Collecting and Melting: Meteorites from the Nullarbor and Icy Planets

Andrew Langendam, School of Earth, Atmosphere and Environment

Wed 4th February 12 – 1 pm Rm 312.222

For the past seven years, the Monash Meteorites Group has been conducting field expeditions to the Eastern Nullarbor in search of meteorites. Our search technique, a non-traditional one, has been developed to locate strewn fields with some success. In addition, we have investigated how core formation occurs beyond the protoplanetary snowline. Here, planetesimals accrete with water ice which oxidised metal phases to magnetite. This excludes Fe-FeS based core formation from these bodies, and hence core formation as we know it. We acquired a 5.9g sample of the Karoonda CK4 chondrite form the South Australia Museum. This was divided into 12 pellets, and heated in a 1 bar Ar atmosphere furnace at temperature increments of 50°C between 900 and 1300°C. Our experiments show that at all temperature increments investigated, a silicate wetting Fe-S-O melt is generated. Below 1150°C the Fe-S-O melt / silicate melt ratio is high enough that Fe-S-O melt forms connected networks allowing rapid migration via percolative flow. Above 1150°C Fe-S-O tends to form spherical droplets that get trapped in larger silicate melt pockets between unmelted olivine and pyroxene. Thus, unexpectedly, core formation is easier and occurs at lower temperatures in oxidised bodies. Cores form through the percolation of Fe-S-O melt through an interconnected network until the silicate melt to Fe-S-O ratio inhibits the connectivity of Fe-S-O melt. Previous studies have shown that increased O in Fe melts increases their conductivity, hence a magnetic fields generated by a Fe-S-O core could be comparable to those produced by metallic cores. These results also provide a basis for more accurate models of the interior of the icy moons in our solar system, and better understand the processes generating weak magnetic fields in these moons.