Cenozoic pure-shear thickening of the northern Tibetan Plateau margin: Implications for diverse plateau uplift mechanisms controlled by convergent obliquity

How the deformed Tibetan lithosphere absorbed the convergence of India and Eurasia during the Cenozoic remains enigmatic, primarily due to significant variation in lithospheric deformation across different margins of the plateau. The northern margin of the Tibetan Plateau is uniquely defined by the ∼1600-km-long Altyn Tagh fault system. How this plateau margin uplifted for 2−4 km under a strike slip-dominated deformation regime remains a subject of debate. Understanding the SE Tarim Basin north of this plateau margin is crucial for addressing this issue, as it contains thousands of meters of Cenozoic sediments sourced from the Tibetan Plateau. Here we use well-logging, isopach mapping, and seismic reflection data to characterize the Cenozoic deposition and deformation processes of the SE Tarim Basin, which are closely related to the uplift mechanism of the northern plateau margin. The results show that (1) the Cenozoic strata exhibit minimal variations in thickness, with no evident thickening toward the Tibetan Plateau; (2) the basin has been deformed by high-angle, basement-involved compressional faults since ca. 16 Ma, mainly through the reactivation of pre-Cenozoic structures; and (3) the maximum Cenozoic shortening is merely ∼0.9 km in the area we studied. These findings, integrated with other geological and geophysical observations, argue against the long-distance continental subduction of the Tarim Basin beneath the Tibetan Plateau, which requires the development of a foreland basin with sediments thickening toward the orogen and low-angle, thin-skinned fold-thrust belts involving ∼100−150 km of shortening in the SE Tarim Basin. These results, together with vertical Moho offsets across the fault system, lead us to propose lithospheric-scale pure-shear thickening as the Cenozoic uplift mechanism of the northern Tibetan Plateau margin. By further comparing the various uplift mechanisms operating on different margins of the Tibetan Plateau, we emphasize the significant role of convergent obliquity in controlling diverse plateau uplift mechanisms.