Numerical Simulation of Thermal Evolution of the Danba Anticline, Sichuan, China

Abstract:

We applied finite difference method with markers in cell technique to simulate the thermal evolution in the Danba anticline, which is located to the north of the Sichuan basin within the Songpan-Ganzi orogen. We obtained the thermal history of the Danba anticline by solving thermokenematic equations for detachment folding. With that, we calculated the corresponding fission track ages based on a chemical kinetic model proposed by Lutz and Omar and compared them with the observed ones to find out the optimal model parameters. Our results show that the Danba anticline is most likely formed by horizontal contraction along a detachment fault at depth about 15 km, corresponding to the brittle-ductile transition in the mid-crust. For the last 25 My, the horizontal shortening is estimated to be about 72 km over a cross section with a width of 180 km. The average contraction velocity of about 2.9 mm/yr but it has been accelerating in a parabolic function to about 5~6 mm/yr at the present time, which is comparable with GPS observations. Our findings suggest that a weak detachement zone should exist beneath the Danba anticline, which might be associated with crustal channel flow.