西藏碧土地区怒江缝合带基本特征与演化

BASIC FEATURES AND EVOLUTION OF THE NUJIANG RIVER SUTURE ZONE IN THE BITU AREA, TIBET

碧土地区怒江缝合带由二叠纪—早三叠世蛇绿混杂岩和志留纪─晚三叠世不同类型沉积岩构成的蛇绿─构造混杂带所组成。带中零星出现的蓝闪石、３Ｔ型多硅白云母等组合表明为中高压变质带，以逆冲断裂、褶皱构造构成的双向背冲叠瓦构造为变形特征。该带经历了６个阶段的演化，最终将冈底斯─念青唐古拉陆块和亲扬子的昌都陆块缝合在一起，形成了现今两弧夹一带之构造格局。

The Nujiang River suture zone in the Bitu area, Tibet, is represented by an ophiolitictectonic mélange zone consisting of PermianPaleogene ophiolitic mélange and different types of SilurianLate Triassic sedimentary rocks. The sporadical occurrence of such mineral assemblages as glaucophane and 3Ttype phengite indicates that this zone is a medium and highpressure metamorphic zone, whose deformation feature is represented by duplex backthrusting imbricate structure formed by thrust faults and folds. The evolution of this zone progressed through six stages, finally resulting in the suturing of the GangsideNyainqêntanglha block and the Qamdo block of Yangtzia affinity and the formation of the present tectonic framework of a zone sandwiched between two arcs.