Late Cenozoic uplift-exhumation history of Qinghe-Fuyun region, Altay, Xinjiang—Evidence from apatite fission track

The Mesozoic and Cenozoic intra-continental orogenic processes of the Altay orogen have been widely studied. However, the late Cenozoic uplift and exhumation history of China's Altay Mountains and the problem as to when the present-day Altay Mountains were shaped remain poorly understood. Based on an apatite fission-track (AFT) analysis of five granite and gneiss samples from the Qinghe-Fuyun region and the investigation of the thermal history, the authors obtained some new information concerning the late Cenozoic uplift-exhumation of China’s Altay Mountains. The AFT ages vary in the range 18.7±1.6~22.7±2.2Ma, and the track length is between 11.6±1.2μm and 13.1±1.4μm. Modeling of the fission track data shows a four-stage thermal history. The first stage is represented by a period of prolonged stability before 28Ma, the second by a Late Oligocene-Early Miocene (28~18Ma) rapid cooling, the third by another stable period from 18 Ma to 8Ma, and the fourth by a rapid cooling after ca.8~6Ma. The last cooling phase (ca.8~6Ma) was characterized by the fast uplift-exhumation in this area, resulting in the present geomorphology of China's Altay Mountains. Things were similar in other orogens of western China. The two stage rapid uplift-exhumation was coeval with the uplift of the Tibetan Plateau, which should be the response to the India-Eurasia collision.