature of collisional orogens. The ophiolite mélange metamorphic features, combined with regional magmatic, metamorphic, sedimentary and tectonic deformation data, indicate that a strong collisional orogeny occurred rather than a soft orogeny between the Siberian and Sino-Korean paleoplates after the PAO closure. [ABSTRACT FROM AUTHOR]

Voluminous granitoids are widely distributed in the Langshan region, northeast of the Alxa block, and record the evolutionary processes of the southern Central Asian Orogenic Belt. The Dabashan pluton was emplaced into the Paleoproterozoic Diebusige complex. Early Carboniferous zircon LA‐ICP MS U‐Pb ages were from 327 Ma to 346 Ma. The Dabashan pluton can be classified as monzogranite and syenogranite, and exhibits high K2O contents and K2O/Na2O ratios, which reveal a high‐K calc‐alkaline nature. The samples display strongly fractionated REE patterns, and are enriched in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). The Dabashan plutons display unusually high Ba (823–2817 ppm) and Sr (166–520 ppm) contents and K/Rb ratios (315–627), but low Rb/Ba ratios (0.02–0.14), and exhibit fertile zircon Hf isotopic compositions [εHf(t)=–14 to –20], which are comparable to those of typical high Ba–Sr granitoids. Based on the geochemical compositions of the samples, we suggest that subducted sediments and ancient crustal materials both played important roles in their generation. Basaltic melts were derived from partial melting of subcontinental lithophile mantle metasomatized by subducted sediment‐related melts with residual garnet in the source, which caused partial melting of ancient lower crust. Magmas derived from underplating ascended and emplaced in the middle–upper crust at different depths. The resultant magmas experienced some degree of fractional crystallization during their ascent. Given these geochemical characteristics, together with regional tectonic, magmatic, and structure analysis data, an active continental margin environment is proposed for the generation of these rocks. [ABSTRACT FROM AUTHOR]

The ages and origins of metasedimentary rocks, which were previously mapped as Precambrian, are critical in rebuilding the orogenic process and better understanding the Phanerozoic continental growth in the Central Asian Orogenic Belt (CAOB). The Beishan Complex was widely distributed in the southern Beishan Orogenic Collage, southernmost CAOB, and their ages and tectonic affinities are still in controversy. The Beishan Complex was previously proposed as fragments drifted from the Tarim Craton, Neoproterozoic Block or Phanerozoic accretionary complex. In this study, we employ detrital zircon age spectra to constrain ages and provenances of metasedimentary sequences of the Beishan Complex in the Chuanshanxun area. The metasedimentary rocks here are dominated by zircons with Paleoproterozoic–Mesoproterozoic age (~1160–2070 Ma), and yield two peak ages at 1454 and 1760 Ma. One sample yielded a middle Permian peak age (269 Ma), which suggests that the metasedimentary sequences were deposited in the late Paleozoic. The granitoid and dioritic dykes, intruding into the metasedimentary sequences, exhibit zircon U–Pb ages of 268 and 261 Ma, respectively, which constrain the minimum deposit age of the metasedimentary sequences. Zircon U–Pb ages of amphibolite (274 and 216 Ma) indicate that they might be affected by multi-stage metamorphic events. The Beishan Complex was not a fragment drifted from the Tarim Block or Dunhuang Block, and none of cratons or blocks surrounding Beishan Orogenic Collage was the sole material source of the Beishan Complex due to obviously different age spectra. Instead, 1.4 Ga marginal accretionary zones of the Columbia supercontinent might have existed in the southern CAOB, and may provide the main source materials for the sedimentary sequences in the Beishan Complex. [ABSTRACT FROM AUTHOR]

[Display omitted] • Late Neoproterozoic ophiolite fragments were discovered in the Irshi area. • The early Paleozoic crust of the middle Great Xing'an Range is an orogenic belt. • Neoproterozoic–early Paleozoic lateral crustal growth occurred in the eastern CAOB. The tectonic affinity of the middle segment of the Great Xing'an Range (GXR) in NE China has become one of the focus issues about the Paleozoic crustal division and tectonic evolution of the eastern segment of the Central Asian Orogenic Belt. In this paper, we identified some ophiolite fragments from the early Paleozoic strata in the Irshi area of the middle segment of the GXR, which was previously thought to be the interior of the Precambrian Xing'an block. These ophiolite fragments and the surrounding deformed clastic rocks together constitute the Irshi ophiolite mélange (IOM). Zircon U-Pb dating reveals that the ophiolites formed during 603–608 Ma, which indicates that there was an oceanic basin during the late Neoproterozoic. The geochemical composition suggests that the ophiolites were formed in a back-arc setting. The youngest group of detrital zircons in the matrix ranges from 435 Ma to 480 Ma. In addition, the IOM was covered unconformably by late Silurian and Devonian strata, and it was thus likely emplaced during the early–middle Silurian. The identification of the IOM eliminated the possibility that the middle segment of the GXR was an independent Precambrian continental block. The spatial–temporal distribution of Proterozoic–early Paleozoic ophiolite, metamorphic complexes, and magmatic and sedimentary rocks in the middle segments of the GXR indicates that the tectonic affinity of the late Neoproterozoic–early Paleozoic crust in this area is an accretionary orogenic belt. The continuous subduction of the Paleo-Asian Ocean was responsible for the formation of the orogenic belt. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Jiangnan orogenic belt delineates the suture zone between the Cathaysia and Yangtze blocks of the South China Craton. The western part of the belt, in the Longsheng region, consists of a disrupted mafic-ultramafic assemblage of pillow basalt, gabbro, diabase, and peridotite along with siliceous marble, ophicalcite, and jasper mixed with basalt. Significant talc deposits occur on the margins of the ultramafic bodies as well as in the transition zone between marble and basalt. Primary rock relations are largely overprinted by pervasive shearing, resulting in disruption of the assemblage into series of discontinuous blocks within a phyllite matrix. West-dipping thrust faults mark the eastern contact of blocks, and the overall succession has the appearance of a tectonic mélange. U-Pb zircon age data from the gabbros and diabases yield crystallization ages of 867 ± 10, 863 ± 8, and 869 ± 9 Ma, with positive εHf(t) values. The gabbro, basalt, serpentinite, and some talc samples display minor light rare earth element–enriched patterns with obvious depletion of Nb and Ta, indicating a subduction-related setting. The tuffaceous phyllite shows similar geochemical features. A few mafic rocks and the altered ultramafic rocks display mid-ocean ridge basalt (MORB) affinity. Overall lithostratigraphic relationships, age data, and geochemical signatures suggest a forearc setting that was imbricated and disrupted within an accretionary prism environment to form an ophiolitic mélange. The pillow basalt, red jasper, and MORB-type mafic-ultramafic rocks within the mélange occur as exotic blocks derived from the subducting oceanic plate, whereas the arc-type mafic rocks occur as autochthonous blocks, which are all exposed in a matrix of sandy and tuffaceous phyllite. [ABSTRACT FROM AUTHOR]

The Late Paleozoic tectonic evolution of the southeastern Central Asian Orogenic Belt (CAOB) has long been controversial, and one of the most contentious issues has been whether there was a collisional orogenic event during the Middle Paleozoic. Here we report the discovery of a Late Devonian (373.5 ± 6.8 Ma) ophiolite fragment in the Diyanmiao mélange of southeastern Inner Mongolia. This fragment, coupled with previously reported Carboniferous ophiolites in the same region, confirm the former presence of a Late Devonian ocean basin that evolved into the Carboniferous basin. The geochemical characteristics of the Devonian and Carboniferous mafic rocks in the ophiolites are consistent with evolutionary trends from mid-ocean ridge (MOR)-like to supra-subduction zone (SSZ) compositions. The presence of a Late Devonian-Carboniferous trench-arc-basin system in the region, which is represented by the Daqing-Diyanmiao and Bayan'aobao-Hongger ophiolite belts, the Baolidao arc, and the Erenhot-Hegenshan Oceanic Basin (EHB), confirms the presence of a late Devonian-Carboniferous orogenic belt in the southeastern CAOB. The western segment of the Baolidao arc was developed on continental basement (the Xilin Gol complex), whereas the eastern segment was formed on oceanic basement. This tectonic configuration is similar to that of the modern Aleutian arc, Kamchatka-Kuril Islands and Japan-Ryukyu arc system in the northern and western Pacific Ocean. During the early Permian the oceanic basin represented by the Erenhot-Hegenshan basin closed, and the Baolidao arc was accreted onto the southern continental margin of the Southern Mongolian continental block. • Late Devonian ophiolite fragments are discovered in the Diyanmiao mélange. • The Diyanmiao ophiolites formed in a forearc setting. • The Paleo-Asian Ocean did not close before the Late Devonian. [ABSTRACT FROM AUTHOR]

As the largest accretionary orogen, the crustal tectonic framework and evolution of the Central Asian Orogenic Belt (CAOB) have always been one of the hot topics among geologists (Sengör et al., 1993, 1996; Jahn et al., 2000a; Badarch et al., 2002; Windley et al., 2007; Li et al., 2009). The formation of the main part of the crust in the CAOB involved continuous lateral accretion of island arcs and accretionary complexes along the margins of the Siberian, Sino‐Korean and Tarim paleo‐continents and the final collision between these continental margins because of the subduction of the Paleo‐Asian Ocean plate since Mesoproterozoic. The ophiolites, which represent the fragments of ancient oceanic lithosphere, are the direct evidence for the study of the evolution of orogenic belts. Based on field geological survey, the mantle peridotite (serpentinite), gabbro, basalt and radiolarian bedded chert, which were deemed as the "ophiolite trinity", were identified as isolated blocks in the matrix of pelitic siltstone and silty mudstone in the Kedanshan, Xingshuwa and Jiujingzi areas along the Xar Monron River in southeast Inner Mongolia of China. Besides, there were plenty of other exotic blocks, such as limestone and sandstone, in the matrix. Both of the matrix and blocks underwent strong foliated deformation. All of these rocks above constitute a tectonic mélange. Zircon U‐Pb dating for the gabbro blocks in the Xingshuwa and Jiujingzi ophiolites reveals that they were formed in early Permian (275–280 Ma). The ages of the gabbros, together with the middle Permian radiolaria fossils in the chert reported by Wang and Fan (1997), indicate that the oceanic basin was not closed in early‐middle Permian. The geochemical compositions of the basaltic blocks distributed in different locations in the Xingshuwa tectonic mélange display different genetic types of normal mid‐ocean ridge basalt (N‐MORB), enriched mid‐ocean ridge basalts (E‐MORB), oceanic island basalt (OIB), island arc basalt and continental marginal arc basalt, which indicates what they represented is a complex oceanic basin. Combining with the studies on regional magmatism, strata and structure data, it is suggested that the Xar Moron River Ophiolite belt represented the final suture zone of the Paleo‐Asian Ocean in the southeast Inner Mongolia, and the ocean did not close before late Permian. [ABSTRACT FROM AUTHOR]

Abundant Permian magmatism is exposed in the southern Beishan Orogenic Collage, and records key details on the closure of the Paleo-Asian Ocean. The Xiaoxigong granites, exposed in the southern Beishan orogen, exhibit middle Permian zircon U Pb ages (269–267 Ma). They are sodium-rich and exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y (99–120) and (La/Yb) N (41–66) values. The Xiaoxigong granites are depleted in whole-rock Nd isotopes [ε Nd (t) = +4.2 to +4.5] and zircon Hf isotopes [ε Hf (t) = +4.3 to +11.4]. Geochemical compositions show that the Xiaoxigong granites formed by partial melting of the subducted Liuyuan oceanic slab, and subducted sediments also played important roles. Two types of dikes were identified in the early Permian host granite (~280 Ma) in the Yinwaxia area. The Group I dikes (267 Ma) are calc-alkaline gabbros, exhibit some subduction-derived geochemical imprints, and are interpreted as derived from an E -MORB-like source that was metasomatized by subduction-related fluids; the Group II dikes are sodium-rich, calc-alkaline diorites, and exhibit high MgO (5.45–6.73 wt%) and compatible element contents, and depleted isotopic compositions. They are sanukitic high-Mg diorites derived from interactions between melts of subducted sediments and overlying mantle peridotites. The association of contemporaneous high-Mg dioritic dikes, arc-like gabbroic dikes, and adakitic granites indicate middle Permian oceanic slab subduction in the southern Beishan. Furthermore, we propose that a subducting oceanic slab window can account for Permian magmatism in the Shibanshan unit, and that the final termination of the Paleo-Asian Ocean in the southern Beishan occurred after the middle Permian. • Middle Permian adakites, high-Mg diorites and arc-like gabbros are reported. • A middle Permian oceanic slab subduction is proposed in the southern Beishan. • The Permian magmatism was formed in an oceanic slab window in the southern Beishan. [ABSTRACT FROM AUTHOR]

The Jiangshan-Shaoxing fault zone lies along the SE margin of the Jiangnan belt, and delineates the northeastern margin of the Cathaysia Block of the South China Craton. At Shijiao in NE Zhejiang, the fault zone consists of hornblende schist intruded by migmatized quartz diorite. It constitutes a shear zone delineating the welded boundary between the Neoproterozoic Shuangxiwu Group of Jiangnan belt to the north and the Chencai Complex of Cathaysia Block to the south. The Shuangxiwu Group is composed mainly of basalt, andesite and flysch, whereas the Chencai Complex contains magmatic and sedimentary rocks that experienced amphibolite facies metamorphism. Zircons from quartz diorite and gabbro from the fault zone at Shijiao yield ages of 854 ± 6 Ma, 857 ± 5 Ma and 860 ± 5 Ma, with positive ɛHf( t ) values of 7.81–11.8 and 4.57–10.39. The quartz diorite and mafic-ultramafic rock samples display minor LREE enriched pattern with obvious depletion of Nb, Ta, Rb, Ba and Ti, compared to their neighboring elements and plot in the volcanic arc field on geochemical diagrams, similar to that of volcanic rocks from Shuangxiwu Group. Overall relationships within the Jiangshan-Shaoxing fault zone at Shijiao suggest the ca. 860–850 Ma rock suites were generated in a convergent plate margin and are part of the Jiangnan belt, and not the Cathaysia Block, thus constraining the location of the suture between the two lithotectonic units in NE Zhejiang area during Neoproterozoic. [ABSTRACT FROM AUTHOR]

The Jiangnan orogenic belt in South China defines a subduction-collisional zone between the Yangtze and the Cathaysia blocks. The eastern part of this belt comprises the oceanic Huaiyu terrane, the northeast Jiangxi suture zone and the continental Jiuling terrane. We report zircon U–Pb and Hf isotope data and whole rock geochemistry on the arc magmatic rocks of andesite and basalt occurring as olistostromal blocks, as well as conglomerate in the Dengshan Group above the unconformity between cover sequence and the volcanic arc units. The andesites yield weighted mean ages of 864 Ma, 868 and 871 Ma, whereas the detrital zircons from the conglomerate yield a major age population of 863–810 Ma (peak of 833 Ma), with two minor ones of 1120–940 Ma (peak at 960 Ma) and 1780–1560 Ma (1670 Ma). A post-ca. 810 Ma depositional age is thus suggested for the Dengshan Group. The influx of olistostromal deposits into the Dengshan Group must post-date the youngest detrital zircon age of 810 Ma and is possibly related to the widespread Nanhua rifting associated with the breakup of Rodinia. Furthermore, the age distribution of detrital zircons from the phyllite associated with the arc units compared to its depositional age also suggest a convergent setting, and those from the conglomerate are plotted into a similar field. The andesite and basaltic trachyandesite have LREE enriched patterns, with minor negative Eu anomaly, and negative Nb, Ta, Cs and Ti anomalies. However, the basalt displays only minor LREE enrichment, with no Eu anomaly, and almost flat spidergram trace element patterns, except for a minor positive Sr, Ba and Ti anomaly and negative Rb anomaly. The andesite and basaltic trachyandesite are all plotted in the field of volcanic arc, suggesting an arc setting. The basalt is plotted between EMROB and volcanic arc domains, suggesting magma generation from metasomatised sub-arc sources with subducted oceanic components. The Hf isotopic data on zircons from the andesite yield positive ɛ Hf( t ) values of 2.79–15.51 and late Mesoproterozoic model ages, suggesting that the Neoproterozoic arc sources include reworking of subducted late Mesoproterozoic materials. Our results show that the amalgamation of the Yangtze and Cathaysia blocks in the eastern part occurred at some time between ca. 864 Ma and ca. 810 Ma. [ABSTRACT FROM AUTHOR]

Abstract: The Central Tianshan, which is proposed to be part of the Tarim Block during Precambrian time, holds a pivotal role in the evolution of the Central Asian Orogenic Belt. In this study we employ detrital zircon age spectra to probe the Precambrian history of the region and to evaluate the link with the Proterozoic supercontinents. Detailed U–Pb zircon age data are reported for detrital zircons from Neoproterozoic metasedimentary rocks in the Baluntai region, the heartland of Central Tianshan. The metasediments here are dominated by zircons with major age populations of 2544–2394Ma, 1900–1500Ma, 1070–752Ma, ca. 560Ma and ca. 445Ma. The 2544–2394Ma ages correlate with the generation of continental nuclei in Tarim. The tectonothermal events during the periods of 1900–1500Ma and 1070–752Ma correspond to the assembly and breakup of the Columbia and Rodinia supercontinents. The magmatic ages represented by the age peak at ca. 560Ma correlate with those reported from the Late Neoproterozoic–Cambrian orogens in different fragments of the Gondwana supercontinent. The youngest age peak of ca. 445Ma is interpreted to represent the Caledonian orogenic event in Central Tianshan that is linked to the history of the Central Asian Orogenic Belt. Recyling of ancient crustal materials dominated, with minor input of juvenile materials during the above time intervals, with exception at ca. 2460Ma when significant addition of juvenile material occurred. A combination of U–Pb dating and Hf-isotope data in our study reveals that Central Tianshan was a part of the Tarim Block. [Copyright &y& Elsevier]