The 130 Ma Geochemical Evolution of the Tristan-Gough Hotspot Track: The Life Cycle of a Zoned Plume

The Tristan-Gough volcanic track in the SE Atlantic represents a classic hotspot track. It extends from the Etendeka flood basalt province in southern Africa southwestwards along the Walvis Ridge and then Guyot Province to the volcanically-active Tristan da Cunha and Gough island groups. Both the age of the erupted volcanic rocks (~132 to 70 Ma old). The data for the available samples fall within the enriched Gough field defined by the ≤70 Ma old part of the hotspot track. The Parana flood basalts also have compositions similar to the Gough subtrack rocks and the Etendeka to the Tristan subtrack rocks in the ≤70 Ma old part of the hotspot track. These data suggest that the plume head contained both components and that they may have been spatially separated with Tristan to the east and Gough to the west. During the early plume tail phase (~115-70 Ma), there is no evidence for the presence of the Tristan component, but only the enriched Gough component was identified– suggesting that only the enriched “LLSVP or superplume” source was tapped by the plume. As the plume became weaker, surrounding depleted mantle was entrained on the NW side of the plume beginning at ~70 Ma. This entrainment has led to zonation of the plume. Interestingly shortly after chemical zonation appeared in the Walvis Ridge (i.e. plume conduit), the hotspot track bifurcates forming two morphologically and geochemically distinct tracks, which have continued to diverge over the last 70 Ma until the present with ~400 km between Tristan and Gough Island groups at the present. Possible mechanisms for the cause of the geochemical zonation, e.g. plume-splitting and the formation of a viscous plug causing separation of plume material, are under investigation