August F. Koster van Groos
My research interests are diverse, although the main thrust of my work is in experimental studies at elevated temperatures and pressures that are aimed to improve the understanding of processes occurring in the upper mantle and crust. Igneous rocks, such as carbonatites and kimberlites, indicate the presence of carbon dioxide in the upper mantle, and suggest that the mantle was and is an important and active carbonate reservoir. Thus, for the understanding of long-term changes in the geochemical cycle of CO2, this mantle reservoir is of primary importance. Non-equilibrium partition of trace elements between the granitic melts and an exsolving vapor needs to be understood in more detail. Important in this process is the diffusion rate of various simple and complex components in siliceous melts. Applications relate to the differentiation of andesitic and granitic melts, formation of ore deposits, etc. Temperature strongly affects the weathering rate of silicate minerals. These effects are an important factor in geochemical considerations. We have demonstrated that the dissolution rate of olivine is considerably more temperature dependent than previously thought. Geological implications extend to the nature and total mass of the continental crust throughout the history of the earth. I developed a high-pressure (to 950 °C and 10 kbar) differential thermal analysis system (HP-DTA) for studies in both open and closed systems. This allowed me to work, together with Steve Guggenheim , on the stability of water and other substances such as organic material at the interlayer in selected clay minerals. Finally, I have worked on stable chlorine isotopes and their application to a range of geological environments. .
Selected recent publications:
Awad, A., Koster van Groos A.F. and Guggenheim S., 2000. Forsteritic olivine: Effect of crystallographic direction on dissolution kinetics. Geochimica et Cosmochimica Acta, 64: 1765-1772.
Bai, T.B. and Koster van Groos, A.F. , 1999. The distribution of Na, K, Rb, Sr, Al, Ge, Cu, W, Mo, La, and Ce between granitic melts and coexisting aqueous fluids. Geochimica et Cosmochimica Acta, 63: 1117-1131.
Bai, T.B. and Koster van Groos, A.F. , 1998. Phase relations in the system MgO-NaCl-H2O: The dehydroxylation of brucite in the presence of NaCl-H2O fluids. American Mineralogist, 83: 205-212.
Eggenkamp, H.G.M. and Koster van Groos, A.F. , 1997. Chlorine stable isotopes in carbonatites: evidence of isotopic disequilibrium in the mantle. Chemical Geology, 140: 137-140.
Wang, S., Koster van Groos, A.F. and Guggenheim, S., 1996. The effect of CaCl2-H2O fluids on the dehydration of Ca-exchanged montmorillonite (SWy-1) at elevated temperatures and pressures. Geochimica et Cosmochimica Acta, 60: 2167-2172.