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

水在地球的行星演化中发挥着独特的作用，特别是在俯冲带。在俯冲带，海洋水循环进入地幔，这是大陆地壳形成的构造环境，引发部分熔融和含水玄武岩的形成，这些玄武岩分化形成大陆地壳，这是我们太阳系内地球所独有的。与含水玄武岩研究相关的众多挑战之一是，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一种镍基橄榄石熔融温度计，该温度计与熔融水含量无关，因此可以应用于含水玄武岩，以获得准确的形成温度。它还将允许在结晶开始时测定玄武岩液体中的水浓度。该项目将聘用两名博士研究生和至少三名本科生，他们将接受各种实验仪器和分析技术的操作以及热力学建模方面的培训；所有这些工具和技能在材料科学中都有重要的应用。该项目将支持一个致力于扩大科学多样性的研究团队中未被充分代表的群体的学生。这项建议的具体目标是在受控的fO2和fH2O条件下，在冷封设备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范围内进行水合相平衡实验，这将使校准这些参数以及熔体组成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，将实验绘制出橄榄石液线的凹陷与熔体水含量(高达？8wt%)的函数关系。一旦有了校准好的温度计和湿度计，它将被应用于来自墨西哥和喀斯喀德火山弧的100块玄武岩，并与橄榄石赋存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，特别是对于含有扩散限制生长结构的橄榄石的天然样品，以及测试在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。

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.