Norman H. Sleep

Cenozoic magmatism throughout east Africa resulting from impact of a single plume

The geology of northern and central Africa is characterized by broad plateaux, narrower swells and volcanism occurring from ∼45 Myr ago to the present. The greatest magma volumes occur on the >1,000-km-wide Ethiopian and east African plateaux, which are transected by the Red Sea, Gulf of Aden and east African rift systems, active since the late Oligocene epoch. Evidence for one or more mantle plumes having impinged beneath the plateaux comes from the dynamic compensation inferred from gravity studies, the generally small degrees of extension observed and the geochemistry of voluminous eruptive products. Here we present a model of a single large plume impinging beneath the Ethiopian plateau that takes into account lateral flow and ponding of plume material in pre-existing zones of lithospheric thinning. We show that this single plume can explain the distribution and timing of magmatism and uplift throughout east Africa. The thin lithosphere beneath the Mesozoic–Palaeogene rifts and passive margins of Africa and Arabia guides the lateral flow of plume material west to the Cameroon volcanic line and south to the Comoros Islands. Our results demonstrate the strong control that the lithosphere exerts on the spatial distribution of plume-related melting and magmatism.

Hydrothermal Circulation and Geochemical Flux at Mid-Ocean Ridges

The flow rate of sea water through sub-sea-floor hydrothermal systems at mid-ocean ridges has been estimated at

Archean Plate Tectonics: Constraints and Inferences

1.3-9 \times 10^{17} g/yr

No climate paradox under the faint early Sun

by consideration of the rate at which circulating fluid must advect heat out of the spreading plates into the oceans. The rate of hydrothermal heat advection was obtained by computing the difference (

Lateral flow of hot plume material ponded at sublithospheric depths

40 \pm 4 \times 10^{18} cal/yr

Application of a unified rate and state friction theory to the mechanics of fault zones with strain localization

) between the theoretical heat production associated with sea-floor spreading and observed heat flow measurements. Effects of exothermic chemical reactions, direct heat loss from flows extruded on the ocean floor, and heat of crystallization of basalt were minor and yielded insignificant contributions to the estimate. The majority of dredged ocean-floor metamorphic rocks appear to represent the products of intensive hydrothermal reaction with hot sea water. The chemical trends (loss of Ca and K, gain of Mg, Na, and