Age and radiogenic isotope geochemistry of the Agulhas Plateau (SW Indian Ocean) drilled during IODP Exp. 392

The Agulhas Plateau is an oceanic plateau located in the gateway between the South Atlantic and Indian Oceans. It is thought to have formed during the late Cretaceous together with the Maud Rise (MR) and Northeast Georgia Rise (NEGR) as a joint plateau. Igneous rocks, cored from the volcanic basement of Agulhas during IODP Expedition 392 (Uenzelmann-Neben et al., 2023, IODP Proceedings 392), include tholeiitic sills and pillow lavas. ⁴⁰Ar/³⁹Ar ages range from 78.61 ± 0.68 to 87.36 ± 0.19 Ma. Lavas from the Agulhas sites were also analyzed for Sr-Nd-Pb-Hf isotopic composition together with newly sampled legacy core samples from MR (ODP Leg 113) and NEGR (ODP Leg 114). The Agulhas rocks are less enriched compared to the adjacent and slightly older Mozambique Ridge lavas, which trend towards an “enriched mantle” composition (Jacques et al., 2019, Chem. Geol. 507). Instead, the Agulhas lavas show systematically lower initial ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios for a given ²⁰⁶Pb/²⁰⁴Pb and thus plot closer to the Northern Hemisphere Reference Line while forming a trend towards the Bouvet hotspot composition. In contrast, analyzed MR and NEGR lavas have a more enriched isotopic composition similar to Mozambique Ridge. In the light of these results and applying new plate tectonic reconstructions, we discuss if Agulhas shared a common magma source with MR and NEGR or whether the latter two plateaus formed as part of the earlier Mozambique event, which would result in a revised geodynamic history of oceanic plateau formation in the southern African marine gateway.