AbstractCorbetti caldera is a Quaternary volcanic complex in the southern sector of the Main Ethiopian Rift. There is little published work on this volcanic complex and its volcanic history is poorly constrained. However, Corbetti caldera has recently shown to undergo active deformation (Biggs et al.(2011)) and this event encouraged a deeper knowledge of its volcanic behaviour in order to improve the volcanic risk assessment of the area.
This work aims at understanding the volcanic history of Corbetti caldera by the combination of stratigraphic and geochemical investigations. New 40Ar/39Ar dating analyses have been also carried out on two of the main eruptions from both the syn and post caldera activity. The stratigraphic reconstruction, based on the Unconformity Bounded Stratigraphic Units method (UBSU, Salvador (1987)) as modified for the volcanic terrains by De Rita et al. (1997), revealed a complex eruptive history characterized by two eruptive epochs and four eruptive units. The concept of lithosome (Giordano et al. (2006), Fusillo et al.(2015)) has been also applied and four lithosomes have been identified (Corbetti Composite Lithosome, Urji lithosome, Danshe lithosome and Chabbi Composite Lithosome). Corbetti caldera shows a compositional gap, typical of bimodal magmatism as found elsewhere in the Ethiopian Rift (Alutu, Gedemsa, Boseti, Fantale). A petrogenesis of protracted fractional crystallization from alkali-basalt is hypothesized for most of the Quaternary calderas along the rift and the same model might be also applied to Corbetti magmatic system. The sampling and geochemical analyses for the first time of a basaltic deposit from the post-caldera activity of Corbetti, along with the new geochemical analyses of the rhyolites, allowed a comparison with the products of the Quaternary calderas of Alutu, Gedemsa, Boseti, Fantale, for a more comprehensive understanding of Corbetti volcanic history.
|Date of Award||25 Sep 2018|
|Supervisor||Richard A Brooker (Supervisor) & Jon Blundy (Supervisor)|