The distribution and tectonic significance of peraluminous granites in southern Xizang

The spatio-temporal distribution of the peraluminous granites in southern Xizang are treated on the basis of lithologic zone division, spatial distribution, peak and scale of magmatic activity. The magmatic activity of the peraluminous granites was intiated during the Early Jurassic, and culminated during the middle Miocene, especially from 20 to 10 Ma. The rock types include tourmaline granites, muscovite granites and two-mica granites. The magmatic activity of the peraluminous granites in the Gangdise zone tends to be migrated from the east to the west and from the south to the north. The tectonic evolution of the lithosphere of the Qinghai-Xizang Plateau deducted from the spatio-temporal distribution of the peraluminous granites in southern Xizang may be generalized as:(1) Latest Triassic to Early Jurassic (208-157 Ma), representing an early subduction phase of the Bangong-Nujiang oceanic basin (2) Late Jurassic to Early Cretaceous (157-97 Ma), representing a subduction and collision phase of the Bangong-Nujiang oceanic basin; (3) Late Cretaceous to early Paleocene (97-65 Ma), representing a subduction and initial collision phase of the Yarlung Zangbo oceanic basin; (4) Paleocene to Eocene (65-40 Ma), representing a major collisional stage of the Yarlung Zangbo Oceanic basin and the formation of crust-derived granites, and (5) Oligocene to Recent, representing an intense intracontinental convergence phase.