Volcanoes exist because of the supply of magma (typically melt + crystals +/- fluid) from below. Magma, in turn, is generated by partial melting of either crustal or mantle rocks. Several aspects of the melting process are currently especially topical, and will be incorporated into this group’s project goals. VAMOS will focus on main aspects of magma generation and its movement through the crust, its emplacement at crustal levels or its ascent and eruption on the Earth’s surface.
Rocks undergo solid-state changes that affect their geochemical and mechanical properties; such changes are responsible for producing metamorphic terranes and represent a critical piece of the melt genesis problem. Melting rock is complicated: it is simultaneously a thermal, mechanical, and chemical process. Hence, to describe melting processes, a thermodynamic approach will be needed and this will ultimately be coupled to models of magma migration in the crust and volcanic conduits. We know the approximate mineral assemblages for different P-T regimes imposed on different lithologies. What is less known are the effects of minor and trace light elements (e.g., B, Cl, Br, F, S) on the thermodynamic stabilities of minerals and melts. Some of this group’s work will address how the presence of halogens in the source region affects melt productivity.
Once generated, melts tend to start moving (typically upwards). A complexity is that the chemical composition of melts strongly changes on their way upwards. Moreover, the physical behavior of magmas during eruption depends to a large extent on volatile components such as H2O, CO2 and SO2. The explosivity and thus the hazards presented by volcanoes depend on the dissolution and exsolution properties of various gas species in melts. Many shallow magma chambers underneath volcanoes appear to be regularly replenished by a deeper source. Yet, what this deeper source is and how it works physically remains puzzling.
Photograph of a palaeo-melt-transfer network in mid crustal rocks from Namibia. Such networks show the way in which melt and magma are drained from the source region and transported through the crust to higher levels.
Calculated phase diagram showing the high temperature stability of minerals and melt. such calculations allow us to constrain the melt production in a wide range of rocks as a function of pressure and temperature.
Prof. Richard White leads the group on phase equilibria modelling of crustal rocks.