Strike‐slip deformation and expansion process of the Qilian fold‐and‐thrust belt: Inferred from gravitational potential energy

Abstract

In this study, we present a new estimation of the gravitational potential energy (GPE) and explore its relationship with the present‐day stress and strain‐rate field in the Qilian fold‐and‐thrust belt (QFTB), to evaluate how the stress associated with GPE gives rise to tectonic deformation of the QFTB, and to achieve a more comprehensive understanding of stress transfer from the Indian–Eurasian collision belt to the QFTB. Significant features of the stress and deformation in the QFTB derived from our analysis include the following: (1) the stress pattern is verified by the results of the deviatoric stress being inverted by topographic stress modelling, suggesting that topographic stress associated with the lateral variations in crustal thickness and topography should be taken into account when considering the clockwise rotation of the stress field along the strike of the Qilian fold‐and‐thrust belt. (2) Our stress–strain results suggest that the strain derived from the Indian–Eurasian convergence propagated to the north of the Haiyuan Fault. By incorporating with recent seismological results, it is supposed that the Tibetan Plateau has extended to the southern Alxa block, and the Haiyuan Fault may not be the most northeastern crustal boundary of the Tibetan Plateau. (3) The comparison of surface strain, focal stress and topographic stress modelling illustrates that the Qilian fold‐and‐thrust belt is probably deforming in response to the far‐field effect of Indian–Eurasian convergence. The stress transfer from the collisional front to the Qilian fold‐and‐thrust belt appears to be continuous and progressive. Accordingly, we suggest that a diffuse model could better describe the deformation of the Qilian fold‐and‐thrust belt in which lateral expansion is accommodated evenly along the principal axes of stress as a consequence of horizontal lithospheric heterogeneity.