Ocean-Continent Subduction within the Paleotethyan Archiopeligic Ocean from Muztag Ophiolite

The former studies show that the Muztag ophiolite outcropped in the East Kunlun area of Xinjiang Uygur Autonomous Region formed in the supra-subduction zone environment. The petrological and mineralogical characteristics of metamorphic peridotites of this ophiolite are analyzed in order to further study the type of the subducuion zone. Thin-section observations show that the olivines of metamorphic peridotites exist in three textures: metamorphic relict, metamorphic recrystallizition and orthopyroxene-melting crystallizations. Microprobe analyses show that they have stable and low Fo range of 87.8-89.5. The orthopyroxenes show metamorphic relict and melting relict textures, with low En of 88-90 and a wide range of Al₂O₃ content of 2.90%-5.13%. The spinels develop xenomorphic-semi-automorphic textures, with Cr^# (=Cr/ (Cr+Al)) mainly distributing in two ranges of 0.508-0.723 and 0.100-0.118, respectively. Based on the petrological and mineralogical evidences together with the era and tectonic setting of the Muztag ophiolite, it can be concluded that the ophiolite formed in the supra-subduction zone where the oceanic crust subducted down to the continental arc with thick continental crust, and resulted from ocean-to-continent subduction within the Paleotethyan archiopelagic ocean in the East Kunlun area of Xinjiang Uygur Autonomous Region.