Continental Deformation in Central Eurasia: Insights From a Neotectonic Study

Abstract:

The Central Eurasia region hosts wide deforming areas, with diffused or localized deformation occurring even hundreds of kilometres behind the Arabia-Eurasia and India-Eurasia plate boundaries. A key-parameter controlling the propagation of deformation to the continent interiors is the lithosphere strength. By using a numerical technique based on the thin-sheet approximation, we explore the present-day deformation in Central Eurasia and the relative contributions of the lithospheric structure, rheology, boundary conditions, and friction coefficient on faults on the predicted velocity and stress fields. The lithosphere strength is calculated from the lithosphere structure and thermal regime.

A crustal and lithospheric map derived from the combination of elevation and geoid anomaly with thermal analysis, showing thin lithosphere beneath the Iranian Plateau and thick lithosphere beneath the Tibetan Plateau, is used to build a reference model. Changes in the rheological parameters, friction coefficient on faults and velocity boundary conditions have been applied. A model with thin lithosphere in NE-Tibet following previous geophysical studies has been also considered. Models have been evaluated by comparing the predictions with available data on seismic deformation, stress directions and GPS velocities.

A first order approximation of the velocity and stress directions is obtained, reproducing the counter-clockwise rotation of Arabia and Iran, the westward escape of Anatolia, and the eastward extrusion of the northern Tibetan Plateau. To simulate the observed extensional faults within Tibet a weaker lithosphere is required, provided by i) a change in the rheological parameters or ii) reduction of the lithosphere thickness in NE-Tibet. The temperature increase generated by the lithospheric thinning would allow also reconciling the model with the high heat flow and low mantle seismic velocities observed in the area.