电子背散射衍射(EBSD)技术在大陆动力学研究中的应用

Electron backscatter diffraction ( EBSD) technique and its application to study of continental dynamics.

电子背散射衍射(Electron backscatter diffraction,简称EBSD)技术可以快捷准确地进行物相鉴定,确定矿物晶体的晶格优选定向和多相岩石中各矿物的空间分布,使其成为定量研究岩石显微构造的理想工具。将岩石组构测量、野外地质观察与矿物的变形实验研究相结合,可以判别物质运动的剪切指向和变形的温压条件,从而进行运动学和动力学机制的分析。本文首先介绍了EBSD技术的原理和主要矿物组构的实验研究进展,然后以国土资源部大陆动力学重点实验室5年来的成果为例,总结了EBSD技术在研究大陆深俯冲和折返的动力学机制和大陆造山带动力学研究中的应用。结果表明:橄榄石和绿辉石的组构揭示了板块深俯冲阶段的组构运动学特征,而石英、斜长石和夕线石的组构可以用来研究地壳内大型韧性剪切带的变形历史,如与苏鲁超高压变质岩折返相关的韧性剪切带、龙门山逆冲剪切带、西昆仑康西瓦走滑剪切带和喜马拉雅造山带的康马拆离剪切带。因此,EBSD技术的应用有助于实现显微构造与宏观构造相结合,建立变质-变形-运动学相统一的地球动力学模型。

The electron backscatter diffraction (EBSD) technique allows us to measure the crystal orientation, determine grain boundary misorientations and discriminate between different materials fast and easily, which make it an ideal tool to quantitatively study microstructure of rocks. Combined with field geological observations and deformation experiments of minerals, the fabric analysis provides important information on shear sense and deformation conditions of rocks, which are critical to study kinematics and dynamics of continents. First, we gave a brief introduction on the EBSD technique and summarized the relationships between characteristic fabrics and deformation conditions of major minerals. Then based on the research projects of the Key Laboratory for Continental Dynamics in the past 5 years, we showed the application of the EBSD technique in studying continental subduction-exhumation processes and the continental orogens. The results indicate that the fabrics of olivine and omphacite were formed during the deep subduction of the Yangtze plate, while the fabrics of quartz, plagioclase and sillimanite can be used to investigate deformation history of large-scale ductile shear zones in the crust, e. g., the ductile shear zones related with exhumation of the Sulu ultrahigh-pressure metamorphic rocks, the Longmenshan thrust shear zone, the Kangxiwar strike-slip shear zone in the western Kunlun Mountains, the Kangina ductile detachment in the Himalayan orogen. Therefore the EBSD technique is very helpful to combine the microstructure with tectonics and construct a continental dynamic model integrated of metamorphism-deformation-kinematics.