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The East Kunlun Orogenic Belt (E-KOB) documents successive subduction and accretion processes of the Paleo-Tethyan Ocean. However, the tectonic regime of the E-KOB at the late orogenic stage remains ambiguous. This study presents new results of whole-rock geochemistry and zircon U-Pb-Hf isotopes of the Xidatan pluton in the southern E-KOB. Detailed investigation reveals that the pluton is composed of quartz monzodiorite, host monzogranite, and igneous microgranular enclaves (IMEs). Zircon U-Pb dating results suggest that they are coeval magmatic rocks emplaced at ca. 206–203 Ma. Geochemical studies reveal that the quartz monzodiorite and IMEs share a common magma source, evidenced by consistent compositions of major elements, congruently enriched LREEs and LILEs, and consistently moderately depleted HFSEs and HREEs. Enriched to slightly juvenile zircon Hf isotopes (εHf(t) = −4.24 to +0.49) indicate that the primitive magmas of the quartz monzodiorite and IMEs involve the addition of mantle-derived magmas. The quartz monzodiorite and IMEs have identical ages, and consistent isotope features with the host monzogranite, together with the observation of ingestion of xenocrysts from host felsic rocks into the IMEs indicating that they were produced through the mixing of the mantle-derived mafic magmas and host felsic magmas. In contrast, The host monzogranite has moderately high SiO2 and Na2O+K2O, but low Fe2O3T and MgO contents. It shows crust-like trace element patterns such as strong enrichments in LREEs and LILEs, but remarkable depletions in HREEs. Along with enriched zircon Hf isotopes (εHf(t) = −3.51 to −0.25), the host monzogranite was most likely to have originated from partial melting of lower crustal mafic rocks induced by underplated mantle-derived magmas. Considering abundant Late Triassic igneous rocks across the E-KOB, these new data provide further evidence that the Late Triassic magmatism in the E-KOB may be related to the delamination of thickened orogenic root under an extensional setting. [ABSTRACT FROM AUTHOR]

The East Kunlun Orogenic Belt (E‐KOB) of the northern Tibetan Plateau is an accretionary orogenic belt, which has experienced complicated tectonic evolutionary processes of the Proto‐ to Palaeo‐Tethys Ocean. The Muztagh‐Buqingshan‐Anemaqen ophiolitic mélange zone (MBAM) is an accretionary complex related to the northward subduction of the Tethyan Ocean. Numerous intrusions outcropped in MBAM have witnessed the long‐term subduction‐accretionary process and thus site the key to comprehending the tectonic evolution of the E‐KOB, as well as the Tethyan Ocean. In this study, petrological, geochronological, and geochemical studies of the Marzheng diorites in the MBAM were carried out to explore the Early Palaeozoic tectonic evolution of the E‐KOB. Zircon U–Pb dating analysis suggests that the diorites were formed in the Early Ordovician at ca. 470 Ma. Furthermore, the εHf(t) values (5.3–14.1), Mg# values (39.7–51.2), and Nb/Ta (12.8–14.8), Zr/Hf (33.8–44.8), and Lu/Yb (0.15–0.16) ratios are generally close to those of depleted mantle‐derived rocks and the diorites were originated from a depleted asthenosphere mantle source. In addition, these diorites are characterized by enriched light rare earth elements (LREEs) (La and Nd) and depleted high‐field‐strength elements (HFSEs) (Nb, Ta, P, and Ti), similar to the fingerprints of arc‐related gabbroic‐dioritic rocks. This is also consistent with their high H2Omelt (6.0–8.3%) and oxygen fugacity (logfO2 = −14.3 to −13.5) features, indicating that they were formed in a subduction‐related setting. Our new investigations suggest that the Proto‐Tethys Ocean in the East Kunlun was still actively subducting northward during the Early Ordovician. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two-mica granites in south Kunlun are identified as S-type with ages of 260–257 Ma. • These S-type granites were derived by H 2 O-fluxed biotite melting of metagreywacke. • These S-type granites and their genesis indicate anatexis of an accretionary wedge. S-type granites are striking products of supracrustal reworking and can provide crucial constraints on the anatexis of accretionary wedges in an accretionary orogen. In this study, we present new zircon and monazite dating results, whole-rock geochemistry, and zircon Lu-Hf isotopic data for the two-mica granites in the Muztagh area of the South Kunlun Belt. Integrated dating results reveal that the two-mica granites crystallized at 260–257 Ma. These two-mica granites are characterized by the presence of muscovite and an aluminum saturation index of 1.04–1.13 typical for S-type granite affinity. They display enrichment in LREEs and LILEs, depletion in HFSEs, and weak negative to positive Eu anomalies. The high CaO/Na 2 O ratios and Sr contents, and low Rb contents, together with a comparison with experimental melting results suggest that the two-mica granites were derived through H 2 O-fluxed biotite melting of metagreywacke. The ε Hf (t) values for co-magmatic zircons display a wide range from −11.5 to +1.14, together with heterogeneous ε Hf (t) values (−10.1 to +6.72) for inherited cores implying a mixed source involving ancient sediments and juvenile volcanic materials. Accordingly, the protoliths of the two-mica granites were formed in the forearc setting, and the Late Permian two-mica granites were generated in the subduction environment related to the Paleo-Tethyan Ocean. Our results, along with the occurrence of the Early Paleozoic peraluminous granites in the South Kunlun Belt, suggest that the forearc accretionary complex in the E-KOB underwent multiple anatectic events during continuous subduction and accretion of the oceanic plate. [ABSTRACT FROM AUTHOR]

• Wulonggou granulite has experienced 940 Ma granulite facies metamorphism. • A clockwise P-T path was established involving P-T at > 12 kbar and 810–840 °C. • East Kunlun underwent a collisional tectonic setting in early Neoproterozoic times. The P–T path of high-pressure (HP) granulite is a sensitive indicator providing metamorphic evidence on the convergence process and on the evolutionary history of orogenic belts during the supercontinent circles. The Wulonggou mafic granulites in the East Kunlun Orogen are intercalated as lenses/boudins within the dominant amphibolite facies basement rocks. Based on microstructures and mineralogical observations, three mineral assemblage generations can be recognized in the granulite samples: (1) inclusions within garnet and amphibole comprising cpx + pl + amp + qtz + rt; (2) the matrix assemblage grt + cpx + pl + amp + qtz + rt ± bt ± ilm; and (3) a retrogressive assemblage consisting of kfs + pl + qtz + amp coronas around garnet. Phase equilibrium modeling and conventional thermobarometric calculations reveal that the Wulonggou granulite has experienced (1) first HP granulite facies metamorphism at > 12 kbar and 810–840 °C, (2) dominant HP granulite facies stage of 800–860 °C at 10.7–12.3 kbar, as well as (3) a retrograde stage of 620–650 °C and 6.7–8.1 kbar, implying a clockwise P–T path. Zircon U–Pb geochronological results indicate that the mafic granulites and the gneissic country rocks yield similar Neoproterozoic metamorphic ages of 939–941 Ma. The granulite also yields a zircon U–Pb age of 444 ± 7 Ma and amphibole 40Ar/39Ar plateau age of 433 ± 1 Ma, suggesting an Early Paleozoic metamorphic overprint at ca. 440 Ma. Together with our previous studies on the contemporaneous Neoproterozoic magmatism and metamorphism, all the above lines of evidence constrain that the Wulonggou mafic granulite has experienced high pressure granulite facies metamorphism at ca. 940 Ma, suggesting a Neoproterozoic collisional orogeny in the East Kunlun Orogen, which has been overprinted by the Early Palaeozoic orogenic processes. [ABSTRACT FROM AUTHOR]