Surface Forcing of Moho Topography in an Intra-Plateau Deep Basin

Unlike the wedge-shaped geometry typical of foreland basins, the interior of the Tibetan Plateau contains a series of large, closed basins. These basins are defined by thick sedimentary fills, a dish-shaped structural geometry, and a distinctly flattened to downward-convex morphology of the sub-basin Moho interface. However, the mechanisms governing their evolution remain debated. To address this, we employed numerical models that couple surface processes with lithospheric rheology to simulate the Cenozoic evolution of the Qaidam Basin, the largest sedimentary basin within the Tibetan Plateau, which has continuously accommodated substantial sediments derived from the surrounding mountain ranges throughout the Cenozoic. By systematically varying parameters from high to low erosion rates and from normal to strong mantle rheology, we compared model outcomes and successfully reproduced the observed geometry, topography, sedimentary sequence, and sub-basin Moho morphology of the Qaidam Basin. Our models reveal that dish-shaped basin evolution is controlled by three key factors: substantial sediment loading, a low crustal convergence rate, and a persistent centripetal sediment routing system. The sediment loading suppresses crustal deformation within the basin and drives downward deflection of the sub-basin Moho. Concurrently, a stronger mantle lithosphere localizes the deformation, resulting in a shorter-wavelength basin geometry. Our findings provide a new perspective for understanding deep intra-plateau basins by highlighting the governing role of coupled surface processes and lithospheric rheology. This mechanism not only explains basins within the Tibetan Plateau but also accounts for analogous settings, such as the Altiplano Basin in the Altiplano-Puna Plateau. Furthermore, the model is applicable to other dish-shaped basins formed under similar coupling conditions, exemplified by the Junggar Basin. Another key finding is that active surface processes can drive subsurface exhumation even under stable tectonic conditions. This suggests that accelerated cooling signals recorded by low-temperature thermochronology may not solely represent tectonic uplift acceleration, thereby implying that such data require careful reinterpretation.