Deciphering the rheological, stratigraphic and thermal evolution of magma-poor rifted margins: coupling thermo-mechanical models with observations and interpretations from seismic reflection data.

Interpretations derived from crustal-scale seismic reflection datasets across the Newfoundland and Angola-Brazil margins are used as input for thermo-mechanical models. Numerical models that replicate the first-order crustal geometries highlight possible geodynamic processes that may have occurred to create the rifted margin structures and accommodation space observed today. Numerical experiments are used to quantify and display, in a coherent way, the temporal and spatial evolution of rift-related processes (e.g., mechanical, thermal, magmatic, sedimentary) for the whole rift evolution.

Observations suggest that basement heat-flow evolves in relation to the dynamic rift process and sedimentary loading. Rifting can fail, but it appears that the process of successful coupling between the brittle upper crust and mantle is the point at which rifting processes rapidly localize. This coupling of the upper crust and mantle may enable hot mantle-derived fluids to circulate, overprinting the already elevated “background” conductive heatflow that results from the process of crustal thinning.

Our models highlight the importance of crust and mantle rheology in defining the thinning processes leading to hyperextension and depth-dependent extension. Necking occurs in both the crust and the mantle. Once strain has localized and coupling between the upper crust and the brittle upper mantle occurs we observe significant changes in the evolution of rifting. Coupling of the brittle-ductile layers sets up the H-Block structure, and mecahnically forces localization basinwards in accordance with the observation of the creation of a necking unconformity over the future proximal margin. In addition our models highlight that syn-tectonic sedimentary supply/facies (e.g. salt), and magmatic budgets have an influence upon the evolution of subsidence and heatflow and the onset of seafloor spreading processes across magma poor rifted margins.