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Abstract: The western Kunlun orogen, the northwest Tibet Plateau, occupies a key tectonic position at the junction between the Pan-Asia and the Tethyan tectonic domains. It is related to subduction of Proto- and Paleo-Tethys and terrane collision from early Paleozoic to early Mesozoic. This paper presents the first detailed SHRIMP zircon U–Pb chronology, mineral chemistry, major and trace element, and Sr–Nd–Hf isotope geochemistry of three Middle Triassic plutons (Yuqikapa, Muztaga and Taer) and their microgranular enclaves in the western Kunlun orogen. SHRIMP zircon U–Pb dating shows that the Yuqikapa pluton was emplaced in the Anisian (~243Ma) and the Muztaga and Taer plutons that contain microgranular enclaves were emplaced in the Ladinian (234–227Ma). The Yuqikapa pluton is composed of peraluminous high-K calc-alkaline two-mica granites (monzogranite–syenogranite–alkali-feldspar granite), with initial 87Sr/86Sr ratios of 0.7071–0.7077, ε Nd (T) of −4.4 to −6.3 and ε Hf (T) (in-situ zircon) of −3.3. Elemental and isotopic data suggest that they were formed by “wet” anatexis of the Precambrian metasedimentary and metaigneous rocks in the continental collision (overthrust) zone. The Muztaga and Taer plutons consist of metaluminous to weakly peraluminous high-K calc-alkaline granitoids (granodiorite–monzogranite), with initial 87Sr/86Sr ratios of 0.7052−0.7104, ε Nd (T) of −3.6 to −7.3 and ε Hf (T) (in-situ zircon) of −3.1 to −1.0. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metasedimentary and metaigneous rocks in the normal lower-crust (<40km) for the Muztaga pluton and in the thickened lower-crust (~40–50km) for the Taer pluton, triggered by underplating of coeval (233–226Ma) mantle-derived enclave-forming magmas. The enclaves are basic (SiO2 48.0–51.6wt.%) to intermediate (SiO2 53.0–54.6wt.%) with high K2O (1.4–4.2wt.%). They generally have lower initial 87Sr/86Sr ratios (0.7034–0.7084) and high initial ε Hf (−1.1 to +1.2) than their respective host granitoids. The enclave magmas are considered to have been derived from the partial melting of subduction-modified mantle in the spinel stability field (<60km) (enclaves in the Muztaga pluton) and the spinel-garnet transition zone (~60–80km) (enclaves in the Taer pluton). Final closure of the Paleo-Tethys occurred in the Middle Triassic Anisian (~243Ma). The Middle Triassic Ladinian (234–227Ma) dates the post-collisional regime caused by Paleo-Tethyan oceanic slab break-off. [Copyright &y& Elsevier]

Abstract: This paper presents detailed SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotope geochemistry of three intrusive plagiogranite bodies formed in an island arc setting within the Oytag ophiolite suite of the Oytag–Kuda Suture Zone. SHRIMP zircon U–Pb dating of two of these intrusions shows that they were emplaced into the Oytag volcanic rocks at 337.5±4.1 Ma and 327.7±4.9 Ma, and that the younger intrusion contains inherited zircons ranging from 435.3 to 480.8 Ma. Both intrusions are composed of low-Al trondhjemite and tonalite. The rocks have low K2O and Sr and high Y contents with low Sr/Y ratios. They have relatively low rare earth element (REE) concentrations and are depleted in light REE (LREE) and relatively enriched in heavy REE (HREE), with marked negative Eu anomalies in the chondrite-normalized REE patterns. They have initial 87Sr/86Sr ratios of 0.7048 to 0.7068 and ε Nd (T) values of 6.2 to 7.6, which are lower than those of typical MORB. In situ Hf isotopic compositions of zircons with Early Carboniferous age from both intrusions are characterized by positive initial ε Hf values, ranging from +12.5 to +19.5, similar to typical MORB. The inherited Ordovician zircons in the younger intrusion have initial ε Hf values of −1.9 to +3.1, similar to zircons from Ordovician granitoids in the region. Detailed elemental and isotopic data suggest that the Oytag plagiogranites were formed in an oceanic island arc setting, by differentiation of arc tholeiitic magmas that formed in response to the intra-oceanic subduction. The inherited zircons are interpreted as the xenocrysts captured from the incipient oceanic crust that contains relicts of discrete fragments of continental crust with Ordovician zircons, through which the plagiogranite was emplaced. The Oytag ophiolite suite might be the remnants of an ancient island arc, the basement of which was the incipient oceanic crust. The Oytag–Kuda Suture Zone is suggested to be a multiple suture zone that represents the remnants of both the Proto-Tethyan and Paleo-Tethyan oceans. The western Kunlun orogen was therefore not a long-lived active continental margin during the early and late Paleozoic times. It most likely underwent at least two orogenic cycles and thus might represent a multiple orogenic belt. [Copyright &y& Elsevier]

Highlights: [•] First reported Neoproterzoic (∼740Ma) igneous rock in Chinese Central Tianshan. [•] The granite is an A1-type granite developed in a rift-like environment. [•] Central Tianshan recorded Neoproterozoic rift-related igneous events related to the breakup of Rodinia. [ABSTRACT FROM AUTHOR]