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

橄榄石熔体测温法和测湿法的开发和应用的重大改进：新实验和分析方法

基本信息

批准号：
2125941
负责人：
Rebecca Lange
金额：
$ 41.47万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-08-01 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2125941&HistoricalAwards=false
关键词：
Significant improvements development application olivine

项目摘要

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.

该奖项的部分资金来源于《2021 年美国救援计划法案》（公法 117-2）。整个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观察形成玄武岩的底层地幔的窗口。目标是开发一种新型温度计/湿度计，能够轻松准确地获得玄武岩的温度和含水量。它的易用性将有助于生成大型数据集，从而解决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该项目。他们将获得广泛的技能，包括进行高温高压实验、进行热力学计算以及应用其结果更好地限制导致部分熔化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来从事该项目。该项目的目标是继续实验校准一种新的橄榄石熔体温度计，该温度计基于橄榄石和玄武岩液体（DNiol/liq）之间Ni的分配，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体温度计（基于 DMgol/liq）强烈依赖于水，并且它们在含水玄武岩中的应用要求已知熔体 H2O 浓度，但情况并非总是如此。有了基于 DNiol/liq 的独立于 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，而无需事先了解融水含量。然后可以将这些温度与基于镁的橄榄石熔体温度计相结合，以获得无水温度，从而获得 ΔT 的大小，即由于溶解水而导致的橄榄石液相线的下降。将进行实验来评估由于水导致的橄榄石液相线降低是否与橄榄石和熔体 (DCaol/liq) 之间的 Ca 分配呈线性负相关，如初步工作所示。为了扩展这种新型橄榄石熔体温度计/湿度计的校准，将对各种玄武岩成分在一系列含水量、温度、压力（地壳和地幔）和 fO2 条件下进行实验。此外，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。研究结果将揭示从俯冲带到地幔柱再到大陆裂谷的各种构造环境部分熔融过程中地幔的热/含水条件。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。