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Abstract: Along active margins, tectonic features that develop in response to plate convergence are strongly controlled by subduction zone geometry. In West Junggar, a segment of the giant Palaeozoic collage of Central Asia, the West Karamay Unit represents a Carboniferous accretionary complex composed of fore-arc sedimentary rocks and ophiolitic mélanges. The occurrence of quasi-synchronous upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the West Junggar. Latest Carboniferous (ca. 300Ma) alkaline plutons postdate this early phase of folding, which was synchronous with accretion of the Carboniferous complex. The Permian Dalabute sinistral fault overprints Carboniferous ductile shearing and split the West Karamay Unit ca. 100km apart. Oblique convergence may have been provoked by the buckling of the Kazakh orocline and relative rotations between its segments. Depending upon the shape of the convergence zone, either upright folds and fold with vertical axes, or alternatively, strike–slip brittle faults developed in response to strain partitioning. Sinistral brittle faulting may account for the lateral imbrication of units in the West Junggar accretionary complex. [Copyright &y& Elsevier]

Blueschist- and eclogite-facies high- to ultrahigh-pressure (HP/UHP) metamorphic rocks occur in the southern Tianshan Belt. Their deformation and metamorphic history is important for understanding the Paleozoic tectonics of the Central Asian Orogenic Belt. Our study focuses on the structural analysis and geochronology of the HP metamorphic rocks and the surrounding rocks in the Kekesu Section in the southern Chinese Tiahshan. Geometric and kinematic analyses indicate three ductile deformation events: a top-to-the-north thrusting, a top-to-the-south shearing, and a dextral wrenching. New 40Ar/39Ar laser probe plateau ages were obtained on white mica from retrograde blueschist (316 ± 2 and 331 ± 1 Ma; lσ) and greenschist-facies metasediments (323 ± 1 Ma; lσ). These ages are interpreted as the time of retrograde recrystallization during exhumation of the HP metamorphic rocks. New structural and isotopic data, in conjunction with previous results, suggest that (1) the collision event occurred during the latest Devonian to earliest Carboniferous, resulting in HP/UHP metamorphism and the top-to-the-north thrusting; (2) the post-collisional exhumation of the HP/UHP metamorphic rocks and extensive retrograde metamorphism under greenschistfacies conditions took place in the Mid-Late Carboniferous and are correlated with south-dipping normal faulting; and (3) Permian ductile dextral shearing and associated granitic intrusion and fluid activity severely overprinted the earlier fabrics. [ABSTRACT FROM AUTHOR]

Highlights • The gneissic granites in the southern Yili Block formed during early Neoproterozoic. • Neoproterozoic granitic magma was formed by partial melting of supracrustal rocks in post-collisional setting. • The Yili Block had close affinities with the Chinese Central Tianshan and Tarim Block in Neoproterozoic. Abstract The Central Asian Orogenic Belt (CAOB) was built by amalgamation of diverse geologic units including several microcontinents. The nature and geodynamic evolution of the Precambrian basement of these units are essential to constrain their origin, and thus the geodynamic and paleogeographic reconstruction of the accretionary system. The Yili Block, located in the west of the Chinese Tianshan Orogen, is one of these Precambrian-based continental constituents. Field investigations, zircon U-Pb dating and Lu-Hf isotopic analysis, whole-rock geochemical and Sr-Nd isotopic studies were conducted on the gneissic granitoids from the Giergelang area, southern Yili Block. These rocks yielded early Neoproterozoic zircon U-Pb ages (962–934 Ma), containing substantial number of Paleo- to Mesoproterozoic inherited zircons (2403–1268 Ma); their protoliths belong to peraluminous high-K granite series displaying right-declining REE patterns and Eu negative anomalies together with LILE (K, Rb, U, Th) enrichment and depletions in Ba, Nb, Sr, P, Ti; they have negative ε Nd(t) values ranging from −2.5 to −4.7, and old Nd model ages varying from 1650 Ma to 1910 Ma; they also exhibit highly variable zircon ε Hf(t) values (−12.1 to 4.4), and Hf-in-zircon model ages (1558–2574 Ma). Integrating all these results, it is suggested that the primary magma of gneissic granitoids was generated by partial melting of supracrustal rocks with involvement of old crustal materials. A comparison of data from the Yili Block and its neighboring continental units reveals that the Neoproterozoic magmatic event is an important episode of crustal reworking for the major continental blocks within the CAOB. Similar Neoproterozoic magmatic events and comparable upper Neoproterozoic to lower Paleozoic stratigraphic sequences of the Yili, Chinese Central Tianshan and Tarim blocks, suggest that they had a similar crustal evolution and close tectonic and paleogeographic relation during Neoproterozoic, and were likely derived from one single continental plate. [ABSTRACT FROM AUTHOR]

Understanding the development and evolution of accretionary orogens is crucial for characterizing continental crust growth in time and space. In the Altaids tectonic collage of Central Asia, conflicting geodynamic models have been proposed about the Paleozoic evolution, during which juvenile continental crust has been extensively formed. This study focuses on West Junggar (NW China), a key region that has not been extensively studied yet. A multidisciplinary approach, including detrital zircon provenance study, geochemistry, and field structural analysis, provides new constraints on the evolution of three Early Paleozoic units of West Junggar. Oceanic subduction predominates in Early Paleozoic time, as indicated by ophiolltic mélanges, fore-arc volcaniclastic turbidites and magmatic arc suites. However, the development of an olistostrome supplied by a sub-contemporaneous carbonate platform, the occurrence of continental molasse, and the chronology and geochemistry of magmatic events reveal interruptions of subduction. Discrete collisions of volcanic arcs and micro-continent are inferred from the tectonic structure of the belt, which displays allochthonons units rooted in the suture zone. Early Paleozoic magmatic and sedimentary rocks of West Junggar bear some resemblance to contemporaneous analogues in Eastern Kazakhstan, and suggest a lateral connection. On the basis of these new results, we propose a geodynamic evolution in four steps: 1) Early to Middle Ordovician intra-oceanic subduction forming island arcs, 2) Late Ordovician tectonic accretion of island arcs against the Kazakhstan continental margin, 3) Early to Middle Silurian resumption of subduction and active continental margin magmatism, and 4) Late Silurian-Early Devonian micro-continent collision. This scenario, consistent with the formation of the Kazakhstan Block, supports a model of multiple episodic accretions for the Altaids tectonic collage rather than a continuous continental margin evolution. These results also suggest that, in Central Asia, continental crust growth results from alternating vertical and horizontal growth episodes throughout the Paleozoic. [ABSTRACT FROM AUTHOR]

• Protoliths of the Julideneng Metamorphic Complex were deposited between 425 Ma and 322 Ma. • Metamorphism/migmatization occurred at ~322–297 Ma in continent-based intra-arc/back-arc or post-orogenic setting. • Precambrian detrital zircons were likely derived from the Central Tianshan. • Accretionary orogeny in the North Tianshan terminated in the Permian. The North Tianshan Belt (NTB) formed by the subduction and accretion of the Junggar Ocean is a key area for reconstructing the Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt (CAOB). Despite numerous studies, the interpretation of the late Paleozoic tectonic evolution of the NTB meets no consensus yet. We conducted field investigations and LA-ICP-MS zircon U-Pb dating on metamorphic rocks from the Julideneng Metamorphic Complex (JMC) in the Harlik Range, which is located between the Turpan-Hami Basin to the south and the East Junggar Belt to the north. The metamorphic rocks are exposed in a NW-SE striking, ~10 km-wide belt and mainly composed of migmatites, garnet-sillimanite mica schists, andalusite schists, and low-grade meta-sandstones. Detrital zircons from the low-grade meta-sandstone yielded ages of 1400–1250, 1000–850, ~780, ~580, ~490, ~445 and ~425 Ma. Three micaschists contain zircon populations of 2500–2175, 1800–1600, 1500–1100, 1000–850, 800–500, ~475, ~425, 420–380, ~346 Ma, and a youngest age peak at ~322 Ma. Two samples of leucocratic dykes in migmatites yielded comparable age populations with two major peaks at 322 Ma and 297 Ma, which are interpreted as two stages of successive partial melting and anatectic melts crystallization. On the basis of structural features, zircon textures and U-Pb ages, combined with already published data, we propose that: (1) the meta-sedimentary rocks of the JMC were deposited after 425 Ma and before 322 Ma (latest Silurian to late Carboniferous); (2) the Precambrian detrital zircons in the meta-sedimentary rocks were probably derived from the Central Tianshan Block, which was once connected with the NTB; and (3) the migmatization and coeval granitic plutonism occurred at ~322–297 Ma (late Carboniferous), most likely associated with crustal thinning resulted from continent-based intra-arc or back-arc or post-orogenic extension. [ABSTRACT FROM AUTHOR]

Abstract: Whilst petrology, geochemistry and metal content of small mafic/ultramafic Ni–Cu bearing complexes have been extensively studied, their structural controls and emplacement mechanisms are still poorly documented. This study addresses the last two points with the Huangshan Ni–Cu ore belt (Chinese Eastern Tianshan) as a case study. The Huangshan intrusions are Early Permian; a period when the Tianshan orogenic belt recorded major right-lateral wrench tectonics, characterized by crustal-scale shear zones. Detailed mapping, petro-structural analysis and strain rate calculation within and around the intrusions allow us to establish that the Huangshan Ni–Cu-bearing mafic/ultramafic complexes are not layered intrusions. Instead, they emplaced by injection of several mafic/ultramafic magma batches within kilometre-scale tension gashes generated by Permian dextral shearing, and should be considered as synkinematic sheeted intrusions. Finite strain analysis across the Huangshan-Kangguer shear zone provides rather high shear strain rates (∼4.5). Considering the location and alignment of the Ni–Cu-bearing mafic/ultramafic bodies along regional shear zones throughout Eastern Tianshan, it appears that wrench tectonics most likely controlled and focussed the intrusion of parent magmas. As a consequence, rifting related to post-orogenic extension is not required to account for Permian magmatic features of the Tianshan Belt. Finally, the Huangshan Ni–Cu bearing mafic/ultramafic intrusions are neither parts of an ophiolitic suture, nor of a dunite-cored Alaskan-type ore deposit, as postulated in some previous studies. In the light of these new results, we believe that structural controls and emplacement mechanisms of many Ni–Cu sulphides deposits hosted by small intrusions (particularly funnel-shaped ones) should be (re-)evaluated from a structural and geophysical point of view. [Copyright &y& Elsevier]

Abstract: In the southern Chinese Tianshan, the southernmost part of the Central Asian Orogenic Belt (CAOB), widespread ophiolitic mélanges form distinct tectonic units that are crucial for understanding the formation of the CAOB. However, the timing of tectonic events and the subduction polarity are still in controversy. In order to better understand these geological problems, a comprehensive study was conducted on the Heiyingshan ophiolitic mélange in the SW Chinese Tianshan. Detailed structural analysis reveals that the ophiolitic mélange is tectonically underlain by sheared and weakly metamorphosed pre-Middle Devonian rocks, and unconformably overlain by non-metamorphic and undeformed lower Carboniferous (Serpukhovian) to Permian strata. The igneous assemblage of the mélange comprises OIB-like alkali basalt and andesite, N-MORB-like tholeiitic basalt, sheeted diabase dikes, cumulate gabbro and peridotite. Mafic rocks display supra-subduction signatures, and some bear evidence of contamination with the continental crust, suggesting a continental marginal (back-arc) basin setting. Zircons of a gabbro were dated at 392±5Ma by the U–Pb LA-ICP-MS method. Famennian–Visean radiolarian microfossils were found in the siliceous matrix of the ophiolitic mélange. Mylonitic phyllite which displays northward-directed kinematic evidence yielded muscovite 40Ar/39Ar plateau ages of 359±2Ma and 356±2Ma. These new data, combined with previously published results, suggest that the mafic protoliths originally formed in a back-arc basin in the Chinese southern Tianshan during the late Silurian to Middle Devonian and were subsequently incorporated into the ophiolitic mélange and thrust northward during the Late Devonian to early Carboniferous. Opening of the back-arc basin was probably induced by south-dipping subduction of the Paleo-Tianshan Ocean in the early Paleozoic, and the Central Tianshan block was rifted away from the Tarim block. Closure of the back-arc basin in the early Carboniferous formed the South Tianshan Suture Zone and re-amalgamated the two blocks. [Copyright &y& Elsevier]