摘要
High-pressure ( HP) mafic granulite is characterized by the key assemblage garnet-clinopyroxene-plagioclase-quartz,and it is one of the best carriers to studyoceanic or continental crust subduction-collision. The HP mafic granulite occurs as the tectonic block in the Early Paleozoic sedimentary strata of the northern Lhasa terrane. The protolith of the HP granulite is a gabbro,which experienced four-stage metamorphism: early amphibolite-facies ( 0. 9～1. 0GPa,710～720℃ ) ,the peak HP granulite-facies ( 1. 55～1. 65 GPa,730～740℃ ) ,granulite-facies (～0. 82GPa,～821℃ ) and later amphibolite-facies ( 0. 60～0. 68GPa,520～540℃ ) , respectively. The clockwise metamorphic P-T path includes an early prograde process of isobaric decreasing temperature and subsequent isothermal distinctly increasing pressure,and a retrograde process with early slightly heating and decompression and subsequent late decreasing of temperature and pressure,indicating that the HP mafic granulite formed in the high geothermal gradient and experienced heating retrograde process. Therefore,the formation of HP mafic granulite may not be related to the typical oceanic subduction,rather mid-ocean ridge subduction and mantle plume are possible control factors in its genesis.