Petrography and geochemistry of the Holocene monogenetic Bayuda Volcanic Field, Sudan: Insights into the magma plumbing system

Abstract

The Bayuda monogenetic volcanic field (BMVF) is an active, understudied Holocene volcanic field located in the great bend of the Nile, Sudan. The BMVF’s location provides an excellent opportunity to study monogenetic volcanism in an African context. Recent studies have shown that monogenetic volcanoes can have more intricate plumbing systems than initially thought. The project sets out to provide a general description and genesis of the BMVF emphasising the plumbing system. Petrography reveals olivine and clinopyroxene as the main phenocryst phases in a groundmass of predominantly plagioclase and subordinate pyroxene and olivine microcrysts. A significant amount of crystals display pronounced disequilibrium textures alongside sector and oscillatory zoning. Major and trace elements indicate that the BMVF is sodic-alkaline, resembling an OIB signature. Melting models that use partitioning coefficients of Zr, Hf and Nb in phenocrysts estimate 2-4% melting of a metasomatised garnet pyroxenite at a depth of ~2.8GPa as the source melt for the BMVF. The isotopic signature suggests mixing of an enriched mantle component (HIMU) and a depleted mantle component (DMM). Textural evidence alongside KD (Fe-Mg) of olivine indicate open system dynamics by revealing separate magma batches with differing times and depths of emplacement. Ni, Ca and Mn content of olivine, furthers the idea of open system dynamics by revealing processes of 1) ‘failed eruptions’, 2) magma mixing and 3) deep-seated fractionation. This project forms part of a growing number of studies that suggest complex plumbing system for monogenetic volcanic fields.