Mantle flow beneath western Mongolia: Evidences from lithospheric flexure analysis

The origin of the high-elevation and neotectonism of western Mongolia remains enigmatic. Several studies suggested that the mechanisms might, at least in part, lurk in the mantle, but little consensus was reached on its pattern and contributions to the surface topography. Geophysical and geodynamical studies indicated that the viscous stresses exerted by mantle flow can maintain a substantial proportion of topography and gravity anomaly, resulting in a high long-wavelength free-air admittance and dynamic topography. These two estimates are commonly used as indicators to detect mantle flow. In this study, we provided evidence for mapping mantle flow beneath western Mongolia by lithospheric flexure analysis in terms of the relationship between gravity anomaly and topography. Our results show a significant dynamic topography of an amplitude over 500 m and a high long-wavelength free-air admittance of value over 35 mGal/km in the southwestern part of western Mongolia, leading to a reliable argument for mantle upwelling beneath western Gobi Altai. We also reveal that the long-wavelength free-air admittance deviates from lithospheric flexure isostasy in the Hangai Dome. Combined with other studies, we infer that horizontal flow fed by the upwelling from western Gobi Altai supports the Hangai Dome uplift. Our results demonstrate the significant role of mantle flow in shaping the present-day anomalous topography and tectonism in western Mongolia, central Asia.