Magmatic degassing of moderately volatile elements: Implications for the Earth’s volatile budget

Theme: Solid Earth Dynamics

Primary Supervisor:

Eleanor Jennings

Department of Earth and Planetary Sciences, BBK

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Secondary Supervisor:

Christina Manning

Department of Earth Sciences, RHUL

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Project Description:

There is much debate about the Earth’s initial volatile budget, and whether its volatile depletion relative to chondrites is a result of just condensation in the protoplanetary disk (and volatile loss to the core), or if impact-driven magma ocean formation and degassing were important. The concentrations of major volatile elements in the Earth’s mantle and core are poorly constrained. However, the concentrations of moderately volatile (MV) elements (e.g. Ag, As, Bi, Cd, Ge, In, Pb, Sn, Zn) are better constrained, and act as a proxy for the origin of the Earth’s volatile element budget. The magmatic degassing behaviour of these elements is not well understood: it has been studied in laboratory experiments, but degassing systematics in experiments are likely to be different to natural systems as the major volatile species and gas phase speciation will be a controlling factor.

This project will examine magmatic degassing in modern volcanic settings to determine its impact during the Earth’s accretion. Some moderately volatile elements are highly toxic and are present in volcanic plumes in significant quantity, so understanding their degassing behaviour for environment/health is a secondary project motivation. The student will work with glassy volcanic products (e.g. melt inclusions; pillow basalt rims; glass lapilli from fire fountains; ash) and analyse a suite of volatile elements by LA-ICP-MS, EPMA, and SIMS, to identify degassing trends. Fractionation through degassing and crystallisation would be considered in order to define relative volatilities of the MV species. This could be supported by published or new gas measurement data.

Policy Impact of Research:

The MV elements arsenic, mercury, and lead, are known to be toxic to life, and are present in volcanic plumes and fallout. Their degassing behaviour is poorly understood: historic eruptions with known environmental impacts are difficult to interpret in terms of toxicity. This study has implications for volcanoes and health.

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