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

该奖项的部分资金来自2021年美国救援计划法案(公法117-2)。贯穿地球历史的玄武岩火山活动深刻地塑造了地球地壳和大气的演化，以及生命本身的演化路径。在这项研究中，喷发的玄武岩被用作了解它们形成的下地幔的窗口。其目标是开发一种新的温度计/湿度计，使玄武岩的温度和水含量能够容易和准确地获得。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有关不同构造环境和整个地球历史中喷发的玄武岩的全球差异的问题。新的温度计/湿度计将以可下载的EXCEL文件形式提供给所有感兴趣的用户。两名来自不同背景、代表性不足的密歇根大学研究生将参与这个项目。他们将获得广泛的技能，从进行高温和高压实验、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融的地幔条件的专业知识。此外，密歇根大学(UM)M-STEM项目的本科生将被招募参与这一项目。该项目的目标是继续实验校准一种新的橄榄石熔融温度计，该温度计基于镍在橄榄石和玄武岩液体之间的分配(DNiol/liq)，并进一步测试它是否独立于地壳和地幔深处的溶解水。目前，最广泛使用的橄榄石熔融温度计(基于DMgol/liq)强烈依赖于水，它们对含水玄武岩的应用要求已知熔体H2O浓度，但情况并不总是如此。手头有一个基于DNiol/liq的独立于水的温度计，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，而不需要事先知道熔体的水含量。然后将这些温度与镁基橄榄石熔融温度计相结合，得到无水温度，从而得到∆T的大小，即由于溶解的水而导致的橄榄石液线的下降。将进行实验，以评估水对橄榄石液线的这种抑制是否与钙在橄榄石和熔体之间的分配(DCaol/liq)呈线性和负相关，正如初步工作所表明的那样。为了扩大这个新的橄榄石熔融温度计/湿度计的校准范围，将在不同的水分含量、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，还建议将新的温度计/湿度计应用于来自各种构造环境的大量天然玄武岩。这一结果将揭示从俯冲带到地幔羽流再到大陆裂谷等各种构造环境下部分熔融过程中地幔的热/水条件。这一裁决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智力优势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.