Experimental Petrology and Petrochemistry Group

Backscatter electron image of exotic Pd tellurides and sulphide melt in contact with mss and telluride melt. (Helmy et al., CMP, 2007)

What is Experimental Petrology?

Unlike surface processes such as weathering and erosion that can be observed in a human time-scale, processes that lead to the formation of igneous rocks, such as granites and basalts, tend to occur deep in the Earth and thus cannot be directly observed. However, under controlled laboratory conditions it is possible to simulate conditions relevant to processes that occur in Earth's interior (i.e. higher pressures and temperatures). This experimental work comprises a branch of Earth Sciences dubbed Experimental Petrology.

Experimental Petrology involves simulating igneous or metamorphic conditions with specialized machines using a range of materials that mimic compositions akin to the interior of the Earth. Samples may include synthetic minerals or mixes of minerals, fluids such as H₂O and/or CO₂ or actual rock compositions. We can simulate open systems (open to matter and heat exchange), and closed systems (only open to heat exchange). Moreover, we can investigate the effects that variables such as temperature, pressure, oxidation state (or oxygen fugacity) etc. may have on a variety of rock forming processes.

In short, Experimental Petrology is extremely important as a window to processes which occur deep in the Earth’s mantle, and lead to formation of the rocks and minerals that we have access today on the surface of the Earth.

Current aims of the group

Here at the Experimental Petrology and Petrochemistry group, we mostly deal with the high-temperature partitioning of metals (siderophile and chalcophile elements), as a function of intensive variables such as oxygen and sulphur fugacity, T and P. We also aim to look at the role of sulphur and sulphides in the partitioning of such elements in order to attempt to understand the abundances of these elements in the Earth’s mantle, as well as processes that lead to the fractionation and enrichment of these elements in a variety of rock suites.

Another subject of active research is the oxidation state of the mantle and parameters that control it. The oxidation state is a fundamental parameter for a wide variety of mantle processes, such as the temperature of first melting, the composition of partial melts, the convection behaviour (rheological properties) of the mantle, the stability and composition of fluid C-H-O-S phases in the mantle, and atmospheric evolution during the Archean when the early atmosphere was controlled by outgassing. The sample material available from Earth's mantle is extremely limited and far from being representative for the whole mantle. Therefore variations in oxidation state with time or with depth, or as a function of plate-tectonic position of the mantle, are classic parameters that can only be modelled experimentally.