Volatiles and their sources in the Afro-Arabian LIP

The eruptions of Large Igneous Provinces (LIPs) are strongly correlated with mass and minor extinction events, which in turn are driven by complex short-term sulphur mode cooling and long-term carbon mode warming from volatile outgassing (Black et al, 2018). The Afro-Arabian LIP (30Ma) has been implicated in cooling and faunal turnover at the Oligo-Miocene boundary, though in order to assess these correlations, pre-eruptive volatile contents must be constrained for the main stages of LIP volcanism. In Ethiopia, this volcanism exhibits a transition from compositionally zoned tholeiitic flood basalts in the Oligocene to alkaline shield volcanoes in the Miocene. These lavas sample a heterogenous mantle enriched in volatiles via metasomatic agents derived from a) the Afar Plume, b) slab components from the Pan-African subduction event 600-700Ma and c) carbonatitic fluids, related to either ancient subduction events or recent plume activity (Nelson et al, 2016; Rooney et al, 2017).

We investigate a series of lavas in the NW Ethiopian Plateau across the flood-shield transition using whole rock, phenocryst, and preliminary melt inclusion data, in order to examine magma sources and volatile contents, and how these change over time. Trace element signatures differ between flood basalts and shield volcanoes, reflecting different mantle sources and depths of magma generation. To further corroborate this, we present new constraints on pressure and temperature using cpx-liquid thermobarometry. We additionally present early estimates of pre-eruptive volatile contents using a range of proxy methods, including ol-liquid hygrometry, the FeO-S proxy for sulphur, and the CO₂-S proxy for CO₂, and discuss how these compare to our EPMA pilot study on MI volatile contents. Future work will involve extensive EPMA and SIMS to perform volatile and trace element analysis in melt inclusions in order to constrain the full suite of magmatic volatiles (CO₂, H₂O, S, F, Cl) in the spatially and temporally variable lavas of the Afro-Arabian LIP.