The preliminary study of the ophiolitic melanges along the Yarlung Zangbo Grand Canyon, Xizang

Three lithostratigraphic units are recognized along the Yarlung Zangbo Grand Canyon, Xizang: Namjagbarwa Group (Pt₁nj), Daguaiwan Group (Mz) and Gangdise Group (Pt₁gd). The Daguaiwan Group intermediate between the Namjagbarwa Group and Gangdise Group is developed dominantly in the northeastern and southeastern parts of the Yarlung Zangbo Grand Canyon, and consists of metabasalts or diabases, pyroxenites, magnesian peridotites, quartzites and marbles. These rocks show many similarities in rock type and chemical composition to ophiolitic suites but differences in lithochemistry from typical mid-oceanic ridge ophiolites. They are interpreted to form in a moderately to slowly extended small oceanic basin which has the features of the continental crust and may be ascribed to an intercontinental sea or a back-arc basin. The intense folding, uplifting and denudation of the study area since 45 Ma allowed the lower crust to have been subjected to more extensive erosion to form the giant canyon.