Terrestrial Applications of the Triple Oxygen Isotope Geothermometer

60多年来，天然材料的氧同位素组成一直被用作古代岩石和矿物样品的定量“温度计”。矿物和形成矿物的水的氧同位素组成(18O/16O比值)的差异提供了一个精度为~1°C的温度估计。将这种方法应用于古代样品的问题是，水--通常是海水--不会保存在岩石中，需要进行推断。这给推导出的古温度估计带来了一些模糊性。也就是说，这种矿物形成时海水的氧同位素组成与今天的一样吗？几十年来，研究人员一直在解决这个问题，但至今仍未得到解决。在这项提案中，该团队将使用一种以前从未尝试过的新技术，在这种技术中，所有三个自然产生的氧同位素都用于温度测定。长期以来，人们一直认为稀有同位素17O不会为通常测量的18O/16O比值提供额外的信息。最近，这个团队和其他研究小组表明，温度影响18O/16O和17O/16O比率的方式存在细微差异。通过准确测量16O、17O和18O这三种同位素，建议消除单独使用18O/16O比值所固有的不确定性。这一奖项将帮助资助两名学生的毕业论文，其中一名是女性，另一名是少数民族。它还将包括本科生的研究机会，允许他们亲手接触尖端的实验室设备。这样的机会对年轻的有潜力的科学家来说是无价的。研究人员和研究生都将与在这个项目的三年时间框架内招收的本科生密切合作。这是一个新的研究途径，有许多突出的问题。作为我们研究的一部分，他们将通过实验在高温和高压下平衡石英-水混合物，来校准石英和水的18O/16O和17O/16O比率对温度的依赖关系。他们将把这项技术的初步试验扩大到非常重要的矿物方解石。海相碳酸盐在岩石记录中随处可见，如果这种方法适用于方解石，将极大地扩展这项新技术的研究潜力。不幸的是，方解石对17O/16O比值的分析已被证明是非常困难的。该研究小组最初将花费时间进行分析测试，以量化这一测量并将其复制为标准。一旦方法进一步确立，他们将继续分析一些最原始、最古老的样本，以检验一个古老的问题：古代海水的氧同位素组成与今天一样吗？同时，他们将把这项工作应用于高温系统，作为一种恢复水热系统中温度和流体成分(源)的方法。这项工作将对努力了解矿藏形成的经济地质界有重要的应用。

The oxygen isotope compositions of natural materials have been used for over 60 years as a quantitative 'thermometer' for ancient rock and mineral samples. The difference in the oxygen isotope composition (the 18O/16O ratio) of a mineral and the water from which it formed provides a temperature estimate that has a precision of ~1°C. The problem with application of this method to ancient samples is that the water - usually ocean water - is not preserved in the rock and needs to be inferred. This introduces some ambiguity to the derived paleotemperature estimate. Namely, was the oxygen isotope composition of the ocean water at the time the mineral formed the same as it is today? Researchers have been tackling this question for decades, and it is still unresolved. In this proposal, the team will use a novel, previously untried, technique in which all three naturally occurring oxygen isotopes are used for temperature determinations. It has long been thought that the rare isotope 17O provides no additional information to the commonly measured 18O/16O ratios. More recently, this team and other research groups have shown that there are subtle differences in the way temperature affects the 18O/16O and 17O/16O ratios. By accurately measuring all three isotopes, 16O, 17O and 18O, it is proposed to eliminate the uncertainties inherent in using the 18O/16O ratios alone. This award will help support the graduate theses of two students, one of whom is a woman, the other a minority. It will also include research opportunities for an undergraduate student, allowing them hands-on access to sophisticated laboratory equipment. Such an opportunity is invaluable for young potential scientists. Both the investigator and the graduate students will work closely with undergraduate students recruited over the three year time frame of this project. This is a new research avenue and there are many outstanding questions. As part of our research, they will calibrate the temperature dependence on the 18O/16O and 17O/16O ratios of quartz and water by experimentally equilibrating a quartz-water mixture at high temperatures and pressures. They will expand the preliminary tests of the technique to the very important mineral calcite. Marine carbonates are ubiquitous in the rock record, and if the approach works for calcite it will vastly expand the research potential of this new technique. Unfortunately, the analysis of calcite for 17O/16O ratios has proven to be very difficult. This research group will initially spend time conducting analytical tests to quantifying this measurement and reproduce it for a standard. Once the methodology is further established, they will proceed to analyze some of the most pristine, ancient samples in order to test the age-old question 'Is the oxygen isotope composition of ancient seawater the same as it is today?' At the same time, they will apply this work to high temperature systems as a way of retrieving both temperatures and fluid compositions (sources) in hydrothermal systems. This work will have important applications to the economic geology community which strives to understand how mineral deposits form.