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

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.