Application of the electron microprobe to quantitative analysis of ferric-ferrous ratio in silicate glasses, new experimental calibration

• Applicant: Dr. Renat Almeev, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257090887

The ferric/ferrous ratio in natural silicate melts is widely used for estimations of the redox conditions, which together with other thermodynamic variables such as temperature, pressure and water activity control the physical and chemical properties of the magmatic melts. Despite the progress in developments of analytical techniques, there is still crucial need of the method for direct determinations of ferric-ferrous ratio in heterogeneous natural objects such as melt inclusions or naturally quenched glasses as well as in the experimental products of partial crystallization or melting. At local scale, Fe3+/Fe2+ measurements in experimental and natural samples can be performed by a number of methods. Amongst this sophisticated techniques, the use of the electron microprobe for ferric-ferrous ratio determinations would be the ideal due to its low costs. The measurement of ferric-ferrous ratio using electron microprobe is based on the property of transition metals to exhibit a shift of the L-alpha and L-beta peaks and L-alpha and L-beta intensity ratios in X-ray emission spectra with a change in the oxidation states. Several methods (peak shift and flanks methods) has been developed and verified for the iron-bearing silicate minerals. Only one calibration of the peak shift method (Fialin et al., 2011) exists in the literature in application to silicate glasses. However application of this calibration to strongly oxidized and reduced glasses demonstrate significant deviation of the predictive model. This project is focused on a next development of the model of Fialin et al. (2001) and is based on new calibration of the location of the Fe-L-alpha peak as a function of Fe content, using a new set of silicate glasses. This dataset includes significantly larger range of glass compositions, which was produced in a wide range of redox conditions. In contrast to the previous approach where two sets of minerals with ferric and ferrous iron were used to calibrate pure Fe2+-bearing and pure Fe3+-bearing curves, experimental glasses produced at reduced and oxidized conditions will be utilized.

• DFG Programme: Research Grants
• International Connection: Russia
• Participating Persons: Dr. Alexander Borisov, Ph.D.; Professor Dr. Jürgen Koepke