Containerless heating for extreme melts and glasses: determining the melting temperature of the lower mantle.

Containerless heating is an increasingly important tool for studying liquids at extreme temperatures and for synthesising extreme compositions of glass. For example, neutron and X-ray diffraction studies of the structure of molten refractory materials (e.g. Al2O3) have used levitation furnaces to suspend molten drops in gas at temperatures of over 2500 K1. Containerless heating has the following advantages: - the maximum temperature is not limited by the crucible material - there is little chance of contamination of the sample - the entire surface of the melt is in contact with the carrier gas, leading to rapid equilibration and inhibition of crystallisation during quenching. Within the Earth Sciences, this means that studies of fractionation can be performed at extreme temperatures relevant to planetary accretion and impact processes, and extremely silica-poor glasses (e.g. pure olivine) produced at controlled oxygen fugacity. However, no such facility exists in the UK Earth Sciences community. We propose to develop a laser-heated gas-levitation furnace which fulfils all of the aspects mentioned above. Within the remit of this small-grant proposal we will use it for synthesis of peridotite glass compositions for studies of lower-mantle melting and of the effect of pressure on peridotitic melt structure. Future studies using the levetation furnace developed here will include isotopic fractionation at extreme temperatures and the evolution of the Earth's bulk composition during accretion, for which funding will be applied for separately.