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.
Highlights
The elastic thickness of the lithosphere defines its integrated strength in response to various tectonic loads, while depending on the lithospheric density structure and its rheological properties
We first briefly recapitulate the Vening Meinesz-Moritz (VMM) and flexural isostatic theories and combine them in order to determine the elastic thickness of a continental lithosphere based on solving flexural differential equations for a thin elastic shell with and without considering the shell curvature
Differences between the elastic thickness estimates are only caused by disregarding the shell-curvature term in the definition of degree-dependent compensation coefficients Cn given in Eq (12), meaning that if we disregard the shell curvature the load is entirely compensated by bending stresses
Summary
The (effective) elastic thickness of the lithosphere defines its integrated strength in response to various tectonic loads, while depending on the lithospheric density structure and its rheological properties. Large values of the continental lithospheric elastic thickness apply typically to old cratonic formations, while the elastic thickness of active tectonic margins and young orogens is relatively small. Various methods were developed and applied to estimate the lithospheric elastic thickness. 195) is probably the most commonly used method for the elastic thickness estimation; see studies, for instance, by Calmant et al (1990) for the non-spectral inverse gravity modelling techniques to determine the elastic thickness along Indo-Eurasian continental collision zone. Tassara (2005) applied the flexural analysis along Andean margin and Tassara et al (2007) used the wavelet form of a classical spectral isostatic analysis for South American and surrounding tectonic plates. Galán and Casallas (2010) applied the admittance analysis to estimate the elastic thickness of Colombian Andes. Tesauro et al (2013) presented the global model of the lithospheric elastic thickness, while considering variations of Young’s modulus within the lithosphere, and Tesauro et al (2018) took into consideration temperature, composition and strain rates of the lithosphere
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