Fig. 4 Time elevation map for southern Tibetan Plateau. Data indicate that 15 Ma ago the basin floor in Namling lay at an altitude of ~4600m, implying that there was only small topographic relief between plateau surface (>5000m) and intramontane basins during the mid Miocene. The elevation differential between the Namling basin and the plateau surface has remained virtually unchanged between 15 Ma ago and 600m today. Pre-Eocene elevation is inferred from structural constraints in southern Tibet11