K-Ar age of the Cenozoic volcanic rocks in the Nangqen Basin, Qinghai Province and its geological significance

The Nangqen Basin is one of the typical shearing-extensional basins situate d in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been reported in the note. The apparent ages of whole rock and separated biotite range f rom 32.04 to 36.50 Ma. The Ar-40-K (%) correlation isochronal line shows th at there existed neither argon excessing, or radiogenetic argon loosing, i. e. the age represents the true diagenetic time. Volcanic activity in this a rea occurred in the post-collision environment and is controlled by lithosp here substantial thickening and violent intercontinental shearing-strike sl ip faults. There is age difference of the magmatic activity in the east, th e west and the north Tibet. The multi-periodic eruption-intrusion of the ma gmatic melt since Cenozoic is a tracer showing the pulsating uplift of the Tibetan Plateau.