POWRE: Synchrotron Micro-XANES Study of Fe Redox in Mantle Phases

[806182]本研究的目的是测量地幔捕虏体中含铁相中Fe3+和Fe2+以及含水相中H的原位分配系数，并进行地幔模拟实验。对实验运行的分析将提供氢通过氧化还原交换传输动力学的定量数据。在自然样品中，提出的研究将首次在原位，真正的微观尺度测量地幔矿物中的Fe3+ /EFe。使用从以前研究得很好的岩石中自然产生的样品，将允许在严格限制的岩石学框架内考虑结果，其中将考虑压力，温度和矿物组合的影响。这些测量将在标准的1英寸圆形岩石薄片上进行，使用光束尺寸小于10 x 20 um和相对快速的非破坏性技术，SmX用于Fe3+/EFe，离子微探针（SIMS）用于h，电子微探针（EPMA）用于其他主要元素。P.I.s将致力于了解Fe3+/EFe在单个矿物颗粒中的分带，同一岩石中同一矿物颗粒中Fe3+/EFe的变化，Fe3+/EFe对温度和压力的依赖（及其对地热和地球气压的影响），以及H+， Fe3+和Fe2+含量变化的电荷平衡机制。有了这些结果，P.I.s可以解决以下问题：1)化学分析如何与电子探针对Fe3+和H+的估计进行比较；2)这些差异如何影响共生矿物间Fe2+/Mg、Fe3+/ Al、Fe3+/ Cr3+等元素的分布；3)这些分布系数如何影响密集变量的岩石学解释？4)完整的分析是否影响阳离子位点分配（相对于仅通过EPMA获得的数据）？5)分布系数是否为解释矿物成分的密集参数提供了新的见解？6)完整的分析是否显示EPMA无法看到的化学分区？用Ca带化法推断氧化/脱氢过程；7) Fe3+和H+是如何相关的，这种关系对地幔fO2和fH2的估算有什么意义？一旦完成，所提出的研究计划将能够对无法获得详细表征的岩石进行Fe3+， H+等成分变量的估计表达式。资金将用于支持私家侦探兼职在每两个夏天，并支持她在第二学年，使她能够利用新的SmX工具的令人兴奋的发展优势。

9806182DyarThe goal of this research is to measure in situ partition coefficients for Fe3+ and Fe2+ among all the Fe-bearing phases and for H among hydrous phases in mantle xenoliths and mantle-analog experimental runs. The analyses of experimental runs will provide quantitative data on the kinetics of hydrogen transport via redox exchange. In the natural samples, the proposed research will generate the first ever in situ, truly microscale measurements of Fe3+ /EFe in mantle minerals. Use of naturally occurring samples from previously well-studied rocks will allow results to be considered within a tightly constrained petrologic framework in which the effects of pressure, temperature, and mineral assemblages will be considered. These measurements will be made on standard 1" round petrographic thin sections using beam sizes of less than 10 x 20 um and the relatively rapid, non-destructive techniques of SmX for Fe3+/EFe, ion microprobe (SIMS) for h, and the electron microprobe (EPMA) for other major elements. The P.I.s will devote their efforts to understanding zoning of Fe3+/EFe within individual mineral grains, variation of Fe3+/EFe among grains of the same mineral in the same rock, the temperature and pressure dependence of Fe3+/EFe (and implication for geothermometry and geobarometry), and substitution mechanisms that charge balance variations in H+, Fe3+, and Fe2+ contents. With these results, the P.I.s can address the questions of 1) How do chemical analyses compare to electron microprobe estimates of Fe3+ and H+?; 2) How do these differences affect distribution of Fe2+/Mg, Fe3+/ Al, Fe3+/ Cr3+ etc. between coexisting minerals?; 3) How do these distribution coefficients affect petrologic interpretation of intensive variables?; 4) Do complete analyses affect cation site assignments (relative to those obtained only by EPMA only)?; 5) Do the distribution coefficients offer new insights into ways to interpret intensive parameters from mineral compositions?; 6) Do complete analyses show chemical zonation that cannot be seen with EPMA? Ca zonation be used to infer oxidation/dehydrogenation history?; and 7) How are Fe3+ and H+ related, and what are the implications of this relationship for estimation of mantle fO2 and fH2 ? Once completed, the proposed program of study will enable formulation of expressions for estimating compositional variables as Fe3+, H+, etc. for rocks in which such detailed characterizations are not available. Funding will be used to support the P.I. part-time during each of two summers, and to support her during the second academic year so that she can take advantage of the exciting development of the new SmX tool.