Two-dimensional finite element modeling on the crustal shortening and the surface erosion-sedimentation process across northern piedmont of the Tianshan Mountains

Abstract

The Tianshan Mountains, located in the northwestern China, are bounded by the Tarim Basin to south and the Junggar Basin to north. In the north piedmont of this mountain range, ongoing thrusting and folding forms a set of roughly parallel anticlines. Geological observations predicted that averaged over last ~1 Ma time scale, the shortening rates of these anticlines are about 2.1–5.5 mm/a; However by averaged over about 10±2 kyr, their shortening rates reduce to merely about 1.25±0.5 mm/a. The slow shortening of the anticlines in the last ~10±2 kyr is coarsely concurrent in time with the last global deglaciation. Here, we use a two-dimensional finite element model to explore crustal deformation across north piedmont of the Tianshan Mountains under various erosion-sedimentation conditions that are assumed to represent the climate-controlled surface process. Numerical experiments show that with a relatively weak erosion-sedimentation strength, the crustal shortening is accommodated mainly by north piedmont of the Tianshan Mountains, similar to the high shortening rate of anticlines averaged over the last ~1 Ma. By increasing erosion-sedimentation strength, the resultant crustal shortening is transformed gradually toward the Tianshan Mountains, resulting in the shortening rate in its north piedmont being decelerated to what is observed as averaged over the last ~10±2 kyr. This result suggests that erosion and sedimentation could play an important role mechanically on strain localization across an intra-continent active tectonic belt. Hence, if the climate change around the last global deglaciation could be simply representative to the enhancement of surface erosion and sedimentation across the pre-existed Tianshan Mountains and its foreland, our models indicate that the observed shortening-rate variations averaged over ~1 Ma and ~10±2 kyr time scales around north piedmont of the Tianshan Mountains should be resulted from climate changes.