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

Mary E. Peterson博士获得美国国家科学基金会EAR博士后奖学金，在加州理工学院开展研究和教育活动。在不同构造环境下产生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枯竭的上地幔混合的痕迹。这项研究将确定洋岛玄武岩地幔源的氧化状态是否与洋中脊或弧型地幔源有明显的不同。了解岩浆的氧化状态很重要，因为它将使科学家能够辨别地幔融化开始的深度，以及岩浆中可能生长出哪些矿物质。该项目的分析范围包括从三个海洋岛屿（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，铁与总铁的比率、氧同位素、挥发性和微量元素浓度）。此外，Peterson博士将开发并领导一个研究生水平的研讨会，向地质科学，材料科学和化学的学生开放，探索地球材料氧化态的地球化学含义。本研究的数据将使用微x射线吸收近边结构光谱（XANES）来测量Fe3+/总铁比。这些测量将与氧同位素、挥发性和微量元素的原位二次电离质谱（SIMS）测量相结合，以确定玻璃中Fe3+/总Fe比率的变化是由于浅层过程还是地幔源氧化状态的变化。这些测量将建立在加拉帕戈斯群岛的初步数据基础上，同时扩大到包括冰岛和巴芬岛。这项研究的结果将继续扩大现有的同步辐射测量天然硅酸盐玻璃中铁形态的数据库，以便对岩浆氧化还原和板块构造循环之间的联系有一个基本的了解。通过约束地幔端元的氧化还原性质，我们可以建立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.