Geophysics, Geodynamics and Tectonics
Origin and evolution of primary melts.
We currently have very little direct evidence of the composition of our mantle. Kimberlites are the deepest magmas known to erupt on the Earth's surface, and thus provide us with discrete, direct sampling of the upper mantle. Kimberlites are mostly found as carrot shaped pipes which are thought to reach the surface of the Earth directly from the source region (150 - 200 km). In spite of this, they do not correctly represent the source region due to the alteration experienced upon ascent and after emplacement (eg. serpentinisation). I am investigating several questions which currently dominate kimberlite research:
1. Primary melt composition and in particular the volatile content of these magmas.
2. Temperature of the magma at the source region.
3. The carbonatitic and kimberlitic co-genetic link. Are they related, and if so, to what extent?
4. How (and by how much) are kimberlites altered during ascent, emplacement and post-emplacement.
In addition to extending our understanding of how kimberlitic magmas form, constraining the volatile content, source and emplacement temperatures will allow us to calculate the primary melt composition more precisely and further develop ideas on eruption dynamics and thermodynamic models. Two main approaches are:
- Experimental: Using simplified rock (mantle) compositions to study the melting phase relations by performing experiments at varying pressure and temperatures. For example, taking the simple model CaO-MgO-Al2O3-SiO2-CO2 (CMAS-CO2) and adding H2O and K2O to see how these two components affect the solidus and melting relations. The water and K-absent system (CMAS-CO2) gradually generates a kimberlitic liquid from a carbonatitic liquid with increasing temperature and pressure. Our experiments demonstrate that the onset of melting occurs at far lower temperatures with the addition of water and K. Furthermore, liquid immiscibility occurs at temperatures exceeding 1250oC, thus illustrating a different method of producing kimberlitic and carbonatitic liquids.
- Petrology and geochemistry: Studying the rocks of an exceptionally young (Holocene) kimberlite volcano, Igwisi Hills Volcano, Tanzania. As olivine is the first phase to crystallize from the melt, most of the current research on these samples is concentrated on the olivine chemistry (including the water content) of Igwisi olivine.