Insights into plume-ridge-transform fault interactions as derived from 3D numerical geodynamic modelling of the Azores Triple Junction

The Azores Archipelago is an igneous province located in the centre of the Atlantic Ocean marked by a large bathymetric plateau with a complex tectonic history. Over the last 10 Myr, this region has been shaped by the interaction between the Azores plume, the Mid-Atlantic Ridge (MAR), and the Gloria Fault zone. This complex interaction was characterised namely by the transition from a ridge-ridge-transform (R-R-T) triple junction to a diffuse complex triple zone, with the implied tectonic stresses being accommodated along several right-lateral oblique extensional structures, including the Terceira Rift. An understanding of the main geodynamic mechanisms behind this transition is still lacking. This work explores how the Azores system may have been shaped by these complex plume-ridge-transform fault interactions by running 3D viscoelastoplastic geodynamic models using the LaMEM code. We base our initial modelling setup on previously proposed reconstructions for Azores during the Early Miocene, and implement a complying shift from spreading to right-lateral regional strain rate conditions. We further implemented a plume rising below the MAR to gain additional insight on the nature of the main geodynamic process-interactions governing this system. Our results suggest that the present-day geometric configuration of the Azores, as well as the formation of the Terceira Rift, are strongly conditioned by the interactions between plume-ridge-transform fault system under the right-lateral relative motion between Eurasia and Nubia, as well as by the growth of the Azores Plateau. Under our modelling conditions, a thicker and weaker Azores Plateau, interfering with a mantle plume, promotes the localisation of deformation along its edges which act as rheological boundaries. As a consequence, the global shift in tectonic forcing is shown to be capable of strongly localize strain along the NE edge of the plateau, closely mirroring the present-day location of the Terceira Rift.