K-Ar Ages of Cenozoic Volcanic Rocks from Gongjue Basin in Eastern Tibet

Based on the isotopic chronologic results of Cenozoic volcanic rocks from Gongjue basin in eastern Tibet, the uplifting of the Tibetan plateau was studied. The K-Ar diluted ages of seven volcanic rocks from the Gongjue basin in eastern Tibet are firstly reported. Apparent ages of the whole rock and their biotite are 40.8 to 46.2 Ma with an average of 44.2 Ma. Radiogenic Ar and K of the samples compose an isochron line with high correlation coefficient, which almost passes through the origin. The result indicates that there is neither residual Ar nor loss of radiogenic Ar in these samples. Therefore, they give the eruption ages of the volcanic rocks (i.e. middle Eocene). The volcanic activities in the studied region occurred in the post-collision tectonic setting of Indian-Eurasia plate collision (about 50 Ma) and were controlled by intra-continental horizontal shear faults. Evidences including the published data show that the Cenozoic volcanic activities in eastern Tibet vary greatly. The variety can be considered as the product of the crust-mantle interaction due to the multi-stage uplift in the (Tibetan) plateau.