Geologic relationships and geochronology of the Cenozoic volcanoes and interbedded weathered mantles of Yulinshan in Qiangtang, North Tibet

The Yulinshan accumulations of volcanic rocks and interbedded weathered man tles provide a unique chance for studying the processes and environment of the formation of the planation surface in central Tibetan Plateau. Geochemi cal, Ar-40/Ar-39 and K/Ar geochronologic investigations of the weathered ma ntles and high-potassium volcanic rocks reveal that the volcano-weathered m antle accumulations formed under arid or semi-arid subtropic environment in 30-24 Ma. The sole planation surface of the Qiangtang region finally forme d in about 20 Ma.