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The central Kenya peralkaline province: a unique assemblage of magmatic systems

R. Macdonald^1,2,* and B. Bagiski¹

¹ IGMiP Faculty of Geology, University of Warsaw, al. wirki i Wigury 93, 02-089 Warsaw, Poland
² Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK

^* E-mail: r.macdonald{at}lancaster.ac.uk

The review focuses on the evolution of five contiguous peralkaline salic complexes in the south-central Kenya Rift Valley, stressing new developments of general significance to peralkaline magmatism. The complexes have evolved dominantly by combinations of fractional crystallization and magma mixing; volatile-melt interactions, remobilization of plutonic rocks and crystal mushes, and carbonate-silicate liquid immiscibility have been additional petrogenetic processes. Geochemical and experimental studies have shown that pantelleritic magmas can be generated by fractional crystallization of trachyte and high-silica rhyolite. Melts of comenditic composition were also formed by fractionation of trachyte but also locally by partial melting of syenites. Studies of apparent partition coefficients have provided some of the first data on element distribution between phenocrysts and peralkaline silicic melts. Compositional zonation has been ubiquitous in the complexes, probably a result of the very low viscosity of the magmas.

KEYWORDS: Kenya Rift, peralkaline salic rocks, petrogenesis, plumbing systems