Ethiopian Flood Basalts
objectives
This project primarily focused on the large volume of 'flood basalts' that erupted on the northwest Ethiopian Plateau. These rocks are so-called because they tend to form via the relatively rapid extrusion of vast volumes of basalt magma. These basalt flows stack one upon another and so provide a temporal record of what was going on in the magma chamber and also in the region in the mantle where they were initially created.
field work
This project was largely completed in four field seasons and consisted of a complete collection of basalts from the very bottom where they contact the old Pan-African aged granite, to the very top where younger flows overly the ca. 30 million year old flood basalts. The field work resulted in many hundreds of kilograms being shipped back to Michigan for further geochemical testing.
discoveries
We have presented the first detailed petrographic stratigraphy of a flood basalt from top to bottom. We have also identified the presence of an exotic source to magma creation in the region that has implications for understanding magma generation from Egypt to Arabia and down the East African Rift.
ongoing work
We are continuing to probe how the magma chamber that fed these massive flows worked. How often did an eruption happen, how much material was feeding into it? We are also exploring how the magma was created in the first instance. There is a view that these magmas may be derived from the African Superplume - a jet of material that rose from near the Earth's core and impacted the underside of the African continent.
ABSTRACTS
1. Rooney, T.O., Dosso, L., and Nelson, W., 2010. Recognition of a HIMU-like reservoir beneath northwest Ethiopia. Geochimica et Cosmochimica Acta. v. 74, p. A881.
2. Rooney, T.O., Nelson, W., and Dosso, L., 2011. Metasomatic enrichment of the lithosphere-asthenosphere boundary: A key processes in extensional environments? EarthScope Institute on the Lithosphere-Asthenosphere Boundary. Portland, OR, September 19-21.
3. Rooney T.O., Nelson W., Dosso L., Furman T., and Hanan B., 2014. HIMU-Like Magmatism on the Northeast African and Arabian Plates: The Role of Continental Lithosphere Metasomes. Goldschmidt Abstracts, 2014-2113
4. Rooney, T.O., Nelson, W.R., Ayalew, D., Yirgu, G., Herzberg, C., and Hanan, B., 2014. An olivine-free mantle lithology as a source for mantle-derived magmas: the role of metasomes in the Ethiopian-Arabian large igneous province. Abstract DI21A-4263. Presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 December.
5. *Trestrail, K.R., and Rooney, T.O., 2014. Lithospheric mantle deformation in the Yerer-Tullu Wellel Volcanotectonic Lineament: A study of peridotite xenoliths. Abstract T43A-4693. Presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 December.
6. *Krans, S., Rooney, T.O., Yirgu, G., Ayalew, D., 2014. A top to bottom stratigraphic investigation of two transects through the Ethiopian flood basalt province. Abstract DI43A-4362. Presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 December.
7. Rooney, T.O., Bradley, B.*, Krans, S., Kappelman, J., Ayalew, D., Yirgu, 2015. Diary of a flood basalt: A stratigraphic tour of two sections within the Oligocene Ethiopian Traps. Abstract V41C-3080. Presented at 2015 Fall Meeting, AGU, San Francisco, Calif., 14-18 December.
8. Rooney, T.O., Flood Basalts and Pulsed Magmatism in East Africa. Abstract 833. Presented the Meeting of the International Association of Volcanology and chemistry of the Earth’s Interior, Portland, Oregon, United States. August 14-18 2017.
9. *Krans, S., Rooney, T.O., Kappelman, J., Yirgu, G., Ayalew, D., 2017. Life and Death of a Flood Basalt: Evolution of a Magma Plumbing System in the Ethiopian Low-Ti Flood Basalt Province. Abstract V33I-07. Presented at 2017 Fall Meeting, AGU, New Orelans, LA., 11-15 December.