Mineral Chemistry Of Metapelite And Anatectic Vein Of The Eastern Gangdese Magmatic Arc

The Gangdese magmatic arc,located at the southern Lhasa terrane,was derived from the Mesozoic subduction of Neo-Tethyan oceanic lithosphere and the Cenozoic collision between the Indian and Asian continental plates,representing a natural laboratory of studying the metamorphism and magmatism of subduction and collisional zones.The migmatite and anatectic vein are widely exposed in the eastern Gangdese magmatic arc.Studying the major and trace element composition of minerals from these rocks can provide constraints on the enrichment,distribution and mobility of elements during partial melting.In this master's thesis,a mineral chemical study of the Grt-Ky-two mica schist and associated anatectic vein is presented,and the obtained results are as follows:(1)Grt-Ky-two mica schist has two generations of mineral assemblages.The early assemblage is Gt(core)+ Pl + Bt + Ms + Ilm +Qz + Sil,and the late assemblage is Gt(mantle)+ Pl + Bt + Ms + Ilm + Qz + Ky.The garnet-and plagioclase-rich granitic vein contains garnet,plagioclase,quartz,biotite and muscovite;(2)the garnets from both rocks show an inclusion-rich metamorphic core and an inclusion-poor magmatic rim.The inclusions consist mainly of sillimanite,biotite and quartz;(3)the metamorphic garnet exhibit a growth zoning characterized by gradual increase of Mg O content and gradual decrease of Mn O content from the core to mantle.The metamorphic garnet core displays the rare earth element(REE)patterns with depletion in the light rare earth element(LREE)and enrichment of the heavy rare earth element(HREE).The REE contents are decreases from the inner to outer core.(4)The magmatic garnet rim has lower Mg O contents and Ca O contents in rhythmic variation.The Mn O contents are increased at the outmost rim.The REE contents of magmatic garnet have distinctly rhythmic variation,and the REE pattern is characterized by HREE and MREE enrichment and LREE depletion;(5)Plagioclase from the schist has the zoning with increasing anorthite and decreasing albite contents from the core to rim.The component of plagioclase from the vein is similar to that of the schist,but with no zoning.The plagioclase from both schist and vein has high Eu,La,Pr,Ba,Sr,Y and Sm contents.Biotite and muscovite from both rocks has high Rb,Sr and Ba contents.