Timing of the Tianshan Mountains uplift constrained by magnetostratigraphic analysis of molasse deposits

The Tianshan Mountains lie in the actively deforming part of the India–Asia collision zone. The thrust faulting and folding of the Neogene and Quaternary sediments, forming linear, roughly east–west anticlines at the northern and southern borders of the orogenic belts, indicate crustal shortening and thickening in late Cenozoic time. Detailed magnetostratigraphic studies of the molasse deposits of the folded Neogene and Quaternary strata in the northern edge of the Tianshan Mountains indicate that the onset of uplift occurred at ∼7 Ma. Deposition of the thick conglomerates between 7 and 2.58 Ma in the studied region was mainly in response to the tectonic uplift, while the accumulation of the early Pleistocene conglomerates (Xiyu Formation) was mostly controlled by both tectonics and climatic cooling. Our results indicate that the present high relief of the Tianshan Mountains is the result of two dominant phases of uplift occurring at about 7–2.58 Ma and the early Pleistocene.