Regularities of Variations in the Composition of Plume-Related Volcanic Rocks in the South Atlantic and on the African Plate

Abstract

The paper demonstrates the distinct difference between plume volcanism on oceanic and continental plates. A specific characteristic inherent solely to a continental setting is the generation of ultramafic alkali melts of the kimberlite–melilitite–carbonatite series, which has recurred many times in Earth’s history. The main cause of the different types of volcanism in the South Atlantic and Africa was the accumulation of C, H, F, K, Na, and other elements at the base of the subcontinental lithosphere under the influence of the African superplume. Alkali and volatile components to not accumulate on an oceanic plate. The interaction of alkali–carbonate fluids with mantle peridotites under the very thick continental plate led to their metasomatic transformation and the melting of low-silicate CO₂-saturated magmas in hypogene conditions and basalt magmas even more enriched in silica at smaller depths. The melting of hypogene melts of the kimberlite–melilitite–carbonatite family anomalously enriched in REE impurities is controlled by the CO₂ pressure regime. The composition of basalt melts significantly depends on the tectonic formation conditions.