Gravity-driven crustal shortening in failed rifts

Abstract

It is proposed that gravity-driven crustal shortening, caused by the potential energy of marginal uplifts adjacent to thinned crust in a rift zone, occurred immediately after rifting ceased in both the Gulf of Suez and North Sea rifts. Compressional stresses of the order of 1–2 MPa would have been generated which were relieved by finite contractional strains of the order of 2–5%. Shortening of this magnitude has been observed as post-rift contractional structures in the western Sinai, Gulf of Suez and the Viking Graben, North Sea. These observations are compatible with a physical model for stresses generated in the crust due to lateral variations in crustal thickness. This model helps to explain some apparently anomalous structures within rifts such as tight hanging-wall folds; some aspects of fault block rotation, footwall uplift and tilting; and also has important implications for the formation of unconformities and the redistribution of sediments in rifts. The phenomenon of gravity-driven crustal shortening in failed rifts may have occurred in other major, intra-cratonic rifts.