Isotope Fractionations during volatile loss from Planets and Asteroids

The rocky bodies in the inner Solar System are known to be depleted in moderately volatile elements compared to CI chondritic meteorites, the main building blocks of the planets and moons. The volatile content of these bodies was governed by the mixing of volatile rich CI chondritic material and a volatile-poor material. Recent work by Norris and Wood (2017) has shown that volatile element abundances in the silicate Earth correlate well with the volatility of those elements in a siliceous system, suggesting that the Earth's volatile element budget may be explained by vaporization and devolatilization during early Earth forming events. This challenges the conventional hypothesis that these element depletions can be explained by incorporation of these elements in the core. If volatility is the main cause of element depletions, we should be able to observe this process by looking at isotope fractionation.

Our aim for this project is to test the devolatilization hypothesis by investigating the effects of devolatilization on the isotopic composition of several elements. We will look at elements with varying degrees of volatility and depletion in the silicate Earth compared to CI chondritic material, starting with Zn and Cd and progressing to Cu and Pb. We will focus on these as variations in isotopic composition for these elements are known for the Earth, Mars, Vesta and various meteorite classes.

We will test our hypothesis in the lab by performing relatively short (60 minute) experiments in a furnace at high temperature, in a heavily reducing environment at atmospheric pressure on rock powders that have been doped with trace elements. The samples are doped in the studied elements to ensure we are able to measure them accurately after the experiments. The resulting run products will be analysed for both elemental and isotopic abundances. By comparing the results from the experiments with available data for the Earth, Moon, Mars and meteorites we will be able to test the initially proposed model of devolatilization and further advance models describing the early evolution of the Earth's volatile budget.

This project is a part of the Science and Technology Facilities Council (STFC)'s Astronomy and Space Science Research, specifically focused within Science Challenge B: 'How do stars and planetary systems develop and is life unique to our planet?'. This project will be performed under the supervision of Professor B.J. (Bernard) Wood and Dr. J. (Jane) Barling from the Department of Earth Sciences at the University of Oxford.

[1] Norris, C.A., Wood, B.J. (2007). Earth's volatile contents established by melting and vaporization. Nature, vol. 549, p. 507-510