Estimation of paleostress orientation within deformation zones between two mobile plates

The orientation of the principal stress axes within deformation zones between two mobile plates is modeled analytically, using a thin-plate theory. The simple analytical approach helps to explain why plates cease to move after collision. Orogenic periods last only several tens of million years because the stress associated with a particular constant driving force (causing a constant strain rate) is no longer able to maintain a significant horizontal displacement. In contrast, the uplift rate increases rapidly as the horizontal velocity decreases, and this may explain why the termination of orogenic epochs are usually heralded by the rapid deposition of thick sequences of immature sedimentary rocks or flysch. The analytical model also elaborates the relationship between homogeneous bulk deformations driven by a constant stress orientation and those due to a fixed displacement direction of physical boundaries of the deformation zone. -from Author