Uplift and exhumation of the Chakabeishan ore district in the northern margin of the Qaidam Basin, China: Constraints from fission track thermochronology

The Chakabeishan area is located in the northern margin of the Qaidam Basin, Northwest China, and is an important lithium mining area. However, there is a relatively lower research degree and lack of data constraints of tectonic uplift and exhumation. Using fission track technology, new apatite and zircon fission track results have been reported for the first time in order to reveal the tectonic processes and uplift histories of this area. A total of 11 sample results were obtained, these ages could be divided into four groups, namely, 159-144 Ma, 114-100 Ma, 72 Ma and 52-32 Ma, revealing four periods of tectonic activities. Thermal history modelling provided three episodes of uplift at 120-60 Ma, 60-18 Ma and 18-0 Ma. In the first stage, the Southern Qilian Mountains was reactivated and subducted southward due to collision of the Lhasa and the Qiangtang blocks, resulting in rapid uplift in this area. The second stage is tectonic quiescence period corresponding to a relatively steady uplift. The third stage showing rapid uplift caused by the collision between the Indian and Eurasian Plates. The average uplift rate and total uplift amount of the three stages calculated according to the geological thermal histories are 0.039 km/Myr and 3.27 km, respectively. Using the age-closure temperature method, the exhu-mation rate has been calculated as 0.034-0.148 km/Myr from zircon closure-temperature of 250 degrees C to apatite closure-temperature of 100 degrees C and 0.049-0.076 km/Myr form the apatite closure-temperature of 100 degrees C to 15 degrees C of surface temperature. The exhumation rate is fastest from the Late Cretaceous to Eocene and has then changed a little since the Eocene, with the average exhumation rate of about 0.059 km/Myr. Synthesizing the zircon ages and geological characteristics, this area is characterized by multi-stages mineralization, and the metallogenic age is mainly in the Late Jurassic-Cretaceous.