Modes of Extension and Oceanization at Magma-Poor Margins: An Example from the Brazilian-African Margins

Abstract:

It is well known that the amount of magmatism and occurrence of serpentinised mantle at rifted margins and oceanic ridges fundamentally depends on spreading rate and mantle potential temperature. Here we show that during continental extension the lower crustal strength exerts an additional fundamental control on the onset and amount of melting and serpentinisation and therefore the type of oceanization. Furthermore, using numerical modeling constrained by multi-channel seismic reflection and wide-angle data from the magma-poor margins of Brazil and Africa, we also show that it is possible to associate margin architectural styles to types of ocean-continent transitions. Observed margin architectural styles can be explained by a combination of extensional modes: core-complex, wide and narrow (Buck, 1991), with a fourth mode, sequential faulting, that accounts for conjugate margin asymmetry (Ranero & Perez-Gussinye, 2010, Brune et al., 2014). The prevalence of any of these modes during extension, which depends on lower crustal strength, controls mantle uplift velocity and hence the relative amounts and timing of melting and serpentinisation, and the character of the ocean-continent transition.