Passive margin subduction and the dynamics of collisional orogenesis

Abstract

Continental passive margins are characterized by a wide variety of geometries and widths. Whether these variations have an influence on subsequent dynamics of orogenesis is unresolved. To investigate, a series of upper mantle numerical experiments were performed with systematically varied continental margin widths and geometries. Results show that the vertical geometry of subducting continental margin crust controls both crustal and mantle lithosphere deformation. On both scales, end-members can be identified. Namely, break-off versus delamination of continental mantle lithosphere and double vergence versus single vergence of crustal thrust fronts form as a direct result of passive margin geometry. We find that the subduction of upper crust to depths >100 km promotes lithospheric delamination and is facilitated by an extended passive margin. Modeled orogens show decreasing upper plate deformation with increasing margin width. These results suggest that along-strike deformational variation within orogens may develop due to precollision passive margin geometry.