THE CHARACTERISTICS OF DEFORMATION AND STRUCTURAL EVOLUTION OF THE COESITE-BEARING ECLOGITES IN SHIMA DISTRICT OF ANHUI PROVINCE, CHINA

摘要

The Shima area of Taihu, Anhui Province, is located in the eastern part of the UHP Dabie belt. The supracrustals, gneissic granites and sporadically small serpentinized ultramafic massifs are exposed. Coesite-bearing eclogites occur as lenses, small intercalations parallel to the regional foliation of the supracrustals and ultramafic bodies. The metamorphic UHP rocks have undergone 6 generations of tectonic deformation which is characterized by the plastic shearing of early stage and brittle fracturing in the later stages. The foliation and lineation of the early stage reflects the crustal contraction regime of the deep leval with plastic shortening and thickening of ductile rheological character. The relict UHP deformation in eclogites, Se foliation and Se lineation, can be deciphered from the wide spread retrogressive amphibolite facies recrystallization. In thin sections cut paralled to L_e normal to S_e, the preferred orientation of (001) cleavage of phengite and c-axis of quartz in the coesite-bearing eclogites are measured by universal stage. The petrofabrics of the UHP eclogites and all of the mesoscopic structures show characteristics of plastic shear flow in UHP stage of metamorphism happened in the dopth of the crust-mantle boundary.