3D Thermo-mechanical models of Equatorial Atlantic rifting and opening, and the oblique/transform continental margins formation and evolution - Preliminary results

Transform continental margins pose major questions, such as the role of inheritance in their opening, the timing of formation in relation to the first oceanic accretion, and the horizontal and vertical movements during their polyphased and diachrone evolution. The Equatorial Atlantic Ocean opened during Early Cretaceous between the Guiana/Guaporé Craton and the West African craton. The rift and oceanic opening occurred obliquely compared to the direction of extension, producing a number of conjugated divergent, oblique and transform margins. In order to understand the processes involved in margin formation and evolution, we set up 3D thermo-mechanical models of continental rifting. pTatin3D, an open source code, is used to solve for Stokes flow coupled with diffusion advection energy solver. This ALE code allows for large strain with inflow and outflow boundary conditions as well as for producing realistic topography (free surface).Two preliminary set ups have been tested: The first one consists at testing the influence of the background stress field on the direction of propagation of a rift. In order to test that, we apply some stretching or shortening normal to the main direction of extension of the model. An elongated localized damaged zone located at the southern edge of the model, which represents the Southern Atlantic, triggers the location of the first rift.The second set up consist at testing the role of pre-existing suture zones such as the Rokelides panafrican. In this model, we introduce different degrees of coupling between the lower crust and the mantle depending on the cratonic or mobile nature of the lithosphere and study how the rifting propagates trough. In both cases, we note that the formation of the OCT leads to a redistribution of the stress in the lithosphere that favors the oblique propagation of rifting and the formation of oblique margins. However, without pre-existing sutures, pull-apart and true transform margins do not seem to occur with our set up.