August 1, 1999-July 31, 2001
Level of Access
The primary goal of this research is to evaluate the chemical equilibria involving ferrous and ferric iron and hydrogen in metapelitic rocks from western Maine and related rocks at Black Mountain, New Hampshire. We will study samples from graphite, magnetite, and hematite-bearing rocks at three different metamorphic grades: garnet, lower sillimanite, and staurolite zone. This will permit the determination of:
(1) in situ partition coefficients for Fe3+ and Fe2+ among all the Fe-bearing phases and for H among hydrous phases;
(2) the temperature and fO2 dependence of Fe3+/Fetotal and effects of Fe3+ substitution on other cation substitutions plus their implications for geothermometry; and
(3) the cation substitutions that charge balance variations of H and Fe3+. We will also characterize and seek to understand Fe3+/Fetotal zoning within individual mineral grains as well as variation of Fe3+/Fetotal among grains of the same mineral in the same rock; ultimately, we will assess the effects of assemblage on Fe3+/Fetotal in the constituent mineral phases present.
These measurements will be made on standard 1" round petrographic thin sections using beam sizes of less than 10 x 15 micrometers and the relatively rapid, non-destructive techniques of synchrotron microXANES spectroscopy (SmX) for Fe3+/Fetotal, ion microprobe (SIMS) for H, and the electron microprobe (EPMA) for other major elements. With our analytical results in hand, we can begin to address the competing effects of assemblage and crystal chemistry on the incorporation of Fe2+ and Fe3+ in metapelite minerals. We also hope to effectively and quickly demonstrate the potential importance of SmX as a petrologic tool.
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Guidotti, Charles V., "Collaborative Research: Chemical Equilibria Involving Iron and Hydrogen in Metapelites From Western Maine" (2001). University of Maine Office of Research and Sponsored Programs: Grant Reports. 261.