Collaborative Research: Late Cretaceous - early Cenozoic paleolatitude of the Walvis Ridge hotspot: Implications for true polar wander and hotspot geodynamics

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The Walvis Ridge is a volcanic ridge in the South Atlantic Ocean that was erupted on the African plate as it drifted over a hotspot, similar to the Hawaiian-Emperor seamount chain in the Pacific Ocean. Scientists are debating how accurately such hotspot tracks record plate motion. During the formation of the Emperor chain paleomagnetic data show that the hotspot moved southward by ~10-15°to its current location. This shift might be caused by movement of the hotspot. An alternate cause could be the shift of the Earth’s spin axis, or true polar wander (TPW). If TPW occurred, it should cause a consistent global shift: southward hotspot motion in the Pacific would be paired with northward hotspot motion in the Atlantic. This project will study volcanic rocks and sediments cored from Walvis Ridge during International Ocean Discovery Program Expedition 391 (December 2021-February 2022) to produce a record of paleolatitudes for comparison with Hawaii-Emperor paleolatitudes. The project supports several early career researchers.This project will analyze and publish studies of sediment and basalt core paleomagnetic data from IODP Expedition 391, with the object of developing a paleolatitude record for Walvis Ridge hotspot volcanoes for Late Cretaceous and early Cenozoic. IODP Expedition 391 drilled four sites, three on the Cretaceous Valdivia Bank plateau and one on a Paleocene guyot. Previous studies from Emperor and Louisville seamounts in the Pacific Ocean have been influential in studies of hotspot geodynamics. Prior to Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) drilling of Emperor seamounts, hotspots were considered fixed mantle markers, defining plate motions by seamount age progressions. DSDP/ODP cores showed that northern Emperor guyots were formed ~15° farther north than the current Hawaiian hotspot. IODP Expedition 330 cored coeval Louisville guyots, finding insignificant latitudinal motion, concluding that hotspot motion is the preferred explanation for inter-hotspot motion. Consequently, other explanations for hotspot latitude changes are not currently favored. One such phenomenon is true polar wander (TPW), the coherent shift of the entire mantle relative to the spin axis. TPW has been deemed insignificant for the past ~100 Ma, even though it is occurring at present and it has occurred deeper in the past. Hawaii and Louisville paleolatitude data show a small amount of mutual southward motion. If this results from TPW, the Walvis Ridge, almost antipodal to Hawaii and Louisville, should show the opposite paleolatitude change. This project will produce paleolatitude data for the Walvis Ridge using Expedition 391 cores (with data from DSDP Legs 72 and 74). A major objective is to test the hypothesis of Late Cretaceous-early Cenozoic TPW. This project hypothesizes that observed paleolatitude shifts are a combination of TPW and mantle flow. The project addresses important geodynamical problems that ultimately reflect mantle structure and convection. This project supports three early career investigators. In addition, the two faculty on this project will recruit undergraduate student workers from under-represented groups for internships that will help them advance in STEM education.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.