欧洲中部波西米亚地块和中国西部柴北缘造山带高压麻粒岩对比研究

Understanding the formation and evolution of high-pressure (HP) granulite in the continental collisional orogen can provide crucial constraints on thegeodynamics of the deeply subducted continental crust and on the tectonothermal evolution of continental collisional orogens. In addition, understanding the HP graniulite-facies and associated anatexis is critical to the formation, fractionation and evolution of continental crust. This project will focus on the comparison of HP granulites and their associated rocks between the Bohemia massif in central Europe and the North Qaidam orogen in western China. The study will be performed on the basis of careful petrographic observation with special attentions to identification of mineral and multiple solid inclusions. Mineral in-situ major-trace elements and radiogenic isotopes as well as mineral stable isotopes will be investigated together with the systematic study of accessary minerals and whole-rock element and isotope analyses. The results will be used to distinguish minerals of different origins in the HP granulites, to trace the early evolutionary history and protolith nature, to understand the relationship between the formation of HP granilite and the continetnal subduction/collision, to provide constraints on thh exhumation mechanism of deeply subducted continetnal crust, and to understand the relationship between HP granulite-facies metamorphism and anatexis and the behaviors of mineral and element in this process, and to further provide insights into the anantectic processes and effects of continental crust.

大陆碰撞造山带中高压麻粒岩的成因和演化对于理解深俯冲陆壳地球动力学以及大陆碰撞带的构造热演化具有重要意义。进一步，理解造山带高压麻粒岩相变质作用及其相关的部分熔融对于大陆地壳的形成、分异、演化具有重要意义。本项目拟对大陆深俯冲/碰撞形成的欧洲中部波西米亚地块和中国西部柴北缘造山带中的高压麻粒岩及其相关岩石进行对比研究，通过系统的岩相学观察、矿物微区元素和同位素分析、矿物氧同位素以及综合的副矿物研究(岩相学、微量元素、U-Pb定年和Hf-O同位素)，结合全岩元素和同位素分析，在区分不同成因矿物的基础上，恢复这些岩石的前期演化历史和原岩性质，查明高压麻粒岩的形成与大陆深俯冲/碰撞之间的关系，进一步制约深俯冲大陆板块的折返机制；查明与高压麻粒岩相变质作用相关的深熔作用的机制和过程并查明该过程中矿物和元素的响应行为，进一步探讨陆壳岩石深部部分熔融过程和效应。

大陆碰撞造山带中高压麻粒岩的成因和演化对于理解深俯冲陆壳地球动力学以及大陆碰撞带的构造演化具有重要意义。理解造山带麻粒岩相变质作用及其相关的深熔作用对于认识大陆地壳的形成、分异和演化具有重要意义。本项目以欧洲波西米亚造山带、中国西部柴北缘造山带和东部桐柏造山带出露的高压麻粒岩及其相关岩石为研究对象，开展了岩相学、全岩元素和同位素、矿物微区主微量元素和同位素、矿物氧同位素以及副矿物锆石和独居石U-Pb定年、微量元素和同位素分析等综合研究。结果恢复了这些高压麻粒岩的形成和演化历史，在此基础上发现碰撞造山带超高温麻粒岩是由大陆地壳俯冲形成高压/超高压岩石后经过加热改造形成的，俯冲板片断离是碰撞造山带中同时发生超高压和超高温变质作用的基本构造机制，而碰撞后张裂造山作用是导致超高温叠加高压/超高压变质作用的主要原因。发现变泥质岩体系中锆石在大陆碰撞过程中不同阶段都可以形成，其溶解和生长受全岩成分影响较小，主要受控于深熔作用的温压条件、熔融程度、转熔反应性质和含Ti矿物的稳定性等。发现并查明了变基性岩中石榴石和锆石在榴辉岩相和麻粒岩相变质过程的组成差异，为正确利用锆石和石榴石准确限定变基性岩的P-T-t轨迹奠定了基础。发现大陆俯冲带深部同时存在硅酸盐熔体和碳酸盐熔体，硅酸盐熔体来自于含水矿物的脱水熔融，而碳酸盐熔体的出现则指示了熔融过程中有碳酸盐矿物参与，因而对于表壳碳进入地幔的循环具有很重要的作用。发现变基性岩和长英质岩石在大陆俯冲带变质过程中具有不同的熔/流体活动行为，发现变基性岩中脉体通常由多期/多来源流体混合形成，无法直接用其组成来限定成脉流体组成。