Compositional variation of tourmaline at high- and ultrahigh pressure

Tourmaline has been widely used as a petrogenetical indicator. There is, however, no general agreement if and how the compositional variability of tourmaline could be potentially used as a geobarometer. We want to test the hypothesis of enhanced potassium incorporation as well as increased incorporation of tetrahedral B into the tourmaline structure by a series of tourmaline-fluid (Ca,Na,K)-exchange experiments at ultrahigh pressure. If so, significant tetrahedral B must have a significant effect on the B isotope fractionation between fluid and tourmaline, which will be calibrated. The experimental part of the project will be accompanied by crystal-chemical and B isotopic analyses of tourmaline from high- and ultrahigh pressure rocks using well-known, previously characterized samples. We expect a better understanding of the large-scale, long-term B cycle during subduction processes.

Fig.: SEM-picture of synthetic K-rich tourmaline (with talc)

Contact

Dr. Bernd Wunder

Prof. Dr. Wilhelm Heinrich

Prof. Dr. Gerhard Franz, Technische Universität Berlin

Dr. Eleanor Berryman

Dr. Martin Kutzschbach