PETROLOGY OF THE KAMSTE OPHIOLITE MÉLANGE FROM EAST JUNGGAR, XINJIANG, NW CHINA

Abstract

A newly discovered ophiolite outcrop in Kamste region, locating in the west part of the Kelameili ophiolite belt in east Junggar, consists of basalt, metagabbro, pyroxenite, serpentite schists, siltstone, and volcanic breccia. No exsolution texture occurs in pyroxene in the pyroxenite samples, which implies that the mantle rocks gradually exhumated at least in the upper mantle. Three kinds of amphiboles were identified in pyroxenite: amphibole with exsolution of Cr-magnetite lamellae (Amp I, Mg-Hastingsite), homogeneous amphibole coexisting with Amp I (Amp II, Mg-Hastingsite hornblende), and amphibole replaced clinopyroxene margins (Amp III, Tschmakite Hornblende). Based on the characteristics of the studied amphibole, we suggest that the mantle rocks were elevated to shallow levels (probably at the lower crust), which caused the decomposition of amphibole and formed the exsolution texture. When the ophiolite mélange was elevated to the middle crust level, these rocks undergone retrograde metamorphism at amphibolite phase. Afterwards, these rocks have undergone retrograde metamorphism at greenschist phase when they reached the shallow level of the continental crust.