Ocean-Continent Subduction within the Paleotethyan Archiopeligic Ocean from Mineralogical Evidence of Muztag Ophiolite, Eastern Kunlun Mountain, China

摘要

Former studies show that the Muztag ophiolite, outcropped in the East Kunlun area of Xinjiang, formed in a supra-subduction zone environment. This study is to gain more information about the type of subduction zone. Through field work, thin section observation and microprobe analysis, petrological and mineralogical characteristics of the metamorphic peridotites of this ophiolite are obtained. Although the olivines of metamorphic peridotites appear in three textures of metamorphic relict, metamorphic recrystallizations and orthopyroxene-melting crystallizations by thin-section observations, they have stable and low Fo range of 87.8-89.5 by microprobe analysis. The orthopyroxenes show metamorphic relict and melting relict textures, with a low En of 88-90 and a wide range of Al2O3 content, from 2.90 wt% to 5.13 wt%. The spinels develop anhedral-subhedral textures, with Cr#（=Cr/（Cr+Al）） focusing on two ranges of 0.508-0.723 and 0.100-0.118, respectively. Based on these petrological and mineralogical observations, and combined with the era and tectonic setting for the Muztag ophiolite, it can be concluded that the ophiolite formed in a supra-subduction zone where the oceanic crust subducted down to the continental arc with a thick continental crust, and resulted from ocean-continent subduction within the Paleotethyan archiopelagic ocean in the East Kunlun area of Xinjiang.