Metamorphic P-T Path Of High-pressure Mafic Granulites (Retrograded Eclogites)from The Dinggye Of Southern Tibet And Its Tectonic Implications

Dinggye is located in the central part of the Greater Himalayan Crystalline Complex(GHC)in southern Tibet.Investigating the metamorphic P-T path of granulite in this area is essential to understand the collision and uplifting process of the Tibetan plateau.The petrological study of the high-pressure mafic granulites(retrograded eclogites)from the region indicates four stages:(1)peak eclogite facies mineral assemblage(M1)consists of garnet(core)+omphacite(psedomorph)+quartz+rutile;(2)high-pressure granulite faciesmineral assemblage(M2)comprisesgarnet(mantle)+clinopyroxene+ plagioclase + ilmenite + amphibole +biotite;(3)medium-pressure granulite facies assemblage(M3)is composed of garnet(rim)+ orthopyroxene + plagioclase + biotite;(4)amphibolite facies mineral assemblage(M4)consists of amphibole+plagioclase.Using theTHERMOCALC program,the thermodynamic modeling in the NCFMASHTO system has been undertaken for the high-pressure mafic granulite.Combined with the conventional thermobarometers and the average P-T estimates,the P-T conditions of the different metamorphic stages are estimated to be 786-826 ?/0.78-0.96 GPa(M2),798-850 ?/0.71-0.75 GPa(M3),and 610-666 ?/0.51-0.60 GPa(M4),respectively,indicating a post-peak clockwise P-T path characterized by nearly isothermal decompression.Combined with available geological data,we propose that the high-pressure mafic granulites(retrograded eclogites)of the Dinggye formed during the Himalayan collisional orogeny,and underwent a post-peak tectonic uplift process of nearly isothermal decompression.