EAR-PF Determining links between magma redox heterogeneity in ocean island basalts and near-surface processes of the ancient and present day

玛丽·E.彼得森已被授予美国国家科学基金会博士后奖学金，在加州理工学院开展研究和教育活动。不同构造背景下形成的岩浆具有很大的地球化学变异性，在某些情况下反映了古代再循环物质与亏损上地幔混合的痕迹。这项调查将确定洋岛玄武岩的地幔源的氧化状态是否与洋中脊或弧地幔源有明显的不同。了解岩浆的氧化状态是很重要的，因为它将使科学家能够辨别地幔熔融开始的深度以及什么矿物可能从岩浆中生长出来。该项目的分析范围包括从三个洋岛（加拉帕戈斯群岛、冰岛和巴芬岛）的熔岩中分离出一套特征良好的玻璃和熔融包裹体，以测量可用于推断地幔氧化状态的地球化学参数（例如，三价铁与总铁的比率、氧同位素、挥发性和微量元素浓度）。此外，彼得森博士将开发和领导一个研究生水平的研讨会，开放给学生在地质科学，材料科学和化学探索地球材料的氧化态的地球化学影响。本次调查的数据将收集使用微X射线吸收近边结构光谱（XANES），以测量Fe 3 +/总Fe的比例。这些测量将结合原位二次电离质谱（西姆斯）测量的氧同位素，挥发性和微量元素，以确定是否在玻璃的Fe 3 +/总Fe比的变化是由于浅层次的过程或地幔源的氧化态的变化。这些测量将建立在加拉帕戈斯的初步数据基础上，同时扩大到包括冰岛和巴芬岛。本研究的结果将继续增长现有的数据库同步加速器测量的Fe形态在天然硅酸盐玻璃，以发展岩浆氧化还原和板块构造循环之间的联系的基本认识。通过限制地幔端元的氧化还原性质，我们可以建立一个固体地球氧化还原演化的模型，并为过去将固体地球和地表氧化还原条件联系起来的现有模型或假设提供信息。

Dr. Mary E. Peterson has been granted an NSF EAR Postdoctoral fellowship to carry out research and education activities at the California Institute of Technology. Magma generated in different tectonic settings has great geochemical variability, in some cases reflecting traces of ancient recycled material mixing with depleted upper mantle. This investigation will determine if the oxidation state of the mantle source for ocean island basalts is measurably different than either mid-ocean ridge or arc mantle sources. Understanding the oxidation state of the magma is important because it will allow scientists to discern the depth where mantle melting was initiated and what minerals may grow from the magma. The analytical scope for the project involves isolating a suite of well characterized glass and melt inclusions from lavas from three ocean island settings (the Galapagos Archipelago, Iceland and Baffin Island) to measure geochemical parameters that can be used to infer oxidation state of the mantle (for example, the ratio of ferric to total iron, oxygen isotopes, volatile and trace element concentrations). In addition, Dr. Peterson will develop and lead a graduate level seminar, open to students in geological science, materials science and chemistry to explore the geochemical implications of the oxidation state of Earth materials. The data for this investigation will be collected using micro x-ray absorption near-edge structure spectroscopy (XANES) to measure Fe3+/total Fe ratios. These measurements will be combined with in situ secondary ionization mass spectrometry (SIMS) measurements of oxygen isotopes, volatile and trace elements, to determine if variations in Fe3+/total Fe ratios of the glass are due to shallow level processes or variability in the oxidation state of the mantle source. These measurements will build on preliminary data from the Galapagos while expanding to include the Iceland and Baffin Island. The results of this study will continue to grow the existing database of synchrotron measurements of Fe speciation in natural silicate glass in order to develop a basic understanding of the links between magma redox and plate tectonic cycling. By constraining the redox properties of mantle end-members, we can build a model for the evolution of solid Earth redox and inform existing models or hypotheses that link solid Earth and surface redox conditions in the past.