Experimental Calibration of the Olivine-melt Ni Thermometer Under Hydrous Conditions: Applications to Hygrometry, Oxybarometry and Olivine Phenocryst Growth Rates

含水条件下橄榄石熔体镍温度计的实验校准：在湿度测定、氧压测定和橄榄石斑晶生长速率中的应用

• 批准号: 1551344
• 负责人: Rebecca Lange
• 金额: $ 34万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1551344&HistoricalAwards=false
• 关键词: Experimental; Calibration; Olivine; melt; Ni

Water plays a unique role in the planetary evolution of Earth, particularly at subduction zones. The recycling of oceanic water into the mantle at subduction zones, the tectonic setting where continental crust forms, triggers partial melting and the formation of hydrous basalts, which differentiate to form continental crust, unique to Earth within our solar system. One of the many challenges associated with the study of hydrous basalts is that current thermometers cannot be accurately applied to them. The goal of this project is to calibrate a Ni-based olivine-melt thermometer, which is independent of melt water contents and can thus be applied to hydrous basalts to obtain accurate temperatures of formation. It will also allow the concentration of water in basaltic liquids to be determined at the onset of crystallization. This project will engage two Ph.D. graduate students and at least three undergraduate students, who will be trained in the operation of various experimental apparatus and analytical techniques, as well as thermodynamic modeling; all of these tools and skills have important applications in material science. The project will support students from underrepresented groups in a research team that has demonstrated a commitment to expanding the diversity of those in the sciences.The specific goals of this proposal are to perform hydrous phase-equilibrium experiments in a cold-seal apparatus under controlled fO2 and fH2O conditions on a variety of natural basalt and basaltic andesite liquids over a range of temperature and pressure, which will enable calibration of how these parameters, together with melt composition, affect the partitioning of Ni between olivine and liquid. In addition, the depression of the olivine liquidus as a function of melt water content (up to ¡Ü 8 wt%) will be experimentally mapped out for several melt compositions. Once a well-calibrated thermometer and hygrometer are in hand, it will be applied to 100 basalts from the Mexican and Cascades volcanic arcs and compared to results from olivine-hosted melt inclusions. Two additional experimental goals are to measure crystal growth rates of olivine phenocrysts under hydrous melt conditions, especially for natural samples that contain olivine with diffusion-limited growth textures, and to test whether Fe-Mg KD values obtained in hydrous olivine-melt experiments can be used to place constraints on the oxidation state of natural basalts.

水在地球的行星演化中起着独特的作用，特别是在俯冲带。在大陆地壳形成的构造环境中，海水在俯冲带的地幔中循环，引发了部分熔融和含水玄武岩的形成，这些玄武岩分化形成了我们太阳系中地球独有的大陆地壳。与含水玄武岩研究相关的许多挑战之一是，目前的温度计不能准确地应用于它们。该项目的目标是校准镍基橄榄石熔体温度计，该温度计与熔体含水量无关，因此可以应用于含水玄武岩，以获得准确的地层温度。它还可以在结晶开始时测定玄武岩液体中水的浓度。本项目将招收2名博士研究生和至少3名本科生，对他们进行各种实验设备和分析技术的操作以及热力学建模的培训；所有这些工具和技能在材料科学中都有重要的应用。该项目将支持一个研究团队中来自代表性不足群体的学生，该团队已证明致力于扩大科学领域的多样性。本课题的具体目标是在可控的fO2和fH2O条件下，在冷密封装置中对各种天然玄武岩和玄武岩安山岩液体在一定温度和压力下进行水相平衡实验，这将能够校准这些参数以及熔体成分如何影响镍在橄榄石和液体之间的分配。此外，对于几种熔体成分，将通过实验绘制出熔体含水量（高达Ü 8wt %）对橄榄石液相曲线的影响。一旦校准好的温度计和湿度计到手，它将应用于来自墨西哥和喀斯喀特火山弧的100块玄武岩，并与含有橄榄石的熔体包裹体的结果进行比较。另外两个实验目标是测量含水熔体条件下橄榄石斑晶的晶体生长速率，特别是对于含有具有扩散限制生长结构的橄榄石的天然样品，以及测试含水橄榄石熔体实验中获得的Fe-Mg KD值是否可以用于限制天然玄武岩的氧化状态。