Apatite Fission Track Evidences for Neogene Tectono-Thermal History in Nimu Area, Southern Gangdese Terrane, Tibet Plateau

The apatite fission track for 5 samples were obtained. All samples exhibit that the individual grain ages belong to a single population with a single mean age and have central ages from (6.8±0.6) Ma to (9.7±1.2) Ma. Their mean track lengths range between (12.9±1.7) μm and (14.2±2.3) μm with a single peak. These ages well coincide with high sedimentation rates in the basin of north Tibet and resulted from a final compressional event of 9-5 Ma. Modeling identifies three stages in sample cooling history from about 12 Ma to present day. The first stage records a period of relative stability with little if any cooling taking place during more than about 12-8 Ma at the temperature of 120-110 ℃. The second stage is requirement for rapid cooling from 8 Ma to 4 Ma with temperature from about 110 ℃ to surface about 15 ℃. Final stage belonged to surface evolution since Pliocene. The second stage linked to the far field effects of the Himalayan collision and most likely generated the surface uplift and relief that define the resent-day Gangdese Mountains. The mean uplifting rate was 1.41 mm/a and the uplift reached 5 940 m during the 8-4 Ma.