80-Myr history of buoyancy and volcanic fluxes along the trails of the Walvis and St. Helena hotspots (South Atlantic)

Abstract

both parameters by computing volumes along the hotspot tracks. Neither Walvis nor St. Helena show a 'classical' hotspot behavior. We find that two plumes are at the origin of the St. Helena chain. This study also shows a swell associated with the Circe seamount, supporting the existence of a hotspot NW of the St. Helena trail. The variation in swell and volcanic fluxes suggests temporal variability in the plume behavior at time scales of 10-20 m.y. and 5 m.y., which may be related to oscillations and instabilities of the plume conduit, respectively. Cumulative fluxes in the area are largest for Walvis and weakest for Circe, and all are significantly lower than that reported for the Hawai'i hotspot.

Pleistocene volcanism on São Tomé, Gulf of Guinea, West Africa

“…1 m 3 /s for the St. Helena and Walvis hotspots and ca. 5 m 3 /s for Hawaii (Adam et al, 2007). Although the São Tomé magma flux estimates are probably low, it is unlikely that these calculations underestimate the production by a factor of 100e1000.…”

Interactions between hotspots and the Southwest Indian Ridge during the last 90 Ma: Implications on the formation of oceanic plateaus and intra-plate seamounts

“…Thereby, it is widely used in magmatic flux studies on the Hawaiian hotspot of the Pacific as well as the Walvis and St. Helena hotspots of the south Atlantic [8,9,45]. If the Moho is considered as a compensation level and the local isostasy is assumed, the shape of the Moho and the crustal thickness could be calculated from the residual bathymetry.…”

“…These plateaus and seamounts (or seamount chains) substantially reflect the intensity of magmatism and the tracks of hotspots [2,[4][5][6][7], and record the ages, locations and magmatic volume of seamounts created by hotspots. It would be useful to study the time variation and periodicity of the intensity of hotspot activity and the interaction of hotspots, mid-ocean ridges and transform faults [4,5,8,9]. Radioactive dating of rocks can be adopted to determine directly the ages of seamounts, and the thickness of the oceanic crust (layer 2A to layer 3) can be regarded as a first-order measure of the mantle magmatic volume [10].…”

The onset of Walvis Ridge: Plume influence at the continental margin

“…During the hotspot evolution, magma production was generally diminished and not constant. It varied with periods of 10-20 and 5 Ma (Adam et al, 2007;Gallagher and Hawkesworth, 1994).…”