Exploring the earliest stage of magmatic break-up through numerical simulations

In the early stages of continental rifting, a considerable volume of both mafic and felsic magmas can be formed. These magmas originate from the mantle and lower crust respectively, and their composition and volume are related to the localization and potential jumps of the rifting centers. An excellent illustration of these magmatic and tectonic processes are the aborted rift systems along the South Africa and Namibia volcanic passive margins and the eastern Afar area. In order to investigate these processes, we have used a thermo-mechanical numerical modelling approach based on the marker-in-cell method. Our experiments reveal that under the combined presence of far-field tectonic extension and thermal anomalies, partial melting in the upper mantle first generates large amounts of erupted basalt that forms traps and early conjugate SDRs (Seaward-Dipping Reflectors). Subsequently, melting of the lower crust and re-melting of mantle-derived intrusions produce felsic magmas at a later stage of rifting shortly preceding the lithospheric break-up phase. As the lithosphere thins, the rifting center may migrate laterally and crustal anatexis becomes inactive. As a result, the SDRs packages are laterally continuous and the early rift systems subsides, hosting the latest felsic magma extrusives. Throughout the evolution of the magmatic rift system, the production of mafic melts is primarily controlled by the location of thermal anomalies in the upper mantle.