东天山苦水变质地带变质作用特征及其成因研究

CHARACTERISTICS AND ORIGIN OF THE KUSHUI METAMORPHIC BELT IN THE EAXTERN TIANSHAN MOUNTAINS

The Kushui metamorphic belt is located at the eastern part of Tu-Ha basin.It consists of schistose epimetamorphic rocks,phyllite,schist,granulite and amphibolite.Metamorphism is largely of a medium-pressure-facies series with assem- blages that include kyanite,staurolite and sillimanite.The study of chemical characteristics of metamorphic rocks displays that most metamorphic rocks are derived from volcanic protoliths;others are from sedimentary protoliths.The compositions of the main rock-forming minerals such as muscovite,hornblende,garnet and staurolite indicate that the Kushui metamorphic belt underwent hormblende-facies metamorphism.A whole rock, Rb-Sr,isochron age of 219.8 Ma implies that the metamorphism occured at the end of the Carboniferous period.The origin of metamorphism is controlled by the activities of faults, At the end of this paper we conclude that although the strata of the Kushui metamorphic belt were deposited in an extensional setting,the medium-pressure type regional metamorphism is related to post-extension compressional tectonism.