Southwestern Tianshan HP-UHP metamorphic belt developed subduction-zone metamorphic rocks affected by large-scale fluid flows,its veins and host rocks provide important informations about the infiltrating fluid in subduction zone.Based on the previous bulk-rock geochemical studies on metamorphic rocks developed veins in the subduction zone,We have conducted an in situ element study of glaucophane,garnet,omphacite,phengite and other minerals in the veins and host rocks of the metamorphic rock samples to compare the compositional differences of the same mineral in veins and host rocks.This study aims to deeply understand the differences of bulk rock compositions between veins and host rocks,and the geochemical behaviors of related elements in the fluid-rock interaction and fluid properties in subduction zones.According to the petrological characteristics,the samples can be divided into glaucophane-rich veins,epidote and carbonate-rich transitional part and the omphacite-rich interiors.The calculation of element budgets reveal that the relationship between the difference of bulk-rock compositions and host minerals and their abundances.The higher contents of medium-heavy rare earth element(M-HREE)in veins reflects the occurrence of M-HREE by more garnets in veins;and the higher contents of rare earth elements-Th-U-Pb-Sr in the transitional part reflects a large number of epidote group minerals and carbonates controlthese elements;the higher contents of K-Rb-Ba-Cs in omphacite-rich interiors reflects the control of these elements by phengite.On the other hand,the compositional differences of the same mineral in different parts of the rock samples can reflect the geochemical changes of elements in different metamorphic stages and different rehydration degrees directly.Compared with the omphacite-rich interior representing the least fluidinfiltration,the rehydration of external fluid decreased the abundances of phengite and omphacite in the veins and transitional part,and enriched K-Rb-Ba-Cs-Pb-Sr;increased abundance of garnet butdepleted HREE;increased abundance of epidote but depleted in Th-U-light rare earth elements(LREE).Combined with the large amount of carbonates in transitional part,it is speculated that the external fluid is carbonate-bearing serpentinite-derived fluid.After the fluid-rock interaction,the contents of LILE increased and the carbonate component of the fluid decreased significantly in fluid,but the contents of other elements show less variation.
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