ABSTRACT
There is a great volcanic belt at the northern Tibetan Plateau. It is one of the famous intracontinental volcanic belt on the Earth. On the basis of forming ages, rock association series, geochemistry and isotopic components this belt is divided into two parts: the Qiangtang sub-belt in the south and the Kunlun sub-belt in the north. They are characterized by special enriching in K2O(K2O>Na2O wt%), REE. In genesis they could be related to an initial rift zone developed in Oligocene-Miocene and an intraplate subduction zone formed in Pleistocene respectively. It is interesting that the Quaternary enriched-K2O lavas show that the higher 87Sr/86Sr(i) (0.7089–0.7105) and 206Pb/204Pb (18.711–18.834),207Pb/204Pb(15.087–15.701), 208Pb/204Pb(38.900–39.1909) but lower 143Nd/144Nd(0.5121–0.5123) than Cenozoic volcanic rocks of the East China. Perhaps these characters suggest that the primary magmas of such lavas might have been derived from partial melting of the EMII type heterogeneous enriched mantle source, but they were contamined by continental crust during rising and eruption. The Tibetan Plateau has involved some important evolutional stages since Cenozoic. The time-space distribution and petro-geochemistry of the Cenozoic magmatisms are closely related to the lithospheric evolution.
