Late Indosinian mantle-derived magmatism in the East Kunlun

Abstract

A phase of mantle-derived magmatism occurred extensively in the East Kunlun orogenic belt in the late Indosinian period.The typical rock types are hornblende gabbro,lamprophyre,and diabase.The Waitan rock body at Shihuigou is the largest one of the igneous rock bodies in the belt.It has a 40 Ar / 39 Ar age of ～220Ma and shows the distinct features of crystallization differentiation.According to the geologi-cal,petrological,and geochemical characteristics,the magma originated from the upper mantle source area at a depth of 90km.At the presence of abundant volatiles(H 2 O),olivine tended to be more stable dur-ing partial fusion and more pyroxene and spinel components entered the magma ,thus constraining the high-Cr and low-Ni characteristics.The extensive occurrence of the mantle-derived magma is believed to be a response of the asthenosphere-lithosphere system of the area to the closure of the Tethyan Ocean as well as the result of underplating of mantle-derived basaltic magma at the base of the thickened crust.