Volcano-sedimentary evolution of the Walvis Ridge (IODP Expedition 391)

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IODP Expedition 391 along the Walvis Ridge (WR) will provide a unique opportunity to reconstruct the geological evolution of several submarine volcanic edifices considered to have formed due to hotspot volcanism on a slow-moving ocean plate. Previous drilling of the WR during DSDP Legs 39, 40, 74 and 75 recovered a large diversity of volcaniclastic deposits that suggest recurring formation of volcanic islands since the Late Cretaceous. However, our understanding of their formation and evolution remains hampered by very limited drilling. Similarly, the long-term geological (constructional and erosional) evolution of drown hotspot islands globally is still poorly understood due to difficulties to access and characterise their summit geology; consequently, existing models of oceanic island formation are based on observations from a limited selection of subaerial volcanic edifices that are much younger and/or unusually large compared to the vast population of unstudied seamounts thought to represent ancient oceanic islands. The proposed research will help address this observational bias through a lithofacies and geochemical characterisation of volcano-sedimentary sequences to be retrieved during Expedition 391 from the top of WR guyots. This will allow to test whether the evolution of the Ridge was accompanied by the formation of ephemeral oceanic islands, and whether the evolution of these possible islands was similar to that of other modern and ancient hotspot intraplate volcanoes in the Atlantic and Pacific Oceans. Ultimately, this will help develop an improved model of formation and evolution of large intraplate oceanic volcanoes.