Abstract:

There are tremendous contrasts between eastern and western China in tectonics, magmatism, litho-spheric structure，sedimentary basins and geomorphology. The spatial and temporal distribution of volcanic rocks in the Tibetan Plateau since India-Asia continental collision shows a highly distinctive migration pattern. Initially, igneous activity migrated at ca.45 Ma, around the end of syn-collisional period, away from the Tsangpo collision suture. Between ca. 45 and 6 Ma, volcanic activity migrated outward from the plateau interior, implying wavelike outward propagation of upwelling asthenosphere. A third stage, still in progress, is marked by the migration of activity to northwestern, northeast-eastern, and southeastern peripheral regions of the plateau between 6 Ma and the present. Overall, such a highly distinctive pattern of activity can be interpreted to reflect lateral asthenospheric mantle flow and deep crustal flow induced by the approach, and ensuing collision, of relatively thick (India and Eurasia) continental plates. There seem two deduced channels of mantle flow, that is, one channel eastward to the East China via Lixian-Dangchang along western Qinling Range, and another one southeastward to SE China and Vietnam Cenozoic basalt province via Maquan-Pinbian along the Sanjiang orogenic belt. Volcanic rocks in both LixianDangchang and Maquan-Pinbian show transitional characteristics between the Tibetan potassic volcanic province and the eastern China basalt province. Many geophysical data are also in support of the idea about lateral flow at the asthenospheric and lithospheric levels. To testify this hypothesis, intensive studies along several selected profiles across the transitional region are required for determining the source region and depth at which magmas generated, and revealing the characteristics of the lithosphere and the asthenosphere beneath the two volcanic provinces mentioned above. These studies will no doubt be favorable either for providing igneous constraints on the deduced lateral flow at the asthenospheric and lithospheric levels and the interaction between the above-mentioned two provinces, or for understanding the tectonic relationship between western China and eastern China, which are mainly controlled by the India-Asia collision and by the subduction of the Pacific plate, respectively.

Key words: Tibetan Plateau, potassic volcanic rock, soda volcanic rock, petrogenesis, geodynamics