西天山高压变质岩的流体特征研究

Hydrous high-pressure veins cutting through host blueschists and eclogites in the western Tianshan high-pressure/low-temperature metamorphic belt have been studied. The mineral assemblages of veins are represented by omphacite, epidote/zoisite, garnet, glaucophane, phengite and quartz. Veins could be divided into two kinds, omphacite vein (omphacite >80 mol.%) and omphacite-quartz vein (quartz >50 mol.%)on basis of the modal composition of minerals. The host blueschists and eclogites have meta-N-MORB, E-MORB and OIB-types. The peak eclogite facies metamorphism occurred at 345 Ma, and retrograde greenschist facies metamorphism at 331 Ma. C-axis parallel, non-planar populations of fluid inclusions have been preserved within the omphacites in veins and host eclogites . The microthermometric results indicate that fluids are low-salinity (1-7wt%NaCl) aqueous fluids. The petrographic evidence and thermordynamic calculation indicate that the fluids were released under peak metamorphic conditions (600 °C , 18 - 21 kbar) at blueschist to eclogite transition. The d18O value of omphacite seperates in veins varies from 9.6 ‰ to 10.5 ‰, that of quartz from 12 ‰ to 13.3 ‰, that of whole rocks of veins from 9.77 ‰ to 9.91 ‰. These values are similar to those of whole rocks of host eclogites. The O-isotope data indicate that the fluids have equilibrated with hist rocks on local scale under peak metamorphic temperature (550－600 °C). The fluids were derived from dehydration of host rocks. The d18O value of fluids is about 10.8 ‰. The chemical compositions of major,trace and rare earth elements of veins and related host rocks indicate that Si, Na, Ca, Li, Be, LIL elements (Cs,Rb,Ba), Pb and La-rich, HFS (Nb, Ta, Zr, Hf), REE elements (except La) and Y- depleted fluids were released during subduction of the South Tianshan Oceanic crusts in Paleozoic time. This study is very important for understading the interaction between fluids and crust-mantle.

研究西天山蓝片岩和榴辉岩中的各种脉体及不同尺度上蓝片岩向榴辉岩转变等特征流体现象，流体包裹体，流体序列与变质作用PTt轨迹关系，脉体矿物的稳定同位素特征，流体的来础⑹头拧⒃艘苹坪驮艘乒婺＜傲魈遄饔孟禄С煞值谋浠８醚芯慷蕴教止鸥┏宕畲Ω┏逖罂呛蜕系蒯５南嗷プ饔眉案┏逖罂腔г氐难返染哂兄匾±砺垡庖濉