THE LATE CENOZOIC SW TARIM FORELAND BASIN: NEW CONSTRAINTS ON DEFORMATION AND SEDIMENTATION AT THE EDGE OF NW TIBET

We document large-scale Late Cenozoic to Recent thrusting and plate flexure in the SW Tarim basin at the northern margin of NW Tibet. The SW Tarim foreland basin is one of the largest in the world with a maximum thickness of orogenic-derived strata approaching 10km. This entire basin is translating to the NNE as the 230km long bedding-parallel Hotian thrust sheet, which is perhaps the longest active intact thrust sheet in the world. This thrust translates the growing Tarim foreland basin northward on a regional basal Cenozoic gypsum detachment and ramps to the surface at the northern edge of the flexural basin, forming the linear Mazhartag hills. At the southern edge of the basin a set of high-amplitude anticlines are growing by complex seismically active break-forward ramping and wedging in the Hotian thrust sheet as it steps up from a regional Cambrian evaporite detachment to the basal Cenozoic gypsum detachment. The more interior Tiklik thrust brings Paleozoic and Proterozoic basement to the surface, together with their uplifted Tarim basin cover. The total estimated shortening of SW Tarim basin crust is ~110-130km. The history of this deformation is constrained by growth strata imaged in long regional seismic-reflection profiles. We have determined the ages of key seismic horizons throughout the basin by tying the seismic grid to outcrop magnetostratigraphic sections in the foothills of the eastern Pamir and in Mazhartag and to dated ~11Ma volcanic deposits derived from an igneous center in the adjacent Pamir (Wei et al., 2018).