Slide 27 of 50

Gravity Driven Deformation: The Concept of Gravitational Collapse. Gravitational collapse corresponds to the decay of lateral contrast in gravitational potential energy that builds up during lithospheric thickening. When the forces that support this anomaly (tectonic forces and the strength of the deformed and the surrounding lithospheres) decrease, the gravitational potential anomaly may relax. Two end-member modes of collapse are defined depending on the behaviour of the lithosphere surrounding the deformed domain. When the surrounding lithosphere is fixed (fixed-boundary collapse) collapse occurs through a transfer of gravitational potential energy from the elevated regions toward the lowlands. This transfer is accommodated by a combination of gravitational sliding of the brittle crust and horizontal gravitational spreading of the lower crust. In orogenic domains, fixed-boundary divergent collapse implies the lateral growth of the orogenic domain at the expense of the surrounding lithosphere. In contrast, when the surrounding lithosphere is free to move (free-boundary divergent collapse) the thickened crust is homogeneously thinned without transfer of gravitational potential energy toward the forelands.