Tectonic evolution of the Meso-Tethyan Ocean: An example from the Nyima region in Xizang

The occurrence of the Middle-Late Jurassic shallow-marine clastic deposits as the residual sea-basin deposits on the southern flank of the Bangong-Nujiang suture zone shows that the subduction and consumption regimes should be ceased after the Middle Jurassic. The Triassic Quehala Group on the southern flank of the suture zone as the abyssal-bathyal deposits is believed to be the passive continental margin deposits and represents the earlier deposits following the formation of the suture zone. The Middle Jurassic calc-alkaline island-arc volcanic rock series unconformably overlain upon the Group are considered as the lag arc volcanic rocks in response to the southward subduction of the suture zone during the Early Jurassic. The 100-km long granite belt within the extent of 80 to 100 km on the southern flank of the suture zone is interpreted as the post-collisional products formed in response to the southward collision of the suture zone during the Middle-Late Jurassic. It is postulated that the Meso-Tethyan Ocean in the Nyima region, Xizang was opened during the Triassic, and enclosed by collision before the Jurassic. The Meso-Tethyan Ocean is an archipelagic ocean composed of many isolated oceanic basins of different geological ages. The mechanisms of arc-arc collision and arc-continent collision and mountain building (continent building) may be interpreted as the ideal models for the interpretation of the tectonic evolution of the Meso-Tethyan Ocean.