Apatite fission track constraints on the Neogene tectono-thermal history of Nimu area, southern Gangdese terrane, Tibet Plateau

Apatite fission track dating of five samples from Cenozoic volcanic strata in the Nimu District in the southern Gangdese Terrane exhibits single population grain ages with a single mean age and associated central ages ranging from 6.8 ± 0.6 Ma to 9.7 ± 1.2 Ma. Mean track lengths are between 12.9 ± 1.7 µm and 14.2 ± 2.3 µm with a single peak characteristic of a single thermal event. The newly documented ages coincide well with the age of high sedimentation rates in the North Tibet Basin that resulted from a 9–5 Ma compressional event. Track length modeling allows three stages to be identified in the sample cooling. The first stage (12–8 Ma) records a period of relative stability with little, if any, cooling at temperatures of 120–110°C suggesting this region had low relief. The second stage (8–2 Ma) reflects rapid cooling with temperatures decreasing from ∼110°C to surface temperatures of ∼15°C. This stage can be related to far-field effects of the Himalayan collision, which probably generated the surface uplift and relief that defines the present-day Gangdese Mountains. The mean uplift rate of this period is estimated to be 1.41–0.95 mm/y with total uplift reaching ∼5900 m. The final stage is related to surface evolution since the Pliocene.