Metamorphism Evolution And Geological Significance Of Garnet Pyroxenite In Song Yan Area Of Southwest Zhejiang Province

The Badu Complex is the oldest metamorphic rock in Cathaysia Block,and experienced several episodes of metamorphism.Especially,it is obvious that indosinian metamorphic rework in the southwestern Zhejiang Province.There is a set of mafic metamorphic rock:garnet pyroxenite and garnet amphibolite in the Eight Group of Songyang area,Southwest Zhejiang Province,metamorphism evolution of which is still unclear.Therefore,we present the coherent studies from mafic granulites of the Badu Group,which is composed of“garnet+clinopyroxene+amphibolite+plagioclase”.Through a combined study of petrography,mineral chemistry,geochemistry and metamorphic evolution,we get these following several new findings.The protoliths of mafic granulites of the Badu Group are alkaline basalt,which are experienced the oceanic island magmatism,and are interrelated intraplate and mantle plume.garnet amphibolite was degenerated from garnet pyroxenite rather than eclogite,and has experienced three stages of metamorphic evolution.Peak high-pressure granulite facies stage?M1?consists of garnet+sahlite±ilmenite±quartz.Post-peak near isothermal decompression medium granulite facies stage?M2?is characterized by typical decompression reaction textures and mineral assemblages of orthopyroxene+plagioclase?An=90⁹2?,and amphibolite-facies retrograde metamorphic stage?M3?is characterized by the assemblage of amphibole+plagioclase?An=33⁵3?+ilmenite±sahlite±quartz.Phase equilibria modeling in the system Na₂O-CaO-FeO-MgO-Al₂O₃-SiO₂-TiO₂-H₂O and traditional thermobarometry were applied to obtain P-T conditions of different metamorphic stages.P-T conditions of 11.6¹2.5kbar and 780⁸40?for M1,7.4⁸.2kbar and 800⁸80?for M2,and 6.6⁷.5kbar and 500⁵60?for M3 were obtained.In this study,on the basia of the investigation of petrography and mineral chemistry,it was found that garnet amphibolite was degenerated from garnet pyroxenite rather than eclogite,Its metamorphism evolution confined a typical clockwise P-T path dominated by near isothermal decompression characteristic?ITD?.The clockwise P-T path reveals that the Badu Complex of Cathaysia Block involved in the subduction/collision followed by exhumation and cooling events.the events are related with the amalgamation of the Indochina Block—South China—North China in the paleo-Tethyan domain.