Bathymetry of Valdivia Bank, Walvis Ridge, South Atlantic Ocean: Implications for Structure and Geologic History of a Hot Spot Plateau

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Contreras, E., García, P. Jiménez, Sager, W. W., Thoram, S., Hoernle, Kaj, Sarralde, R., Zhou, H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 2022
• Subjects: Gough; Mid-Atlantic Ridge; Tristan; South Atlantic Ocean
• Online Access: https://oceanrep.geomar.de/id/eprint/57410/; https://oceanrep.geomar.de/id/eprint/57410/1/ContrerasetalG3_2022.pdf; https://doi.org/10.1029/2022GC010624

Valdivia Bank is an oceanic plateau in the South Atlantic formed by hot spot magmatism at the Mid-Atlantic Ridge during the Late Cretaceous. It is part of the Walvis Ridge, an aseismic ridge and seamount chain widely considered to be formed by age-progressive volcanism from the Tristan-Gough plume. To better understand the formation and history of this edifice, we developed a bathymetric map of Valdivia Bank by merging available multibeam echosounder data sets with a bathymetry grid based mainly on satellite altimetry (SRTM15+). The bathymetric map reveals previously unresolved features including extensive rift grabens, volcanic mounds and knolls, and large-scale sediment transport systems. After Valdivia Bank was emplaced and probably eroded at sea level, it underwent a period of rifting, followed by a secondary magmatic pulse that caused regional uplift to sea-level, followed by subsidence to current depths. Shallow banks at depths of ∼1,000 m are the result of a thick sediment pile atop uplifted volcanic crust. Several shallower mounds (∼1,000–520 m) and a guyot (∼220 m) likely resulted from coral reef growth atop one or more volcanic pedestals formed during the younger Cenozoic magmatic event. As sediments accumulated on the shallow platforms, sediment transport systems developed as gullies, channels and mass transport deposits carved valleys and troughs, shedding sediment into abyssal fans at the plateau base. The new bathymetric map demonstrates that oceanic plateaus are geologically active long after initial emplacement. Key Points - A bathymetry map was constructed for Valdivia Bank from multibeam data merged with satellite altimetry-predicted depths - Valdivia Bank experienced extension, forming rifts, and secondary volcanism, uplift, and exposure, then was capped by carbonate sediments - Valdivia Bank shows evidence of mass wasting, partly triggered by Cenozoic uplift and erosion, but also owing to sediment cap instability