The geological significance of a Paleozoic mafic granulite found in the Yiyang area of northeastern Jiangxi Province

Abstract

A mafic granulite has been found in southern Yiyang county in northeastern Jiangxi Province. This granulite has a mineral assemblage of garnet+plagioclase+hypersthene+biotite+magnetite. Based on the composition variation of minerals and relationships among them, pre-peak metamorphism (M1) and peak metamorphism (M2) are recognized. A petrogenetic grid and geothermobarometry measurements yield pre-peak metamorphic conditions of 830-870℃ and ~1.0 GPa, and peak metamorphic conditions of 850-900℃ and 0.7-0.8 GPa, suggesting a near isothermal decompression clockwise PTt path. LA ICPMS zircon U-Pb dating indicates that granulite facies metamorphism occurred about 436 Ma, and its protolith was possibly formed in the early Neoproterozoic. Coupled with available data, we suggest that early Paleozoic (Caledonian) high-grade metamorphism in the Cathaysia Block is related to collisional orogeny, which probably results from the collision-compression between the Yangtze Block and Eastern Gondwana.