Eruptive history and magmatic evolution at Corbetti Caldera, Ethiopia

The East African Rift (EAR) is the type example of a continental rift system associated with active volcanism.One segment of the EAR, the Main Ethiopian Rift (MER), is of interest due to the abundance of Quaternary volcanism focused around large silicic centres. Almost 50% of Ethiopia's population live within 100 km of one of its 65 volcanoes however,our understanding of the recent volcanic history of the region is considerably lacking.Recent attempts to improve our understanding
of the region have yielded important findings better constraining the frequency and magnitude of past eruptions and the magmatic processes that have fed volcanism over the last 300 ka.Understanding volcanism in this region is of growing importance due to the potential of utilising volcanic centres as a source of geothermal energy.Corbetti caldera is the southernmost, and one of the largest volcanic calderas within the MER.Recent studies have identified multiple high magnitude events emanating from 3 post caldera edifices(Urji, Artu and Chabbi) and demonstrated continued restlessness over the past 10 years. Whilst timings of eruptions over the last 10,000 years have been proposed, they are still relatively poorly
constrained in terms of timing, magnitude and dynamics. Some work has been carried out on the ~2 ka BP Wendo Koshe Younger Pumice unit, a pumiceous horizons thought to be sourced from Urji,characterising its dynamics and extent.However, no such work has been done on any other deposits within the complex. One reason for this is that most deposits from Corbetti are both geochemically and visually homogenous, making distinguishing between them challenging. One way to tackle this problem is by using trace element analysis to aid correlation between proximal and distal deposits and to investigate magmatic processes. Whilst some authors have conducted trace element analysis, a significantly larger dataset is required to catalogue eruptive events. In addition, the controls on effusive and explosive volcanism is one of the key areas of investigation in volcanology.Corbetti provides an ideal place to study this as Urji and Chabbi exhibit almost exclusively explosive and effusive eruptions respectively. One feature that is consistent across all volcanoes within the MER is their strong peralkalkinity. The evolution of peralkaline magmas has been debated within scientific literature,
however, a consensus has arisen that these alkaline magmas predominantly evolve through extreme fractional crystallisation which may be slightly influenced by crustal assimilation. This has been the process attributed at several volcanoes within the MER, however all these volcanoes have deposits that have a crystal cargo and display a wider range in erupted compositions. Corbetti is somewhat unique in that most eruptive deposits are completely aphyric which may indicate additional processes may be influencing magma evolution or melt extraction.