The evolution of structure of crustal flow and relief of epi-platformal orogens effected by small-scale convection in the asthenosphere

Abstract

The problem of the evolution of the state of stress and surface topography of the crust and upper mantle is studied using the method of analytical modeling. The source of the deforming effects on the lithosphere is the thermogravitational convection in the asthenosphere. This impact has been presented in the form of perturbations of horizontal component of the velocity vector on the bottom of a two-layer viscous two-dimensional model of the lithosphere, where the upper layer of the two-layer lithosphere is the crust, and the bottom layer is the upper mantle. We used the method of separation of variables: the perturbation as well as all other functions of the mechanical state of the system were searched in the class of laterally harmonic functions. The investigation showed that the development of crust deformation at the roof is accompanied first by inversion of sign of the vertical component of movement fallowed by inversion of the sign of the roof crust relief resulting in a change in the nature intracrustal flow. The subsequent evolution of the system takes place towards the isostasy state of lithosphere. On the final stage there a certain of level of deviation from the isostasy. Additionally the authors studied the effect of denudation and accumulation processes on the emerging state of the lithosphere. Estimations of these processes were made by modifying the boundary conditions on the main interfaces of the lithosphere. Interpretation of the results suggests that small-scale convection in the asthenosphere is supposed to be one of the major factors responsible for the formation of the state of stress epi-platformal Orogens.