Experimental Petrology Introduction

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 apparatuses 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, several of which are equipped for precise control of oxygen and sulfur fugacities by gas mixing; eleven solid-media piston-cylinder devices for generating pressures to 6 GPa and temperatures in excess of 2000°C, a multi-anvil apparatus, which can presently achieve pressures of 27 GPa; and a well-equipped hydrothermal laboratory.

These high-temperature, high-pressure apparatuses are complimented by an array of microbeam analytical techniques, including a Cameca SX100 electron microprobe; laser-ablation ICP-MS, which is now being used regularly to analyse trace-elements in experimental run products; a STOE STADIP powder X-ray diffractometer; and FTIR spectroscopy for the determination of H₂O, CO₂ and other volatile species in minerals and glasses. To complement this latter facility, the group acquired a Agilent 6850 Gas Chromatograph, which has been combined with a capsule-piercing device to enable the extraction and analysis of small quantities of C-O-H fluids from high-pressure experimental run products.

As well as the conventional 1/2 inch and 5/8 inch apparatus for use to 4 GPa, the group's piston-cylinder laboratory also runs a high-pressure device that is now operating regularly at 6.5 GPa; the laboratory also has two large-capacity piston-cylinder devices that take 30 mm and 50 to 65 mm diameter pressure assemblies respectively, enabling pressure to be controlled extremely accurately, and which are capable of synthesising relatively large volumes of high pressure phases for detailed mineralogical studies. A novel diamond composite hard material, developed in these apparatuses and now under commercial production, offers promise as an anvil material to extend the pressure range of the multi-anvil apparatus above 26 GPa, thereby allowing detailed experimental exploration of the pressure-temperature regime of the Earth's lower mantle. To further this research the multi-anvil apparatus has now been refurbished and provided with full computer control of pressure and temperature.

In recent years the group has become increasingly involved in developing methods to characterise geologic materials by X-ray absorption spectroscopy (XANES) and related techniques that use synchrotron radiation. Research in this area is presently concentrating on oxidation states in silicate melts, including in-situ measurements at temperatures to 1500°C, and speciation in ore-forming hydrothermal solutions. Members of the group continue to investigate conditions and processes in the Earth's upper mantle (Professors David Green and Hugh O'Neill, Dr Robert Rapp), and metamorphism in the continental crust (Dr Joerg Hermann), as well as the physical chemistry of ore-forming solutions (Drs John Mavrogenes, Katy Evans).