A strain-rate-dependent force model of lithospheric strength

Abstract

Summary This study investigates the rate of intraplate deformation, the vertically integrated stress magnitude and vertical distributions of tectonic stress in continental lithosphere that is subjected to horizontal tectonic force. The fundamental assumption of this study is that the magnitude of the imposed tectonic force depends on the rate of deformation. This modification of the often applied strength envelope concept accounts for resistance forces generated externally to the lithospheric section that the calculated vertical stress distribution is considered to represent. The model presented overcomes the difficulties that arose in previous constant strain rate and constant force approaches and thus proves to be physically more realistic. Results are discussed with emphasis on the effects related to the strain-rate-dependent force assumption and on differences from the results of both previous approaches. The strain-rate-dependent force model predicts that in and adjacent to a weak and fast-deforming lithospheric plate, the integrated stress magnitude is significantly reduced due to externally derived resistance forces. Modelling results suggest that the rate of intraplate deformation in many cases is controlled by the balance of externally derived deformation-driving and externally derived deformation-resisting forces, but is relatively insensitive to the low internal strength of the deforming lithosphere. The integrated stress level in regions of active intraplate deformation, in contrast, is predicted to be largely controlled by the time-independent brittle strength. The strain-rate-dependent force model provides a geodynamic concept that allows one to investigate intraplate stress distribution depending on tectonic force magnitude, lithospheric strength and rate of intraplate deformation.