Lithospheric elastic thickness estimates in central Eurasia

Abstract

We estimate the elastic thickness of a continental lithosphere by using two approaches that combine the Vening Meinesz-Moritz (VMM) regional isostatic principle with isostatic flexure models formulated based on solving flexural differential equations for a thin elastic shell with and without considering a shell curvature. To model the response of the lithosphere on a load more realistically, we also consider lithospheric density heterogeneities. Resulting expressions describe a functional relation between gravity field quantities and mechanical properties of the lithosphere, namely Young's modulus and Poisson's ratio that are computed from seismic velocity models in prior of estimating the lithospheric elastic thickness. Our numerical study in central Eurasia reveals that both results have a similar spatial pattern, despite exhibiting also some large localized differences due to disregarding the shell curvature. Results show that cratonic formations of North China and Tarim Cratons, Turan Platform as well as parts of Siberian Craton are characterized by the maximum lithospheric elastic thickness. Indian Craton, on the other hand, is not clearly manifested. Minima of the elastic thickness typically correspond with locations of active continental tectonic margins, major orogens (Tibet, Himalaya and parts of Central Asian Orogenic Belt) and an extended continental crust. These findings generally support the hypothesis that tectonically active zones and orogens have a relatively small lithospheric strength, resulting in a significant respond of the lithosphere on various tectonic loads, compared to a large lithospheric strength of cratonic formations.