The discovery and significance of the relicts of ophiolitic mélanges along the Parlung Zangbo in the Bomi region, eastern Xizang

The relicts of ophiolitic mélanges were discovered and mapped, for the first time, during the 1:250000 geological survey along the Parlung Zangbo in the Bomi region, eastern Xizang. These relicts of ophiolitic mélanges as a string of beads are enveloped by granitic intrusives, and consist dominantly of olivine pyroxenite, pyroxenite, gabbro, gabbro diabase, diabase, quartzite, marble and locally banded siliceous rocks. The study of the interrelations between the above mentioned rocks shows that the ophiolites had been subjected to green schist facies metamorphism and deformation prior to the intrusion by the granites. The integration of basin evolution recorded by the sedimentary rocks, Rb Sr ages of the ophiolites, geochemical signatures and ages of the granites on either side of the relicts of ophiolitic mélange zones indicates that the ophiolitic mélanges along the Parlung Zangbo in the Bomi region were formed in the interarc basins during the Carboniferous to Permian. The oceanic crust occurred at least prior to the Late Triassic. The arc arc collision took place prior to the Middle Jurassic due to the northward subduction of the oceanic crust.