EAR-PF: A new oxybarometer to quantify spatial and temporal scales of redox variation in subducting slabs

Megan Holycross博士被授予NSF博士后奖学金，以研究俯冲板块如何记录地球的深层氧循环。她的研究和公共服务将在史密森学会和耶鲁大学进行。固体地球中氧气的可用性影响行星的结构，岩石和矿石的化学性质以及大气的组成。地球氧化表面和还原内部之间的氧气质量转移发生在俯冲带，但俯冲板片本身的氧化状态及其对俯冲带岩石学、地球化学和地球动力学过程的影响仍然知之甚少。霍利克罗斯博士将进行实验，以校准榴辉岩中氧气的新替代物，榴辉岩是在俯冲板块上形成的变质岩，这些板块已经回到了地表。在实验校准之后，她将应用新的代理来确定古代和现代的天然榴辉岩套件如何跟踪俯冲带氧化态的空间和时间变化。在担任NSF博士后研究员期间，Holycross博士将在国家自然历史博物馆和耶鲁皮博迪自然历史博物馆举办教育活动，与公众分享地球科学的兴奋。她还将建立一个虚拟的点对点指导和支持小组，以连接美国8个以上机构的早期职业科学家。榴辉岩是大洋玄武岩在高压、高温作用下在俯冲板片上形成的。因此，它们可能保留了关于其玄武岩前体的氧化态（或氧逸度，fO2）的重要信息，或者，它们的氧化态可能是整个俯冲系统中氧化物质质量转移的结果。综合询问的榴辉岩fO2记录，并了解这些值的地质意义，需要一个实验校准的代理，可以应用到天然样品，使用常用的分析工具。榴辉岩矿物组合（在这里，金红石，石榴石和辉石）是一个新的fO2代理，将利用多价微量元素钒（V）的敏感性，在氧化还原环境的变化的发展的优秀候选人。钒的变化形态（V2+，V3+，V4+，V5+）超过地球相关的fO2，因此钒在不同阶段的结合应改变作为氧逸度的函数。榴辉岩熔融活塞缸实验将运行，以校准之间的金红石，辉石，石榴石和硅酸盐熔体作为fO2，压力和温度的函数的分配钒。新的fO2代用指标将应用于来自西非的太古代榴辉岩捕虏体和希腊基克拉泽斯俯冲复合体中的一个挖出的始新世岩石，以探测俯冲板片随时间的氧化还原变化（数十亿年的尺度）和空间（俯冲带的规模）该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

Dr. Megan Holycross has been awarded an NSF EAR Postdoctoral Fellowship to investigate how subducting slabs record the Earth's deep oxygen cycle. Her research and public service will take place at the Smithsonian Institution and at Yale University. The availability of oxygen in the solid Earth influences the structure of the planet, the chemistry of rocks and ores as well as the composition of the atmosphere. Mass transfer of oxygen between the Earth's oxidized surface and its reduced interior takes place at subduction zones, but the oxidation state of the subducting slab itself, and its consequences for petrological, geochemical and geodynamic processes in subduction zones, is still poorly understood. Dr. Holycross will perform experiments to calibrate a new proxy for oxygen in eclogites, metamorphic rocks formed on subducting slabs that have made their way back to the surface. Following experimental calibration, she will apply the new proxy to determine how ancient and modern suites of natural eclogites track spatial and temporal variations in the oxidation state of subduction zones. During her tenure as an NSF Postdoctoral Fellow, Dr. Holycross will host educational events at both the National Museum of Natural History and the Yale Peabody Museum of Natural History to share the excitement of geoscience with the public. She will also develop a virtual peer-to-peer mentoring and support group to connect early career scientists at 8+ U.S. institutions. Eclogites form on subducting slabs during high-pressure and high-temperature alteration of oceanic basalts. Therefore they may retain important information about the oxidation state (or oxygen fugacity, fO2) of their basalt precursor, or alternately, their oxidation state may be a result of the mass transfer of oxidized materials throughout the subduction system. Comprehensive interrogation of the eclogite fO2 record, and understanding the geological significance of these values, requires an experimentally calibrated proxy that can be applied to natural samples using commonly available analytical tools. Eclogitic mineral assemblages (here, rutile, garnet and pyroxene) are excellent candidates for the development of a new fO2 proxy that will utilize the sensitivity of the multivalent trace element vanadium (V) to changes in redox environment. Vanadium shifts speciation (V2+, V3+, V4+, V5+) over Earth-relevant fO2s, and thus the incorporation of Vanadium in different phases should change as function of oxygen fugacity. Eclogite-melting piston-cylinder experiments will be run to calibrate the partitioning of Vanadium between rutile, pyroxene, garnet and silicate melt as a function of fO2, pressure and temperature. The new fO2 proxy will be applied to Archean eclogite xenoliths from West Africa and an exhumed Eocene terrane from the Cyclades subduction complex in Greece to probe redox changes in subducting slabs over time (scale of billions of years) and space (scale of a subduction zone).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.