I am interested in the origin and evolution (i.e. petrogenesis) of carbonatites, kimberlites and other alkaline rocks derived from the Earth's mantle. My research focuses on the mineralogy of these rocks in an attempt to understand how it ties in with the behavior of specific elements or element groups and specific evolutionary processes in magmas and fluids. Ultimately, the goal of this research is to develop an integrated petrogenetic model for individual igneous complexes or igneous provinces, a model that would account for the relative timing, tectonic setting, geochemistry, petrographic and mineralogical makeup, and economic potential of specific groups of rocks. Alkaline and related rocks derived from the Earth's mantle are an important source of many mineral resources, including niobium ore, rare earths and diamonds. In addition, the complex and variable mineralogy and chemistry of these rocks make them an extremely challenging research material. Their mineralogical and textural diversity is reflected in the fact that about one-third (!) of all igneous rock names ever proposed refer to alkaline or carbonatitic rocks.
One way of backtracking the evolution of such complex igneous rocks as carbonatites or kimberlites is by studying their constituent minerals. Any, however minor, changes in crystallization conditions or magma/fluid chemistry are recorded in the composition and crystal structure of minerals, as well as in their interrelations. For example, these images of perovskite crystals from different alkaline rocks
document multiple changes in magma chemistry during perovskite crystallization, transitions from growth to resorption and back to growth again, and variations in morphology and surface properties of perovskite crystals. Needless to say, the petrogenetic record is easier to decipher and interpret if (i) there are many different minerals present in the rock in the first place, and (ii) there are many minerals of variable chemistry (i.e. capable of adjusting to changing crystallization conditions). Alkaline and related rocks readily meet both these "requirements". Intrusive kimberlites, for example, may contain over a dozen different minerals, most of which do not have a fixed formula and exhibit a remarkable variation in chemistry: (K,Ba,Na)(Mg,Fe2+,Fe3+,Ti,Al,Mn)3(Al,Fe3+,Si)2Si2O10(OH,F)2 (micas), (Mg,Fe2+,Fe3+,Mn)(Cr,Al,Ti,Mg,Fe2+,Fe3+)2O4 (spinels), (Ca,REE,Na,Sr)(Ti,Fe,Nb)O3 (perovskite), etc. Variations in trace-element abundances (e.g., Co, Y and Zr) add to this complexity and provide further insight into the conditions at which these minerals crystallize. Experimental studies and thermodynamic calculations help us constrain these conditions and come up with a quantitative estimate for temperature, pressure and other parameters that control the emplacement and crystallization of mantle-derived melts.
My recent research has focused on the applicability of several different minerals and mineral groups, found in a wide spectrum of alkaline rocks (like garnets, apatites, perovskites and pyrochlores), as petrogenetic sensors. My collaborators and I are investigating the crystal chemistry of these minerals and their adaptability to chemical and physical changes in their crystallization environment. These data provide a framework for the interpretation of genetic and temporal relationships among different mineral parageneses, rock units, magma types and, if all goes well, discrete igneous complexes.
Within the scope of this research, there are opportunities for honors, MSc and PhD projects in mineralogy/petrology of carbonatites, kimberlites and alkaline rocks from North America and around the world, as well as projects focused on specific minerals and their role in the evolution of alkaline magmas.
