Geochronology and geochemistry of the Yazidaban ophiolitic mélange in the Qimantagh: Constrain on the Early Paleozoic back-arc basin of the East Kunlun Orogen, northern Tibetan Plateau

The East Kunlun Orogenic Belt in the northern Tibetan Plateau can be divided into, from north to south, the Northern, Central and Southern Kunlun Belts by the Qimantagh–Xiangride, Aqikekulehu–Kunzhong and Muztagh–Buqingshan sutures. The Yazidaban ophiolitic mélange, located in the westernmost of Qimantagh–Xiangride suture between the Northern and Central Kunlun Belts, consists predominantly of serpentinite, basalt, diabase and andesite. The serpentinites are characterized by low ΣREE contents and depletion of mid-REE showing an ophiolitic ultramafic affinity. The basalts display low ΣREE contents, slightly enrichment of LREE, depletion of LILE and insignificant fractionation of HFSE, which are attributed to E–MORB. Both diabases and andesites are characterized by high ΣREE, strong enrichment of LREE, depletion of Nb, Ta, P and Ti, and significant fractionation of HFSE. These geochemical characteristics indicate that the diabases and andesites were mostly generated in a subduction-related setting. Igneous zircons from the diabase yielded a ²⁰⁶Pb/²³⁸U age of 421.5 ± 2.2 Ma (MSWD=0.44), representing the formation time of subduction-related rocks. Together with regional geology, all 27 above constraints on the ultramafic rocks, basalts, andesites and diabases suggest that the Yazidaban ophiolitic mélange represents the remnants of oceanic crust of a back-arc basin and associated subduction-related magmatic rocks.