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- Title
Bathymetry of Valdivia Bank, Walvis Ridge, South Atlantic Ocean: Implications for Structure and Geologic History of a Hot Spot Plateau.
- Authors
Contreras, E.; García, P. Jiménez; Sager, W. W.; Thoram, S.; Hoernle, K.; Sarralde, R.; Zhou, H.
- Abstract
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. Plain Language Summary: Valdivia Bank is an oceanic plateau in the South Atlantic that was formed as part of Walvis Ridge by hot spot volcanism at the Mid‐Atlantic Ridge. Walvis Ridge topography is more complex than that of simple hot spot tracks. Moreover, younger‐than‐expected ages from dredge samples suggest a second phase of volcanism. To better understand the development of this plateau, we created a detailed bathymetry map by compiling available multibeam echosounder data with satellite‐altimetry‐based depth estimates. The map reveals previously unseen features including rifts, volcanic mounds, and submarine slides and sediment drainage features. These suggest that after Valdivia Bank formed, it underwent faulting, followed by volcanism that raised the plateau to sea level. Subsequently, the plateau subsided while accumulating a thick sediment cover. Shallow banks resulted from thick sediments atop the uplifted basement. Several shallower mounds likely resulted from coral reef growth atop a volcanic base formed during the later stage of volcanism. As sediments accumulated atop the plateau, they were shed through gullies, channels and submarine slides, carving valleys and troughs, and then deposited around the plateau base. Our findings demonstrate that oceanic plateaus can be geologically active long after their formation. Key Points: A bathymetry map was constructed for Valdivia Bank from multibeam data merged with satellite altimetry‐predicted depthsValdivia Bank experienced extension, forming rifts, and secondary volcanism, uplift, and exposure, then was capped by carbonate sedimentsValdivia Bank shows evidence of mass wasting, partly triggered by Cenozoic uplift and erosion, but also owing to sediment cap instability
- Subjects
MID-Atlantic Ridge; GEOLOGIC hot spots; OCEANIC plateaus; VOLCANISM; BATHYMETRIC maps; SUBMARINE fans; SEDIMENT capping; SUBMARINE volcanoes
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2022, Vol 23, Issue 11, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2022GC010624