Influence of tectonic setting and extension velocity on the basement architecture of rifted continental margins

Magma-poor rifted margins portray a wide range of tectonic styles. These differences arise from the variability in key factors controlling continental rifting, such as the initial lithospheric strength and extension velocity. The aim of this work is to use thermomechanical numerical experiments to shed light on the processes controlling the modes of continental extension and their impact on margin tectonic architecture and nature of the continent-ocean transition (COT).

Firstly, I further developed a 2D thermodynamic model by including melt productivity, melt emplacement below the extending continental crust, heat release by the emplaced melt and serpentinization. Additionally, I carried out a series of sensitivity tests of the main parameters controlling the evolution of the model in order to establish appropriate conditions for the pre-rift lithospheric structure and for the involved mechanisms.

Secondly, I systematically varied the lower crustal strength and extension velocity to analyze the modes of extension, distribution of surface heat flow and crustal and lithospheric depth dependent thinning (DDT). I showed how different types of lower crustal flow localize upper crustal faulting either in single or multiple faults. This type of flow is linked to the formation of a low viscosity channel within the deep crust, whose extent and thickness varies with the mode of extension (i.e. narrow, sequential faulting, wide and core complex). The distribution of crustal DDT in our models was compared to natural rifted margins, and inferred that the lower crustal flow generally occurs at a fault-block scale, which induces small-scale crustal DDT, except for the core complex extensional mode.

Finally, I showed the importance of the lower crustal strength in controlling also the amount and onset of melting and serpentinization during rifting. I proposed that the relative timing between both events controls the nature of the COT. Subsequently, I presented a genetic link between margin tectonic style and nature of the COT that strongly depends on the lower crustal strength. Based on this conceptual template, I predicted different natures for the COTs in the South Atlantic central segment.