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GEOPHYSICAL ANALYSIS OF ANOMALOUS EXTRUSIVE VOLCANISM IN SOUTH ATLANTIC OCEANIC CRUST
Observations from multibeam bathymetry and backscatter data indicate varying amounts of extrusive volcanism across the dataset. Generally, with some exceptions, as crustal ages increase away from the ridge, volcanoes and small-scale crustal features are masked by sediment so that only large-scale features are visible on the seafloor. The most notable exception is a ~31 Ma (24 mm/yr half spreading rate) ridge-parallel ~2500 km2 transect of crust which exhibits an anomalous presence of extrusive volcanoes compared to the rest of the survey. At this ~31 Ma transect, we distinguish upwards of 50 volcanoes present on the seafloor. In contrast, other ~2500 km2 transects on the survey with crustal ages of ~7 Ma (19 mm/yr half rate), ~15 Ma (25 mm/yr half rate), ~48 Ma (19 mm/yr half rate), and ~63 Ma (15 mm/yr half rate), exhibit ~28, ~20, ~11 and ~7 volcanoes on the seafloor, respectively.
Increased magmatism at upwelling mantle plumes responsible for ridge volcanism could create anomalous seafloor volcanism, like that observed at ~31 Ma. Alternatively, at ~31 Ma, the Tristan hotspot, responsible for the formation of nearby Walvis Ridge, was located ~800 km south of the ridge segment in this study area. Ridge volcanism in the study area could have been influenced by the nearby presence of the hot spot, leading to the anomalous increase in seafloor volcanic activity.