东昆仑榴辉岩成因矿物学研究

Eclogite is a type of high-pressure metamorphic rock which commonly occurs in orogenic belts. Although it represents only a small share of the orogenic belt substances, it records important information on orogenic belt formation and evolution. According to the tectonic settings for the formation, eclogites in orogenic belts can be divided into two types: one related to oceanic crust subduction, and the other related to continental deep subduction. Consequently, eclogites can be an important indicator for recognizing fossil plate boundaries or paleosuture zones. This project selects the newly discovered eclogite in the Eastern Central Kunlun Fault by the proposer as primary research object. Base on the idea that minerals are the recorders for petrogenesis information, with combinations of fieldwork and laboratory work, macroscopic studies and microscopic observations, spot and profile, we mainly do researches on the genesis of main, minor and accessory minerals of the eclogite, make analyses of the structure, growing generation, inclusions, major, trace elements and isotopic composition of minerals. Matched with geochemistry and geochronology of the eclogite and their country rocks, we devote to the confirmations of the forming P-T conditions of the eclogite, the timing of the eclogitic-facies metamorphism and their protolith, and to reconstruct the formation and evolution of the eclogite. Combined with regional geology, we will further discuss the nature and evolution of the Central Kunlun Fault zone, and provide new and important petrological and mineralogical evidence for understanding the evolution of the East Kunlun orogen.

榴辉岩是一种普遍出现在造山带中的高压变质岩，虽然在造山带物质中所占比例很小，却记录有造山带形成和演化的重要信息。按照形成的构造环境，造山带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，榴辉岩成为识别古汇聚板块边界或古缝合带的重要标志之一。本项目选择申请者在昆中断裂带东端新发现的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，采用野外与室内、宏观与微观、点与线相结合的综合手段，对其主要矿物、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，并与榴辉岩及其围岩的岩石地球化学和同位素年代学相结合，查明榴辉岩形成的温压条件、变质时代和原岩性质，恢复榴辉岩的形成演化史。结合区域地质资料，进一步探讨昆中断裂带的性质和演化，为深入认识东昆仑造山带的形成演化提供新的重要的岩石学矿物学证据。

主要对东昆仑东段温泉地区新发现的榴辉岩及其围岩(片麻岩及超镁铁岩) 进行了成因矿物学、岩石学、地球化学和年代学研究，查明了榴辉岩产在片麻岩中，与片麻岩为“原位”关系，可分为粗粒和细粒两种，峰期矿物组合为石榴石+绿辉石+石英±蓝晶石+金红石，多数退变为榴闪岩。榴辉岩原岩为中-基性火成岩，形成时代为934±11Ma，峰期变质时代为428±3 Ma，形成温度为590-650℃，压力大于1.6GPa。副片麻岩原岩形成于大陆边缘环境，形成时代为中-新元古代（Pt2-3），变质时代为430-420Ma。超镁铁岩为形成于岛弧环境的堆晶岩，形成时代为331±2 Ma，属于古特提斯洋壳的残片，与榴辉岩为“构造”接触关系。这些结果不仅表明东昆仑早古生代为陆-陆碰撞型的造山带，而且也限定了东昆仑早古生代花岗岩形成的构造环境，对认识东昆仑造山带的形成演化具有重要意义。