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As relics of oceanic lithosphere, ophiolites exposed in the East Kunlun region are crucial for deciphering the evolution from the Proto-Tethys to the Paleo-Tethys. Two ophiolite belts have been recognized in the East Kunlun Orogenic Belt: the northern Heishan-Dagele-Qingshuiquan Ophiolite Belt and the southern Muzitag-A'nyemaqen Ophiolite Belt. Most basaltic rocks in the northern ophiolite belt show apparent geochemical features of enriched mid-ocean ridge basalts, with some of suprasubduction zone-type affinity, and probably formed in arc to back-arc settings with ages of 537–406 Ma. Cumulates (wehrlites) and arc-related volcanics in these ophiolite complexes also display a subduction-related signature. However, most basalts in the southern ophiolite belt exhibit characteristics of mid-ocean ridge basalts and plume-related basalts, which are unrelated to subduction zone. The anhydrous troctolite outcrops in the southern belt also support this viewpoint. Statistics of all the available age data for the southern ophiolites indicate two cycles of seafloor spreading or plume activity, which gave rise to two main epochs of magmatic activity at 535–450 Ma and 345–308 Ma, respectively. The northern ophiolite belt recorded the evolution of the Proto-Tethys Ocean from at least the Early Cambrian to the Late Silurian. Based on geochronological and geochemical comparisons, the southern ophiolite belt shows similarities with the ophiolites in the Longmucuo-Shuanghu suture of Qiangtang on the south, which record the closure of Proto-Tethys Ocean and the opening of the Paleo-Tethys Ocean. The spatial and temporal distribution of the two ophiolite belts in the East Kunlun Orogenic Belt reveals the long-lived evolution from the Proto-Tethys to Paleo-Tethys system. [ABSTRACT FROM AUTHOR]

Whether or not the Altyn Tagh terranes in northwest China were part of the Rodinia supercontinent is unclear due to the apparent absence of rift-related igneous rocks. We present U-Pb geochronology, mineral chemistry, whole-rock major and trace element and Sr-Nd isotope data for the Yapuqiasayi mafic dykes in the North Altyn Tagh. Zircon and baddeleyite from a mafic dyke sample yield indistinguishable U-Pb results and a weighted mean 207Pb/206Pb date of 740 ± 11 Ma, interpreted as the igneous crystallization age. The dykes are tholeiitic in composition, with high TiO2, Zr/Sm and Zr/Y, resembling intraplate basalts. Whole-rock major and trace elements, together with Sr and Nd isotope data, indicate that the dyke magmas originated by 3–5% partial melting of a garnet-poor (<1%) asthenospheric mantle source and were variably modified by crustal contamination. These features, together with mineral chemistry and field observations, indicate that these mafic dykes formed in a continental rift setting, possibly induced above a mantle plume. We show that the Yapuqiasayi dykes are similar in age and petrogenetic characteristics to mafic igneous rocks in Australia, South China, Seychelles, Laurentia, and Tarim, and speculate that their emplacement in North Altyn Tagh was associated with rifting and break-up of the Rodinia supercontinent above a Neoproterozoic superplume. [ABSTRACT FROM AUTHOR]