西藏冈底斯岩带中段南缘韧性剪切带特征

Basic characteristics of the ductile zone on the southern margin of the central sector of the Gangdise rock belt, Tibet

１∶２０万曲水幅区域地质调查中发现了一条东西向巨大韧性剪切带，据几何形态和显微组构特征，该剪切带属于正剪切带性质，是在始新世晚期（４０～４２Ｍａ）印度板块与欧亚大陆发生碰撞时的产物。区内在构造—岩浆作用下，造成地壳不同层次拆离滑脱及韧性剪切带的形成，解释了地壳增厚、构造变形弱及地球物理多层结构不明显的特征。

An E W trending gigantic ductile shear zone was found during regional geological survey of the 1∶200 000 Qüxü Sheet. According to its geometric form and microfabrics, this shear zone has the nature of a normal shear zone. It is the product of collision of the Indian plate and Eurasian continent during the late Eocene (40～42 Ma B.P.). The tectono magmatism in the study area resulted in the décollement in different levels of the earth's crust and formation of a ductile shear zone. This gives relatively reasonable explanations of crustal thickening, tectonic deformation and geophysically indistinct multi layered structure.