2015: Year in review

The Experimental Petrology group uses a laboratory-based experimental approach combined with field observations to study the Earth, its origin, evolution and mineral wealth.  The group operates a wide range of experimental devices for generating the high temperatures and pressures that are needed to reproduce the natural conditions within the Earth. The equipment includes high temperature furnaces capable of reaching 1800°C, equipped for precise control of oxygen and sulfur fugacities by gas mixing, 11 solid-media piston-cylinder devices for generating pressures to 6 GPa and temperatures in excess of 2000°C, a multi-anvil apparatus for achieving pressures of 26 GPa and a well-equipped hydrothermal  laboratory. In addition the group runs an array of microbeam analytical techniques, including a Cameca SX100 electron microprobe for major element analysis, laser-ablation ICP-MS for trace element and isotopic analysis and FTIR spectroscopy for the determination of H2O, CO2 and other volatile species. The experimental apparatus is supervised and maintained by two Technical Officers who also ensure compliance with occupational safety guidelines. The electron microprobe is also run by a dedicated manager. The laser-ablation laboratory saw a succession of temporary technical operators on an ad-hoc basis before Dr Peter Tollan took charge at the end of the year.

The group in 2015 had 14 PhD students using the high-temperature, high-pressure facilities, plus a number of Honours and two MSc students. Four PhD students graduated during the year.

The group started the year with six continuing academic staff, as defined by those whose activities were centred around the experimental and analytical laboratories run by the group, namely Profs. Arculus, Hermann and O’Neill, and A/Profs. Berry, Mavrogenes and Yaxley, but has been sadly depleted by the loss of Prof. Jörg Hermann, who departed to the University of Bern, Switzerland and Prof. Richard Arculus, who retired. Neither has yet been replaced. Among post-doctoral fellows, Dr Marion Louvel went to a new post-doctoral position in Bristol, Dr Philipp Brandl returned to Germany, while Dr Charles LeLosq arrived from the Geophysical Laboratory of the Carnegie Institute of Washington. A former student from the group, Dr Guilherme Mallmann, will make a welcome return in 2016 to take up an ARC DECRA Fellowship. The group also benefits from hosting a number of distinguished Visiting Fellows engaged in collaborative research projects with academic staff and students.

Funding for a new electron microprobe totaling $1.6 M was secured through ARC LEIF (in 2014) and ANU Major Equipment funding schemes by a team led by Dr Greg Yaxley. After careful investigation into required specifications, a tender will go out in 2016. Two new computer-controlled piston-cylinder apparatus configured to a new RSES design were commissioned, and two more are in preparation. The computer control marks a useful advance in high-pressure experimentation for its improvement in the accuracy with which pressure can be measured. Several other laboratories in Australia and internationally have expressed interest in their design. Further funding for laboratory equipment was secured through an ARC LIEF grant to Dr John Mavrogenes and Prof. Hugh O’Neill, which will be used to rebuild Dr Mavrogenes’ hydrothermal laboratory and to commission a new ultra-high-pressure piston cylinder. The group failed to win any new ARC Discovery grants in the 2015 round, which will have an adverse impact on its operations and future directions.

Research continues into the experimental study of trace-element partitioning, and characterization of Fe and several trace-element valence states by XANES spectroscopy at the Australian Synchrotron. Use of this national facility has become an important part of the group’s research, so it was reassuring to learn in 2015 that funding support for the AS will continue forward on a secure basis.

Among the diverse activities undertaken by the surviving members of the group and their students, Greg Yaxley continued high-pressure experimental investigations of the fate of carbon in deeply subducted, altered mafic oceanic crust. Experiments by PhD student Melanie Sieber have investigated the carbonation of the cold serpentinite wedge above the fore-arc region of subduction zones by hydrous, CO2-bearing fluids liberated from the slab. Fixing of carbon as magnesite in a talc-bearing assemblage may result in development of a formerly unrecognised carbonate reservoir in the mantle, which could significantly influence carbon fluxes into the deeper mantle. Multi-anvil experiments are examining partial melting of carbonate eclogite subducted to lowermost upper mantle and mantle transition zone depths, and interactions of the resulting carbonate melts with reduced peridotite to form diamonds and hybrid silicate lithologies such as pyroxenites.

Figure 1: Back-scattered electron image off multi anvil experiment (13GPa, 1200°C) on a basalt + calcite composition, showing stishovite (dark grey) + garnet (mid-grey) + clinopyroxene (light grey) + carbonate melt (homogenous grey area at bottom of image) with rhenium (IV) oxide buffer (white).

Andrew Berry continued to use synchrotron radiation to investigate the speciation of redox variable elements and undertook experiments at the Advanced Photon Source in Chicago (the oxidation state of Fe in peridotitic garnet), European Synchrotron Radiation Facility in Grenoble (the oxidation state of Fe in eclogitic garnet) and Diamond Light Source in Oxfordshire (characterisation of a new material for the removal of As from drinking water).  He also spent a month as a Professor-Researcher at the Institut de Physique du Globe de Paris working with Daniel Neuville on the properties of silicate melts.

Hugh O’Neill has developed a method to parameterize Rare Earth Element pattern shapes with applications to basaltic magmatism and experimentally is working on the solubilities of Platinum Group Elements in silicate melts. His student, Paolo Sossi, who graduated in 2015, has measured isotopic fractionation of Fe among the major minerals of the mantle and has investigated the effect of cooling rates on the extent of disequilibrium in the compositions of olivines crystallizing from komatiitic liquids. His students and co-workers continue to measure diffusion of trace elements in olivine (Mike Jollands and Irina Zhukova), trace-element partitioning between plagioclase, clinopyroxene and silicate melts (Louise Schoneveld), the effect of pressure on trace-element partitioning through changes in structure and coordination in silicate melts (Eleanor Mare) and to study the complexities of how H2O substitutes into olivine (Pete Tollan and Rachel Stott) in order to understand better the deep Earth geochemical cycle of H2O. A new project to determine the phase relations of sulfide under mantle conditions as a function of pressure, temperature and oxygen fugacity (Johanna Sommer) has started.

John Mavrogenes has been investigating the generation of porphyry copper deposits by gas-brine reaction in volcanic arc, and, with Marion Louvel, has applied X-ray absorption spectroscopy using synchrotron radiation to study the hydrothermal controls on the genesis of REE deposits.

Visiting Fellow Dick Henley is working with Penny King in a new field of geochemistry: systematics of heterogenous gas reactions (chemisorption) at high temperatures, with applications in the fields of planetary and meteorite chemistry, volcanic processes and the origin of major metal accumulations such as porphyry copper deposits.

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