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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Sally Gibson, Earth Sciences

Co-Supervisors: Simon Passey, CASP, Cambridge, UK; Ben Black, CUNY, USA and Dereje Ayalew, Addis Abba, Ethiopia

This is a CASE project with CASP

Brief summary: 
This project seeks to quantify the amount and also constrain the source of volatiles emitted during the rapid eruption of enormous volumes of flood basalt lavas in Large Igneous Provinces (LIPs), which have climatic consequences and have been linked with mass extinction events.
Importance of the area of research concerned: 
The rapid eruption of enormous volumes of flood basalt lavas in Large Igneous Provinces (LIPs) is responsible for dramatic increases in the concentrations of atmospheric volatiles. Among these magmatic gases, carbon dioxide (CO2) is particularly vital to the life cycle of LIP magmatism and its climatic consequences, which have been associated with major mass extinction events. Sudden atmospheric injections of volcanic sulfur, chlorine and fluorine also significantly impact on the habitability of our planet. Nevertheless, concentrations of volatiles in LIP magmas themselves are poorly constrained, mainly because of difficulties obtaining high-precision analyses of volatile elements from quenched glasses. One of the best modern-day analogues for LIP formation and evolution is the East African Rift, where volcanic outgassing of high levels of CO2 and halogens by rift related volcanoes is notorious. Little is known, however, about how the mantle and crustal origins of these volcanic emissions, and their effects on surface systems, have varied since the impact of the proto-Afar mantle plume and formation of the Ethiopian LIP in the northern East African Rift at 30 Ma.
Project summary : 
While it widely acknowledged that LIPs play an important role in global volatile cycles (Black & Gibson, 2019) the most reliable data, from the Siberian and Deccan Traps, have yielded a wide range of volatile concentrations (e.g. Hernandez Nava et al., 2021). It is unclear as to how these might: (i) be affected by degassing; and (ii) vary within individual LIPs. The young, fresh nature of lavas in the Ethiopian LIP, together with their well-exposed stratigraphy, availability of high precision Ar/Ar dates, and large xenolith cargo offers a unique insight into how volatiles are sourced and emitted during our planet’s largest volcanic events. The project will examine the role and atmospheric impact of volatiles in the major pulse of tholeiitic flood lavas and mildly-alkaline shield volcanoes in the Ethiopian LIP and how these have varied through to modern day rift volcanism.
What will the student do?: 
Establishing accurate concentrations of volatiles in flood basalt lavas requires a systematic petrological and geochemical investigation. The student will undertake at least one field season with CASP in Ethiopia. Here, the dissected terrain shows the full stratigraphic succession through the lava pile with the earliest lavas overlying organic shales and sandstones. Specific target locations will be: (i) fine grained basalts/scoria containing olivine and clinopyroxene phenocrysts; (ii) lava-sediment interactions. The student will also collect mantle and crustal xenoliths. Such mantle samples are rare in flood basalt provinces and offer a unique insight into the volatile composition of the underlying lithospheric mantle (Gibson et al., 2020). Both melt inclusions and mineral phases will be analysed for major and trace elements and a subset for volatiles, generating the first data set of volatiles in the Ethiopian Traps and the underlying mantle. The dataset will be used in numerical models of mantle melting and crystal fractionation to compare the role of volatiles in flood basalt magmas in the East African Rift with the Deccan and Siberian Traps, and input into climate models.
References - references should provide further reading about the project: 
Black B. A. and Gibson S. A. (2019) Deep carbon and the life cycle of Large Igneous Provinces. Elements 15, 319–324.
Gibson S. A., Rooks E., Day J. A., Petrone C. M. and Leat P. T. (2020) The role of sub-continental mantle as both “sink” and “source” in deep Earth volatile cycles. Geochimica et Cosmochimica Acta, 140–162.
Hernandez Nava A., Black B. A., Gibson S. A., Bodnar R. J., Renne P. R. and Vanderkluysen L. (2021) Reconciling early Deccan Traps CO2 outgassing and pre-KPB global climate. PNAS 118.
You can find out about applying for this project on the Department of Earth Sciences page.
Prof Sally Gibson
Department of Earth Sciences Graduate Administrator