Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Abstract

Coesite occurs in garnets from quartz schists and pelitic schists in the Makbal Complex of Kyrgyzian Tien-Shan. The thick quartz schists interbedded with pelitic schists are the transitional facies after coesite schists. Quartz-pseudomorph after coesite also appears widely in pelitic schists and quartz schists, but is rare in eclogitic rocks. The growth zoning of garnets and Na-Ca amphiboles in eclogites and the garnet-omphacite geothermometry indicate that the metamorphic P-T paths of eclogites are different from each. Ultra-high (UHP) pressure metamorphic rocks of the Makbal Complex are mainly composed of pelitic and quartz schists. All eclogite lenses are included in the host UHPM rocks, although most of them do not contain UHP metamorphic (UHPM) evidences. The K-Ar ages of phengite in a host pelitic schist and of paragonite in an eclogite are approximately 500 Ma, while those of biotite and phengite in a biotite-bearing mica schist and of winchite in a winchite schist are approximately 769-717 Ma and 881 Ma, respectively. The evidence indicates that this complex is a tectonic mélange. These geological relationships suggest that the ascending substances must be pelitic and quartz schists. The UHPM rocks in the ascending material capture many exotic blocks as xenoliths during intrusion into the upper crust.