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

EAR-PF：一种新的氧压计，用于量化俯冲板片中氧化还原变化的空间和时间尺度

• 批准号: 1855208
• 负责人: Megan Holycross
• 金额: $ 17.4万
• 依托单位: Holycross, Megan Elizabeth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-06-01 至 2023-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1855208&HistoricalAwards=false
• 关键词: EAR; PF; new; oxybarometer; quantify

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.

Megan Holycross 博士获得了 NSF EAR 博士后奖学金，以研究俯冲板片如何记录地球深部氧循环。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着地球的结构、岩石和矿石的化学成分以及大气的成分。地球氧化表面与其还原内部之间的氧质量传递发生在俯冲带，但俯冲板片本身的氧化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来校准榴辉岩中氧的新替代物，榴辉岩是在俯冲板块上形成的变质岩，这些板块已经返回地表。经过实验校准后，她将应用新的代理来确定古代和现代的天然榴辉岩组如何追踪俯冲带氧化态的空间和时间变化。在担任美国国家科学基金会博士后研究员期间，霍利克罗斯博士将在国家自然历史博物馆和耶鲁大学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精彩。她还将建立一个虚拟的同行指导和支持小组，以联系超过 8 个美国机构的早期职业科学家。榴辉岩是在海洋玄武岩高压和高温蚀变过程中在俯冲板片上形成的。因此，它们可能保留有关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氧化物质在整个俯冲系统中传质的结果。对榴辉岩 fO2 记录的全面询问，并了解这些值的地质意义，需要一个经过实验校准的代理，可以使用常用的分析工具应用于自然样品。榴辉岩矿物组合（此处为金红石、石榴石和辉石）是开发新型 fO2 代理的绝佳候选者，该代理将利用多价微量元素钒 (V) 对氧化还原环境变化的敏感性。钒会改变与地球相关的 fO2 的形态（V2+、V3+、V4+、V5+），因此不同相中钒的结合应随着氧逸度的函数而变化。将进行榴辉岩熔化活塞缸实验，以校准钒在金红石、辉石、石榴石和硅酸盐熔体之间的分配，作为 fO2、压力和温度的函数。新的 fO2 代理将应用于西非的太古宙榴辉岩捕虏体和希腊基克拉泽斯俯冲杂岩中挖出的始新世地体，以探测俯冲板片随时间（数十亿年规模）和空间（俯冲带规模）的氧化还原变化）。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Garnet crystallization does not drive oxidation at arcs

石榴石结晶不会导致电弧氧化

• DOI: 10.1126/science.ade3418
• 发表时间: 2023-05
• 期刊: Science
• 影响因子: 56.9
• 作者: Holycross, Megan;Cottrell, Elizabeth
• 通讯作者: Cottrell, Elizabeth

Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks

俯冲变沉积岩氧化板片衍生的脱挥发分流体

• DOI: 10.1038/s41561-022-00904-7
• 发表时间: 2022-03-17
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: J. Ague;S. Tassara;M. Holycross;Ji‐Lei Li;E. Cottrell;E. Schwarzenbach;C. Fassoulas;T. John
• 通讯作者: T. John

Fe Kα XANES, Fe Kβ HERFD XANES and EPMA flank method determinations of the oxidation state of Fe in garnet

Fe Kα XANES、Fe Kβ HERFD XANES 和 EPMA 侧翼法测定石榴石中 Fe 的氧化态

• DOI: 10.1016/j.chemgeo.2024.121937
• 发表时间: 2024-03
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Holycross, Megan;Cottrell, Elizabeth;Ague, Jay;Lanzirotti, Antonio;Newville, Matthew
• 通讯作者: Newville, Matthew

Experimental quantification of vanadium partitioning between eclogitic minerals (garnet, clinopyroxene, rutile) and silicate melt as a function of temperature and oxygen fugacity

榴辉岩矿物（石榴石、单斜辉石、金红石）和硅酸盐熔体之间钒分配随温度和氧逸度变化的实验定量

• DOI: 10.1007/s00410-022-01888-8
• 发表时间: 2022-01-22
• 期刊: Contributions to Mineralogy and Petrology
• 影响因子: 3.5
• 作者: M. Holycross;E. Cottrell
• 通讯作者: E. Cottrell