Teleseismic traveltimes, topography and the lithospheric structure across central Mongolia

Abstract

Teleseismic travel times recorded along a 1000 km‐long, ∼N‐S transect across central Mongolia are used together with topography and gravity data to constrain the deep lithospheric structure of this region. Time residuals appear positively correlated with the topography, suggesting that P‐wave velocity changes correspond to density variations which in turn cause an isostatic uplift of the topography. Using a simple local isostasy model and a Monte‐Carlo inversion for the crust and asthenosphere velocities and density/velocity conversion factors, we determine best‐fitting Moho and lithosphere‐asthenosphere boundary (LAB) geometries which satisfyingly reproduce the observed topography and gravity data. The model is validated using previously published 1D S‐wave velocity models obtained from receiver function analyses. Our results indicate that most of the long‐wavelength topography is supported by the asthenosphere buoyancy. The Hangai dome, in the southern half of the transect, appears mainly supported by a rather shallow (60–70 km) asthenospheric uplift, whereas the Siberian platform at the extreme north of the profile is underlain by a very thick (∼200 km) lithosphere. Misfits to the observed Bouguer gravity anomaly occur near major faults, probably because of lithospheric flexure.