Collaborative Research: Oxygen Fugacity (i.e., Chemical Activity) in the Upper Mantle: Intercalibration of Upper-Mantle Oxybarometers with State-of-the-Art Analytical Techniques

合作研究：上地幔中的氧逸度（即化学活性）：用最先进的分析技术对上地幔氧气压计进行相互校准

• 批准号: 1620276
• 负责人: Jessica Warren
• 金额: $ 16.55万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1620276&HistoricalAwards=false
• 关键词: Collaborative; Research; Oxygen; Fugacity; i.e.

Oxygen is an important element in Earth's mantle and makes up the bulk of most rocks. Its chemical activity (i.e. fugacity) is a controlling factor in determining: (1) the composition of magmas that form from mantle melting, (2) the minerals that are present and in equilibrium with one another in a rock, (3) the distribution of chemical species in associated magmatic fluids, and (4) the partitioning of elements between minerals during their formation and alteration. This research involves a collaboration of three institutions in different parts of the country, employs high temperature/atmospheric-pressure experiments to achieve research goals, and carries out a comparison of the geochemistry of seafloor igneous rocks from the Southwest Indian Ridge. Rock types include mid-ocean ridge basalts, also known as MORB, and abyssal peridotites which represent what is left over in Earth's upper mantle once MORB has been extracted by melting processes. Broader impacts of the work include interaction between scientists from universities and the Smithsonian Museum of Natural History, methods development that advances the infrastructure for science, and a strong integration of research and education. The project will involve the cross-training of a female PhD student who will travel between three laboratories and be trained in state-of-the-art geochemical analytical techniques, providing her with outstanding professional development and networking opportunities. Training of undergraduate students and a postdoc will also take place. The project supports three female researchers, one of whom is early career, and another who is from an institution in an EPSCoR (Experimental Program to Stimulate Competitive Research) state (Rhode Island). The researchers will use the Smithsonian public outreach engine to help implement and promote hands-on learning activities with seafloor rocks where the scientists interact directly with the public. The Smithsonian will also host and disseminate associated online mini-lessons. This research involves petrologic, petrographic, and experimental work to examine the oxygen fugacity of the upper mantle and its variability. Rock samples come from an area of the seafloor that has an exceptional abundance of both basaltic and peridotitic material in close proximity. Most samples have already been well characterized analytically for major and trace elements and key radiogenic isotopes, allowing the research to focus on oxygen fugacity in a more efficient way. The research includes the cross-calibration of the two most frequently used oxybarometers in upper mantle studies: (1) oxygen fugacity determined from Fe3+/Total Fe ratios of mid-ocean ridge basalts determined by XANES, X-ray Absorption Near Edge Structure, spectroscopy and (2) oxygen fugacity derived from electron microprobe measurements of peridotite using Mossbauer-calibrated spinel standards. Because alteration can significantly impact oxybarometer signatures, its effects will be examined by comparing oxygen fugacity results of fresh and altered peridotites that have undergone various degrees of alteration. Experiments will be performed at 1 atm in a vertical gas mixing furnace at a range of oxygen fugacities that bracket the QFM (Quartz, Forsterite, Magnetite) buffer at a range of temperatures to 1225 C. Project goals include: (1) determining the oxygen fugacity of the upper mantle, (2) examining the processes that control the fugacity of oxygen in MORB and abyssal peridotite, and (3) trying to understand over what length scale oxygen fugacity in the mantle varies.

氧是地幔中的重要元素，构成了大多数岩石的主体。其化学活性（即逸度）是决定以下因素的控制因素：(1) 地幔熔化形成的岩浆成分，(2) 岩石中存在且相互平衡的矿物，(3) 相关岩浆液中化学物质的分布，以及 (4) 矿物形成和蚀变过程中元素之间的分配。这项研究涉及该国不同地区的三个机构的合作，采用高温/常压实验来实现研究目标，并对西南印度海岭的海底火成岩的地球化学进行了比较。 岩石类型包括洋中脊玄武岩（也称为 MORB）和深海橄榄岩，代表 MORB 通过熔化过程提取后地球上地幔中残留的物质。 这项工作的更广泛影响包括大学和史密森自然历史博物馆科学家之间的互动、推进科学基础设施的方法开发以及研究和教育的紧密结合。该项目将涉及对一名女博士生进行交叉培训，她将在三个实验室之间往返，并接受最先进的地球化学分析技术的培训，为她提供出色的专业发展和交流机会。还将对本科生和博士后进行培训。该项目支持三名女性研究人员，其中一名处于职业生涯早期，另一名来自 EPSCoR（刺激竞争性研究实验计划）州（罗德岛州）的一个机构。 研究人员将使用史密森尼公共外展引擎来帮助实施和促进海底岩石的实践学习活动，科学家们可以在这些活动中直接与公众互动。 史密森尼还将主办和传播相关的在线迷你课程。 这项研究涉及岩石学、岩石学和实验工作，以检查上地幔的氧逸度及其变化性。 岩石样本来自海底区域，该区域附近富含玄武岩和橄榄岩物质。 大多数样品已经对主要元素和微量元素以及关键放射性同位素进行了良好的分析表征，从而使研究能够以更有效的方式集中于氧逸度。 该研究包括上地幔研究中两种最常用的氧气压计的交叉校准：(1) 根据 XANES、X 射线吸收近边缘结构、光谱确定的大洋中脊玄武岩的 Fe3+/总铁比确定的氧逸度，以及 (2) 使用穆斯堡尔校准尖晶石对橄榄岩进行电子探针测量得出的氧逸度 标准。由于蚀变会显着影响氧压计特征，因此将通过比较经历了不同程度蚀变的新鲜橄榄岩和蚀变橄榄岩的氧逸度结果来检查其影响。实验将在 1 atm 的立式气体混合炉中进行，其氧逸度范围涵盖 QFM（石英、镁橄榄石、磁铁矿）缓冲器，温度范围可达 1225 C。项目目标包括：(1) 确定上地幔的氧逸度，(2) 检查控制 MORB 和深海氧逸度的过程。 橄榄岩，以及（3）试图了解地幔中氧逸度的变化范围。