Mare Basalt Synthesis

The Moon represents the only example of a satellite body in The Solar System even remotely comparable in size to its host planet. Phobos and Deimos (the moons orbiting Mars) are both several orders of magnitude less massive than Mars itself, compared with approximately two orders of magnitude separating the mass of the Earth and the Moon (Burns 1992). This precludes research on our moon by analogy. Current theory suggests that the Moon is formed from an assembly of debris ejected from the earth beyond the Roche radius, the result of a massive impactor. Simulations of an off centre impactor can produce an iron poor Moon with the correct angular momentum for the Earth-Moon system. These successful simulations either require a great reduction in angular momentum after the impact or significantly more mass to be added to both bodies following the impact event (Canup Asphaug 2001).

The Apollo missions provided the critical constraints on the nature of the surface lithologies and how the thermal and chemical structure of the Moon has evolved. These observations can be briefly summarised:
1) Maria are impact basins filled with basaltic lava with a negative Europium anomaly that date from 3.1-3.9 Ga
2) Terra are old (>3.9Ga) and very rich in feldspar
3) Strong depletion in siderophile and volatile elements relative to earth is complicated by an enrichment in very volatile elements such as Te
4) Co, a siderophile, is enriched
5) Relative enrichment in refractory elements
6) Small core about 3wt% of Moon and 350 km radius
(Shearer et al 2006)

Trace elements have very limited influence on macroscopic processes and can therefore be used as reliable geological time-scale markers. As an example, Hafnium Tungsten isotopes have been widely used to inform debate on the timing of core formation (Touboul et al 2007).

I aim to further develop partitioning data on a number of trace elements present at several lunar reservoir sites. This will enable the development of an effectively parameterised crystallisation model at chemical conditions relevant to mare basalt genesis, and will enhance existing Moon formation simulations. This data can then be used to enhance crystallisation models such as those used in the MELTS package.

This project will investigate two key questions:

1) Was the Co anomaly found in lunar precursor material or did it result from unique lunar conditions, if due to unique crystal phase when and where did this happen?
2) Is the enrichment of the moon in extremely volatile elements such as Te soluble for existing models?