Crustal Doming and the Mechanism of Continental Rifting

Abstract

Bott, M.H.P., 1980. Crustal doming and the mechanism of continental rifting. In: J.H. Illies (Editor), Mechanism of Graben Formation. Tectonophysics, 73: 1–8. A mechanical explanation of the relationship between crustal uparching and graben formation is suggested, based on the geologically supported assumption that doming precedes rifting. Rifting and graben formation can occur under conditions of crustal tension by the Vening Meinesz wedge subsidence mechanism modified to apply to the uppermost 20 km or thereabouts of the continental crust. If sediment-filled troughs of around 5 km depth are to be formed by this mechanism, then a persistent tension of about 200 MPa (2 kbar) is required. Such a stress system may result from the combined effect of the topographic load of the uplifted region and the upthrust caused by the underlying low-density upper mantle region below. If the upper 10 to 20 km of the crust is elastic but the underlying region can deform slowly by visco-elastic creep, then stress differences of the order of 200 MPa can occur in the upper elastic crust by this process. It is suggested that such a stress system, rather than one arising from bending of the uparched crust or from plate boundary stresses, may be the primary cause of the rifting.