JOIDES RESOLUTION IODP Exp.391

Tristan-Gough-Walvis Ridge (WR) is a long-lived hotspot track that began with a continental flood basalt event (Parana, South America and Etendeka, Namibia, Africa) at ~132 Ma during the initial opening of the South Atlantic Ocean. The hotspot track stretches ~3300 km to the active volcanic islands of Tristan da Cunha and Gough, and it was originally paired with Rio Grande Rise (RGR) oceanic plateau in the western South Atlantic. The Tristan-Gough hotspot forms the most pronounced bathymetric anomaly of all Atlantic hotspots. Its age progression, chemistry, and connection to flood basalts point to a lower mantle plume source. The hotspot interacted with the Mid-Atlantic Ridge (MAR) during its early history, producing WR and RGR through plume-ridge interaction. Valdivia Bank, a plateau in the Walvis Ridge originally paired with the main part of Rio Grande Rise, may have formed a microplate, which may have disrupted the expected hotspot age progression. After producing a relatively uniform composition from ~120 to ~70 Ma, WR split into two or possibly three seamount chains with distinct isotopic compositions at about the time that the plume and MAR separated. The middle track may be a mixture of the outer two. The hotspot shows the longest-lived geochemical zonation known, covering about 70 Ma. Currently at ~400 km width with young volcanic islands at both ends, the hotspot track is wider than most other major hotspot tracks. Thus, WR displays global extremes with respect to (1) width of its hotspot track, (2) longevity of zonation, (3) division into separate chains, and (4) plume-ridge interaction involving a microplate, raising questions about the geodynamic evolution of this hotspot track. Understanding the Walvis Ridge is crucial for understanding the global spectrum of plume systems. To test hypotheses about mantle plume zonation, plume activity around a microplate, and hotspot drift, we plan to core at six locations along the Walvis ridge to recover successions of basaltic lava flows ranging in age from ~59 to 104 Ma. Samples will help us trace the geochemical evolution of the hotspot track as it became zoned, offering vital clues about compositional changes of the plume source and important implications for understanding the origin of hotspot zonation. Dating will show the age progression of volcanism both at individual sites and along the ridge, testing whether the Walvis Ridge formed as a strictly age-progressive hotspot track and whether Valdivia Bank formed as a plume pulse, extended volcanism around a microplate, or possibly even a continental fragment. Paleomagnetic data will track paleolatitude changes of the hotspot, testing whether hotspot drift or true polar wander, or both, explain changes in paleolatitude.