Cenozoic Yolcanism and Tectonic Evolution on the Tibetan Plateau

Cenowic volcanign on the Tibetan plateau, which shows systematic variations in space and tine, is the volcanic response to the India-A sia continental collision. The volcanign gradually changed from Na-rich+K-rich to potassic-ultrapotassic+adakitic compo sitions along with the India-A sia collision shifting from contact-collisionof 65Ma (i. e,"soft collision") to all-sided collision of 45Ma (i. e,"hard collision". The sodium-rich and potassium-rich lavas with ages of 65~40 Ma distribute mainly in the Lhasa terrane of southern Tibet and subordinately in the Qiangtang terrane of central Tibet. The widespread potassic-ultrapotassic lavas and subordinate adakites were generated from~45 to 26 Ma in the Qiangtang terrane of central Tibet.