Age, geochemical characteristics and tectonic significance of Changshishan ophiolite in central East Kunlun tectonic mélange belt along the east section of East Kunlun Mountains

The ophiolite in central East Kunlun tectonic mélange belt along the east section of East Kunlun Mountains is mainly composed of serpentines, gabbro, diabase, basalt and peat siliceous rock. The LA-ICP-MS zircon U-Pb dating of the gabbro in ophiolite shows that the age is (537.2 ± 3.5) Ma, which indicates that the ophiolite was formed in the Early Cambrian. Detailed petrogeochemical studies show that the protolith of serpentines is peridotite and the rare earth element distribution curve has wide U-type characteristics. The gabbro displays obvious accumulate texture with varying degrees of Eu anomalies. The light rare earth is relatively high but the total rare earth is low. The light rare earth of basalt is relatively higher than heavy rare earth. And it shows systematic enrichment of LILE, no differences of HFSE and slight depletion of Nb and it also has double features of E-MORB and IAB. The ophiolite originated in back-arc basin which had been formed by the subduction of Proto-Tethys Ocean in Buqingshan- Anyemaqen before the Early Cambrian and then eventually formed a basin in East Kunlun region after extension.