Walvis Ridge Hotspot: drilling Walvis Ridge, Southeast Atlantic Ocean, to test models of ridge-hotspot interaction, isotopic zonation, and the hotspot reference frame1
Published April 2020
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Walvis Ridge (WR) is a long-lived hotspot track that began with a continental flood basalt event at ~132 Ma during the initial opening of the South Atlantic Ocean. WR 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. Because of the duration of its volcanism and the length of its track, 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, projected to be the hypothesized plume generation zone at the margin of the African large low shear-wave velocity province. The hotspot interacted with the Mid-Atlantic Ridge (MAR) during its early history, producing WR and RGR through plume-ridge interaction. Valdivia Bank, a WR plateau paired with the main part of RGR, represents heightened hotspot output and may have formed with RGR around a microplate, disrupting the expected hotspot age progression. After producing a relatively uniform composition from ~120 to ~70 Ma, WR split into three seamount chains with distinct isotopic compositions at about the time that the plume and MAR separated. With ~70 My spatial zonation, the hotspot displays the longest-lived geochemical zonation known. Currently at ~400 km width with young volcanic islands at both ends, the hotspot track is far wider than 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 WR is critical for knowledge of the global spectrum of plume systems. To test hypotheses about mantle plume zonation, plume activity around a microplate, and hotspot drift, we propose coring at six locations along the older ridge to recover successions of basaltic lava flows ranging in age from ~59 to 104 Ma. Samples will help us trace the evolution of geochemical and isotopic signatures as the hotspot track 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 WR 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.
This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license.