俄罗斯极地乌拉尔石榴橄榄岩-榴辉岩成因矿物学研究

Garnet peridotite-eclogite is an association of high-pressure metamorphic rock occurring in orogenic belts, and it records important information of orogenic belt formation and evolution although it represents only a small share of the orogenic belt substances. According to their tectonic setting , the Garnet peridotite-eclogite in orogenic belts can be divided into two types: one related to oceanic crust subduction, and other related to continental deep subduction. Consequently, identification of forming environment and protoliths of the garnet peridotite-eclogite has an important significance for reconstruction evolution of orogen. This research will focus on the garnet peridotite-eclogite from the Mica Mountains in south part of Marun-Keu Complex, Polar Urals, Russia. Base on the idea that minerals record petrogenesis information, the garnet peridotite eclogite will be studied on their genesis of major, minor and accessory minerals , involving structure, growing generation, inclusions, major, trace elements and isotopic compositions of minerals. Combined with geochemistry and geochronology of these rocks, we will determine P-T condition of garnet peridotite-eclogite, timing of eclogitic-facies metamorphism and protolith, reconstruct formation and evolution of garnet peridotite-eclogite. This research will provide new and important petrological and mineralogical evidence for understanding evolution of the Polar Urals orogen.

石榴橄榄岩-榴辉岩是一种出现在造山带中的高压变质岩石组合，虽然在造山带物质中所占比例很小，却记录了造山带形成和演化的重要信息。造山带石榴橄榄岩-榴辉岩可分为两种类型，一种与洋壳俯冲有关，另一种与大陆深俯冲作用有关。因此，其成因研究对认识造山带的构造演化具有重要意义。本项目选择俄罗斯极地乌拉尔Marun-Keu杂岩南端云母山的石榴橄榄岩-榴辉岩为主要研究对象，根据岩石成因就是矿物成因的指导思想，对石榴橄榄岩-榴辉岩中的主要矿物、次要矿物和副矿物进行成因矿物学研究，分析各矿物的结构构造、生长世代、矿物包裹体、主微量元素及同位素组成等，并结合岩石地球化学和同位素年代学资料，查明石榴橄榄岩-榴辉岩形成的温压条件、变质时代和原岩时代及其原岩性质，探讨石榴橄榄岩-榴辉岩的形成过程，为深入认识极地乌拉尔造山带的形成演化提供新的重要的岩石矿物学证据。

本项目对俄罗斯极地乌拉尔Marun-Keu杂岩南端云母山的石榴橄榄岩-榴辉岩进行了野外调查，并开展了成因矿物学、岩石学、地球化学和年代学研究。查明了石榴橄榄岩-榴辉岩中的变质矿物为石榴子石、绿辉石、顽辉石、多硅白云母、蓝晶石、韭闪石、镁钙绿闪石、黝帘石和石英; 残留的岩浆矿物为橄榄石(Fo=82-86)、顽辉石( En=79-84)、透辉石和普通辉石。榴辉岩的εNd（t）值为-3~+2，原岩为侵入到东欧大陆边缘的堆晶岩（橄榄岩-辉石岩-橄长岩-辉长岩），原岩时代为520-500Ma， 变质时代为370-360Ma，峰期变质条件为P=18kbar-21kbar，T=740℃-866℃。石榴橄榄岩-榴辉岩和围岩片麻岩为“原地”关系， 代表了俯冲变质的陆壳，而不是洋壳（蛇绿岩），这对认识极地乌拉尔的构造演化极其重要。同时，由于岩石中保留了大量的“火成结构”，对原岩恢复和认识俯冲带矿物相转变过程及其记录的造山带演化也具有重要意义。