Nuclear Reaction Analysis of Biotite Minerals
EMSL Project ID
13790
Abstract
Understanding the chemical processes, crystal chemistry, and elemental composition evolution in minerals is highly important in geochemical, environmental, and geophysical sciences. Biotite, K(Fe2+,Mg,Fe3+,Ti)3[(Si,Al)4O10](OH,F,Cl)2, is a hydrated ferromagnesian silicate that is common in most mafic, intermediate, and felsic igneous rocks. It forms over a wide range of crystallization conditions and reacts very sensitively to changes in the physical and chemical conditions such as oxygen and halogen fugacities, temperature, pressure, and chemical composition of the host magmas. Thus, reactions involving biotite are potentially useful in determining oxygen fugacity (fO2) of granitic rocks, a valuable indicator of redox conditions of magmas at their formation. Careful application of the reaction chemical equilibria requires a complete characterization of biotite in order to determine the activity of its annite component, including major element composition, Fe3+/Fe2+ratio, and hydroxyl content. In the proposed research, the major elements and associated concentrations in the biotite minerals (about 30 m thick, mounted on glass plates) have already been measured by Martin Reich using electron microprobe techniques (EMPA) at the University of Michigan. In addition, the Fe3+/Fe2+ ratio of 12 samples has also been determined by Martin Reich in conjunction with Prof. Darby Dyar at Mount Holyoke College, using Mössbauer spectroscopy. The hydroxyl contents will be determined by nuclear reaction analysis (NRA) in the ion beam analysis laboratory at the Environmental Molecular Sciences Laboratory (EMSL), Pacific North-West National Laboratory (PNNL). The hydrogen and water content determination of these samples is quite important from basic science and environmental technology perspective and, therefore, needs special attention. Using energetic ion beam techniques involving bombarding the sample with MeV ionizing radiation and detecting the ejected particles is the only available and well suited technique to determine the lighter elements. The qualitative and quantitative information obtained using ion beam techniques will be highly useful to understand the chemical reactions and will indirectly address properties of molecular bonding on the surface and in the bulk of the mineral. Results of this investigation using the facilities at PNNL will thus have implications in understanding the physical and chemical processes at the molecular level. The research will also involve thermodynamic calculations, which involve models at 650, 700, 750 and 800°C, with oxygen fugacities derived at each temperature. The results of this research will be compared with oxygen fugacity and geothermometry based on data from two oxides in the same rocks.
Project Details
Project type
Exploratory Research
Start Date
2005-03-01
End Date
2007-03-22
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Ramana CV, U Becker, V Shutthanandan, and CM Julien. 2008. "Oxidation and Metal-Insertion in Molybdenite Surfaces: Evaluation of Charge-Transfer Mechanisms and Dynamics ." Geochemical Transactions 9(8):, doi:10.1186/1467-4866-9-8