How do pre-existing weak zones and rheological layering of the continental lithosphere influence the development and evolution of intra-continental subduction?

Abstract

• The depth of a preexisting weak zone is one of the key factors in initiating intra-continental subduction. • Crustal internal friction angle plays an important role in altering the deformation type of a continental collision system. • The reactivation of the suture may be an auxiliary condition for the evolution of the south-dipping continental subduction underneath the North Pamir. Intra-continental subduction is of special importance for studying the formation of intra-continental orogens, crust-mantle structural evolution, and the far-field effects of continental collision, whose mechanism is still a matter of discussion. In this work, we investigated the role of pre-existing weak zones and the continental lithospheric rheological layering in the formation and evolution of the intra-continental subduction based on a 2D finite element numerical technique. The model results indicate that the deeper the intra-continental weak zone is and the faster the convergence velocity is, the more likely it is to develop into a new intra-continental subduction. Altering the rheological strength of the overriding plate may not have a substantial impact on the intra-continental subduction mode when the depth of the pre-existing weak zone is larger than half of the lithospheric thickness. In contrast, the lithospheric rheological strength is closely related to the continental collision system’s deformation style: Models with a weaker overriding plate are inclined to delaminate continuously under collision, whereas a strong overriding plate results in the subducting plate’s roll-back. The reactivation of the suture that runs deep into the lithosphere as a result of the Indian-Asian continental collision could be one of the crucial factors controlling the formation of the south-dipping subduction under the North Pamir.