东喜马拉雅构造结高压基性麻粒岩成因与构造意义OA北大核心CSTPCD

There are typical high-pressure pelitic,felsic,and mafic granulites in the Namche Barwa Complex in the Eastern Himalayan Syntaxis.However,the distribution and spatial variation of metamorphic conditions and timing of the high-pressure granulites in the Namche Barwa complex needs to be further studied.In this paper,we conducted a petrological and geochronological study for high-pressure mafic granulite from the Baga area in the southwest segment of the Namche Barwa Complex.The high-pressure mafic granulite consists of garnet,amphibole,clinopyroxene,plagioclase,biotite,and quartz,and the porphyroblastic garnets show growth compositional zoning.The granulite contains three stages of mineral assemblage:the prograde one is the core of porphyroblastic garnet and hosting mineral inclusions,including garnet,quartz,titanite,and apatite;the peak metamorphic assemblage is the rim of porphyroblastic garnet and matrix minerals of clinopyroxene,plagioclase,amphibole,quartz,rutile,and melt;the retrograde assemblage is symplectitic and matrix minerals,including clinopyroxene,amphibole,plagioclase,biotite,quartz,and titanite.The high-pressure granulite has a clockwise P-T path,with peak metamorphic conditions of 1.5 GPa and 915 ℃ and～26％(volume)partial melt under the peak condition.The retrograde metamorphism and melt crystallization of the granulite is likely to have occurred at～26 Ma,and last until～14 Ma.Combined with previous studies,we suggest that the high-pressure granulites in the Namche Barwa Complex have a wide spatial distribution,extending at least more than 80 km from the northeast Gala,Zhibai,Pai to the southwest Baga area,and that these granulites have similar metamorphic conditions and metamorphic time scale.This study indicates that a large number of high-pressure granulites in the Namche Barwa Complex were derived from high-temperature and high-pressure metamorphism and partial melting of the underthrusted Indian continental crust,representing the thickened lower crust of Himalayan orogen.The voluminous melts produced by intensive partial melting of the high-pressure granulites provide the sources for Himalayan granites.