Magmatism and continental rifting during the opening of the South Atlantic Ocean: a consequence of Lower Cretaceous super-plume activity?

Abstract

Abstract Two large-scale mantle plumes, whose present-day foci are close to the oceanic islands of Tristan da Cunha and St Helena, appear to have played a significant role in the initial stages of rifting between Africa and South America during the Early Cretaceous opening of the South Atlantic Ocean. They may represent the initial burst of a super-plume event which generated extensive oceanic plateaux in the Pacific and Indian oceans. The recent volcanic products of Tristan da Cunha and St Helena have near endmember Sr-Nd-Pb isotopic characteristics (EM I and HIMU) in the spectrum of ocean basalt isotopic compositions. These isotopic signatures are recognised for more than 100 Ma in the plume-related magmatic products and therefore appear to be a long-lived feature of the plume source. The history of rifting and magmatism in West and Central Africa/NE Brazil and in southern Brazil, above the broad heads of the initial starting plumes between 145 Ma and 130 Ma, strongly suggests that there are different physical differences between the two plumes in addition to chemical ones. The St Helena plume appears to have been much weaker and cooler, with a smaller buoyancy flux. The hotter Tristan plume has generated voluminous flood basalts volcanism in the Paraná basin of Brazil and appears to be associated with continental break-up within a few million years of the plume head impinging on the base of the lithosphere. In contrast, in West and Central Africa, rifting above the St Helena plume, associated with small volumes of alkaline-transitional magmatism, spans an extended period of 30–40 Ma before break-up occurs in the Equatorial Atlantic.