The volcanic and geochemical evolution of the Adda’do Magmatic Segment, Southern Afar, Ethiopia

Abstract

The evolution of continental rifting to seafloor spreading is a key part in the cycle of plate tectonics on Earth. Magmatism and volcanism become increasingly common as continental rifts evolve and mature, but our current understanding of how these processes change and evolve in such environments are still limited. As the world’s longest and best-exposed example of a continental rift, the East African Rift System (EARS) is an ideal natural laboratory to study along-rift variations in the style and characteristics of magmatism in an active continental rift. The EARS showcases a range of different rifting styles along its length, making it possible to study a range of factors that may result in along-rift variations in the nature and intensity of magmatism in active rift zones. In this thesis, the volcanic and geochemical characteristics and evolution of three volcanoes, Ayelu, Abida and Yangudi, which together form the Adda’do Magmatic Segment (AMS) in southernmost Afar, is characterised using a combination of remote sensing mapping, petrography, alongside major element, trace element and radiogenic isotope geochemistry.

Results from remote sensing mapping and cross-cutting relationships of rock units in conjunction with major element geochemical data show that all three AMS volcanoes exhibit similar evolutionary pathways, exhibiting at least three cycles of mafic-to-felsic evolution in the southern AMS. Modelling of trace element and Pb-Sr-Nd isotope data suggest that the main mantle source contribution in the AMS is the Afar plume, with minor contributions from an EM1-like source and variable contributions from a depleted mantle source. Using Pb-Sr-Nd and trace element data, a model for magma storage and pathways from mantle source to eruption in the AMS is presented. I find isotopic evidence for increased crustal contamination at Ayelu and Abida relative to Yangudi, which is likely linked to along-rift variations in crustal thicknesses and rift evolution.

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Identifiers

ORCID for Thomas Gernon: orcid.org/0000-0002-7717-2092

ORCID for Derek Keir: orcid.org/0000-0001-8787-8446

ORCID for Dr Rex Taylor: orcid.org/0000-0002-9367-0294

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