Extension of continental lithosphere in rifted margins: a review of thinning mechanisms

Abstract

Crustal geometries imaged at rifted margins show contrasted first-order morphologies (wide and narrow, symmetric or asymmetric conjugates). This contribution aims to review the mechanisms of continental lithospheric thinning and types of extensional structures that control the formation of rifted margins. We illustrate, using a two-layer numerical model (one for the crust and one for the mantle), how different modes of lithospheric thinning shape the end-member crustal geometries of rifted margins depending on the initial thermal conditions and extension rates. As already known, the activation of narrow or wide modes of lithospheric thinning depends on the rheological behaviour of the lower crust and its efficiency as a decoupling layer. Morphologies generated by narrow lithospheric thinning modes compare well with Atlantic-type rifted margins (e.g., Iberia-Newfoundland) while wide lithospheric thinning modes better apply to marginal seas characterized by higher initial geothermal gradients (e.g., South China Sea). Finally, we also emphasize that continental lithosphere thinning is depth-dependent, part of which is transient and cannot easily be measured in natural systems.