Significant improvements in the development and application of olivine-melt thermometry and hygrometry: new experiments and analytical approaches

该奖项部分由2021年美国救援计划法案（公法117-2）资助。地球历史上的玄武岩火山活动深刻地塑造了地壳和大气的演变，以及生命本身的进化路径。在这项研究中，喷发的玄武岩被用作研究它们形成的底层地幔的窗口。目标是开发一种新的温度计/湿度计，使玄武岩的温度和含水量都能容易和准确地获得。它的易用性将有助于生成大型数据集，这将使人们能够解决来自不同构造环境和整个地球历史的玄武岩的全球差异问题。新的温度计/湿度计将提供给所有感兴趣的用户作为可下载的excel文件。两名来自不同背景的澳大研究生将参与这个项目。他们将获得广泛的技能，从进行高温高压实验的专业知识，执行热力学计算，以及应用他们的结果来更好地约束导致部分熔化的地幔条件。此外，密歇根大学（UM） M-STEM项目的本科生将被招募参与该项目。本项目的目标是继续对一种新的基于橄榄石和玄武岩液体（DNiol/liq）之间镍分配的橄榄石熔体温度计（DNiol/liq）进行实验校准，并进一步测试它是否独立于地壳和地幔深度的溶解水。目前，最广泛使用的橄榄石熔体温度计（基于DMgol/liq）强烈依赖于水，它们在含水玄武岩上的应用要求已经知道熔体水的浓度，但情况并非总是如此。手头有一个基于DNiol/liq的不依赖于h2o的温度计，它可以应用于含水玄武岩中的橄榄石斑晶，以获得准确的温度，而无需事先了解熔体含水量。然后，这些温度可以与基于镁的橄榄石熔体温度计结合，以获得无水温度，从而得到∆T的大小，即橄榄石液态液由于溶解的水而下降的幅度。将进行实验来评估这种由水引起的橄榄石液相的下降是否与橄榄石和熔体之间Ca的分配（DCaol/liq）呈线性和负相关，正如初步工作所表明的那样。为了扩展这种新的橄榄石熔体温度计/湿度计的校准，将在一系列含水量、温度、压力（地壳和地幔）和fO2条件下对各种玄武岩成分进行实验。此外，还建议将这种新的温度计/湿度计应用于大量来自不同构造背景的天然玄武岩。这些结果将揭示在从俯冲带到地幔柱到大陆裂谷的各种构造环境中，地幔部分融化期间的热/水条件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Basaltic volcanism throughout Earth history has profoundly shaped the evolution of Earth’s crust and atmosphere, as well as the evolutionary path of life itself. In this study, erupted basalts are used as windows into the underlying mantle from which they were formed. The goal is to develop a new thermometer/hygrometer that enables both the temperature and water content of basalts to be readily and accurately obtained. Its ease of use will help generate large data sets, which will allow questions to be addressed about global differences in basalts erupted from diverse tectonic settings and throughout Earth history. The new thermometer/hygrometer will be made available to all interested users as a downloadable excel file. Two UM graduate students from diverse, under-represented backgrounds will work on this project. They will gain a broad range of skills, from expertise in conducting high-temperature and high-pressure experiments, performing thermodynamic calculations, and applying their results to better constrain mantle conditions that lead to partial melting. In addition, undergraduates from the M-STEM program at the University of Michigan (UM) will be recruited to work on this project.The goal of this project is to continue the experimental calibration a new olivine-melt thermometer that is based on the partitioning of Ni between olivine and basaltic liquids (DNiol/liq), and to further test whether it is independent of dissolved water at both crustal and mantle depths. Currently, the most widely used olivine-melt thermometers (based on DMgol/liq) are strongly dependent on water, and their application to hydrous basalts requires that melt H2O concentrations already be known, which is not always the case. With an H2O-independent thermometer in hand, based on DNiol/liq, it can be applied to olivine phenocrysts in hydrous basalts to obtain accurate temperatures, without prior knowledge of melt water contents. These temperatures can then be combined with Mg-based olivine-melt thermometers to obtain anhydrous temperatures and thus the magnitude of ∆T, the depression of the olivine liquidus due to dissolved water. Experiments will be performed to evaluate whether this depression of the olivine liquidus due to water is linearly and inversely correlated with the partitioning of Ca between olivine and melt (DCaol/liq), as indicated in preliminary work. To extend the calibration of this new olivine-melt thermometer/hygrometer, experiments will be performed on a variety of basaltic compositions over a range of water contents, temperatures, pressures (crustal and mantle) and fO2 conditions. Additionally, it is proposed to apply the new thermometer/hygrometer to a large number of natural basalts from a variety of tectonic settings. The results will shed light on the thermal/hydrous conditions in the mantle during partial melting across a variety of tectonic settings, from subduction zones to mantle plumes to continental rifts.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.