Samples of moon rocks and regolith collected during the Apollo Missions as well as the lunar meteorites discovered on Earth allow us to study the origin and geology of the Moon directly. The most striking lunar features, clearly visible in the night sky are the large mare basins that formed when a rogue population of asteroids struck the Moon about 3.9 billion yars ago. We are using the chemistry of lunar impact melt rocks, in particular the concentrations of the highly siderophile platinum-group elements, to determine the types of asteroids that created these large (300-2500 km diameter) impact basins. This in turn will tell us about the types of planetesimals traversing the inner solar system at that time, and likely hit the Earth as well. This is largely a laboratory based project (no field work planned right now) and requires a person who wants to learn leading-edge chemical techniques, is a good observer with excellent attention to detail, and thinks big picture. This is just one of many potential projects working on lunar samples. Contact us for more information.

Lunar soils carry a remarkable record of volcanic eruptions and meteorite impacts that occurred on the Moon over the past four billion years. These events can be studied by analysing small fragments of volcanic and impact glass found in the lunar soils. For this project you will measure 39Ar-40Ar ages and chemical compositions of individual glass beads from lunar regolith collected at each of the six Apollo landing sites. This will allow us to distinguish volcanic from impact events and evaluate the efficiency of sediment transport on the Moon. This project will position you well to participate in the upcoming decade of international space exploration and resource utilisation on the Moon and Mars. The project will suit someone with an interest in planetary science, a good knowledge of basic geochemistry, and a steady hand. The image shows a picture of moon rock 67016. It is an impact breccia that was collected at the Apollo 16 landing site. Contact Marc.Norman@anu.edu.au for further information.

Cratonic lithosphere underlies ancient, geologically stable regions of the earth’s continental crust. Because it is the ultimate source of most diamonds, it is of economic significance. It is also of great scientific significance as it contains a time-integrated record of important tectonic and geological events such as the formation and destruction of cratons the growth and dissolution of diamonds, depletion and refertilisation of the lithosphere, and metasomatic enrichment which may be associated with kimberlitic or other alkaline magmatism.

These projects will examine suites of xenoliths, which are fragments of the cratonic lithosphere from a variety of localities. They are variably metasomatised garnet peridotites and MARID (mica-amphibole-rutile-ilmenite-diopside) and related xenoliths. The aims of the projects are to unravel the geological histories of the samples, in particular their metasomatism, using detailed petrographic investigations, and mineral chemistry determined by electron microscopy, laser ablation-ICP-MS and radiogenic isotope analysis. Innovative techniques such as the electron microprobe based FLANK method and Mössbauer Spectroscopy will be used to determine the lithospheric pressure, temperature and redox conditions recorded by the xenoliths and how they vary with different metasomatic styles and intensities, as these may be important controls on diamond growth or dissolution in the deep cratonic lithosphere.

The student may be involved in fieldwork to collect new samples, and there may also be opportunities to use Proton-Induced-X-ray-Emission spectroscopy (PIXE) or synchrotron-based X-ray absorption spectroscopic (XAS) techniques for mapping trace element distributions in mineral grains.

There is now general acceptance of the concept that the earth’s mantle is chemically and isotopically heterogeneous on a variety of scales and that much of this heterogeneity relates to reintroduction of crustal material into the mantle via subduction. Recycled oceanic lithosphere may be subducted deep into the convecting mantle and eventually entrained in upwelling mantle where it may melt and contribute components to lavas erupted in a variety of tectonic settings. For example, an important recent contribution (Sobolev et al. 2007, Science 316, 412-417) claims on the basis of minor elements in olivines crystallised from primitive magmas, that the magmas’ source regions contained garnet orthopyroxenite, itself a reaction product between normal mantle peridotite (lherzolite or harzburgite) and partial melts of deeply recycled oceanic crust (eclogite). This project aims to test this model by performing high pressure melting experiments on garnet orthopyroxenite, and analysing run products by electronprobe microanalysis or by laser ablation – ICPMS. The summer student would be involved in performing the high-pressure experiments on the RSES’ piston-cylinder presses and sophisticated microbeam analysis of the run products. This data can then be used to test models invoking involvement of recycled oceanic crust in magma genesis.

Whether the earth’s mantle is oxidising or reducing is of particular importance, because its oxidation state partially controls the nature of fluids present there. For example, in a reduced mantle, fluids may be methane + water – dominated, but in a more oxidised mantle they may be carbon dioxide + water dominated. Trace or minor amounts of fluid in the mantle exert a profound influence on the way the mantle partially melts to produce magma and consequently on the nature of the magmas produced and erupted or emplaced into the crust. It is possible to determine the oxidation state of the mantle from fragments of lithospheric material (garnet peridotite xenoliths) transported to the surface in some volcanic eruptions. However, this requires precise measurement of Fe3+/total Fe in the mineral garnet, and this is currently difficult using conventional microbeam analytical techniques. We are endeavouring to develop a new synchrotron-based technique called Fe K-edge XANES. This requires a series of well-characterised garnet samples for calibration, and the summer student involved in this project would be engaged in synthesising them using high pressure experimental equipment at RSES, and in the full characterisation of the experimental materials using sophisticated analytical techniques such as electronprobe microanalysis and X-ray diffraction. Subsequent involvement in synchrotron measurements may also be possible.

One effect of alteration of the basaltic ocean floor is addition of a few weight % carbonate in the form of calcite, or CaCO3 to the upper few 100 metres of the oceanic crust. There is abundant evidence from high pressure experimental studies and from investigations of high pressure and ultra-high pressure metamorphic rocks that some of this carbonate can survive the subduction process and is recycled back into the deeper mantle. Geochemical evidence suggests that this material may then be important in some partial melting processes in the upper mantle, leading to formation of certain types of magmas (eg some alkali basalts, carbonatites, kimberlites etc). The recycling of carbonate from the earth's atmosphere, hydrosphere and crust, back into the mantle is thus likely to be a highly significant part of the planet's overall carbon cycle, with an important role to play in the chemical evolution of the earth. However, relatively little is known about the behaviour of carbonate-bearing mafic rocks at high pressure (i.e. carbonate eclogite) and the few studies that have been done have yielded contrasting results. The aim of this project is to use high pressure experimental petrology to carefully constrain the high pressure melting and phase relations of carbonate eclogite, and to develop models for its involvement in upper mantle petrogenesis. The data produced will also enable calibration of a geobarometer that could be used to determine the barometric history of natural crustal high pressure carbonate + garnet assemblages. The student would be involved in a larger ARC funded project investigating the melting behaviour of heterogeneous upper mantle. He/She would prepare high pressure experimental assemblies, run them in the high pressure experimental equipment at RSES and undertake microanalysis by electron microprobe and laser ablation ICPMS. There are also possibilities for field work aimed a collecting suitable samples for thermobarometry based on garnet-carbonate exchange equilibria. The student would be closely involved in analysis and interpretation of the experimental and natural samples.