Collaborative Research: Chemical Equilibria Involving Iron and Hydrogen in Metapelites From Western Maine

本研究的主要目的是评估缅因州西部的变质岩石和新罕布什尔州黑山的相关岩石中亚铁和三价铁与氢的化学平衡。 我们将研究三种不同变质等级的石墨、磁铁矿和含赤铁矿岩石的样品：石榴石、下硅线石和十字石带。 这将有助于确定：（1）Fe ~（3+）和Fe ~（2+）在所有含Fe相中的原位分配系数和H在含水相中的原位分配系数;（2）Fe ~（3+）/Fe ~（3+）的温度和fO ~ 2依赖性以及Fe ~（3+）取代对其它阳离子取代的影响及其地质测温学意义;（3）平衡H和Fe ~（3+）电荷变化的阳离子取代。 我们还将描述和试图了解单个矿物颗粒内的Fe 3 +/Fe total分带以及同一岩石中相同矿物颗粒之间Fe 3 +/Fe total的变化;最终，我们将评估组合对构成矿物相的Fe 3 +/Fe total的影响。这些测量将在标准的1”圆形岩石薄片上进行，使用小于10 x 15微米的光束尺寸和相对快速的非破坏性技术，即同步加速器微XANES光谱（SmX）用于Fe 3 +/Fe总，离子微探针（西姆斯）用于H，电子微探针（EPMA）用于其他主要元素。有了我们的分析结果，我们就可以开始讨论集合和晶体化学对Fe 2+和Fe 3+在变岩矿物中结合的竞争作用。 我们也希望有效和快速地证明SmX作为岩石学工具的潜在重要性。

9902857GuidottiThe primary goal of this research is to evaluate the chemical equilibriainvolving ferrous and ferric iron and hydrogen in metapelitic rocks fromwestern Maine and related rocks at Black Mountain, New Hampshire. We willstudy samples from graphite, magnetite, and hematite-bearing rocks at threedifferent metamorphic grades: garnet, lower sillimanite, and staurolitezone. This will permit the determination of: (1) in situ partitioncoefficients for Fe3+ and Fe2+ among all the Fe-bearing phases and for Hamong hydrous phases; (2) the temperature and fO2 dependence ofFe3+/Fetotal and effects of Fe3+ substitution on other cation substitutionsplus their implications for geothermometry; and (3) the cationsubstitutions that charge balance variations of H and Fe3+. We will alsocharacterize and seek to understand Fe3+/Fetotal zoning within individualmineral grains as well as variation of Fe3+/Fetotal among grains of thesame mineral in the same rock; ultimately, we will assess the effects ofassemblage on Fe3+/Fetotal in the constituent mineral phases present. These measurements will be made on standard 1" round petrographic thinsections using beam sizes of less than 10 x 15 micrometers and therelatively rapid, non-destructive techniques of synchrotron microXANESspectroscopy (SmX) for Fe3+/Fetotal, ion microprobe (SIMS) for H, and theelectron microprobe (EPMA) for other major elements. With our analyticalresults in hand, we can begin to address the competing effects ofassemblage and crystal chemistry on the incorporation of Fe2+ and Fe3+ inmetapelite minerals. We also hope to effectively and quickly demonstratethe potential importance of SmX as a petrologic tool.