PLANATION SURFACES, PALEOKARST AND UPLIFT OF XIZANG (TIBET) PLATEAU

The elevation of embryonic Xizang Plateau is reconstructed by the rese arch on planation surfaces to be 500-1500 m a.s.l. The formation age o f main surface of 19-7 Ma is determined by 20 fission track data of re crystalline calcite. The modern Xizang Plateau, which has undergone th ree uplifts and two planations since the collision of India and Asia, rose abruptly in 5 Ma B. P. The plateau rose to ''the first critical e levation'' of 1500 m in Early Pleistocene. An intense tectonic movemen t in 0.7 Ma B. P., namely ''Kunya Movement'', made the plateau get ''t he second critical elevation'' of 3000 m.