大洋俯冲带多期变质流体演化：以西天山超高压变质带绿帘石研究为例

The UHP metamorphic belt of western Tianshan is the largest UHP metamorphic belt terrane currently around the world that the oceanic crust experienced deep subduction. There are abundant of HP-UHP rocks and HP veins in this UHP metamorphic belt and the fluid is active. It provides an important natural laboratory for us to study the evolution of metamorphic fluids in the oceanic subduction zone. In this study, we will study the multi-stage epidotes developed in different stages of HP-UHP rocks (eclogite, blueschist, garnet-amphibolite, garnet-muscovite-schist) and various HP veins in Habutengsu and Kebuerte of southwest Tianshan. The in situ Sr-Nd isotopic, in situ trace elements analysis and fluid inclusions analysis, combined with the petrology, whole-rock chemistry and mineral chemistryanalysis, will be carried out to study the the formation temperature and pressure, the characteristics of main and trace element compositions and the variation of Sr-Nd isotopic of the multi-stage epidotes. We will confirm the composition, origin, mechanism, transport scale and geochemical behavior of the multi-stage fluids in the UHP metamorphic belt of western Tianshan. This study will provide insights into the fluid evolution history of the HP-UHP rocks during the subduction and exhumation of an oceanic crust.

西天山高压-超高压变质带是目前世界上最大的洋壳岩石经历深俯冲的超高压变质地体，其流体活动丰富，发育了各种类型的高压-超高压岩石和高压脉体，是研究大洋俯冲带变质流体演化的天然实验室。本研究拟以西南天山哈布腾苏和科布尔特地区的高压-超高压岩石（榴辉岩、蓝片岩、石榴角闪岩、石榴白云母片岩）和各类高压脉体中不同阶段发育的多期次绿帘石为研究对象，以激光原位微区Sr－Nd同位素和微量元素分析及流体包裹体研究为主要手段，结合细致的岩石学研究、全岩化学和矿物化学分析，考察不同变质期次绿帘石的形成温压条件、主微量元素成分特征及Sr－Nd同位素组成和变化规律，确定西天山高压-超高压岩石及其脉体中多期次流体的成分、源区、成因机制、运移尺度和地球化学行为，构建大洋深俯冲－折返过程中高压-超高压岩石的流体演化历史。

本项目对新疆西南天山变质带各类高压-超高压变质岩及其脉体开展了深入的研究工作。在岩石学研究的基础上，重点对绿帘石和磷灰石开展了激光原位微区Sr－Nd同位素和微量元素分析，并对各类岩石中的绿帘石、磷灰石、石英、榍石、石榴石、绿辉石、白云石等矿物进行了激光拉曼流体包裹体研究，发现了大量的富甲烷和富二氧化碳流体包裹体，确定了西天山高压-超高压岩石及其脉体中多期次流体的成分、源区、成因机制、运移尺度和地球化学行为，构建了大洋深俯冲－折返过程中高压-超高压岩石的P-T-t-fO2-fluid演化历史。