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”。矿物的氧同位素组成（18O/16O比值）与形成矿物的水的氧同位素组成（18O/16O比值）的差异提供了精度为~1°C的温度估计。将这种方法应用于古代样本的问题在于，水——通常是海水——没有保存在岩石中，需要推断。这给推导出的古地温估计带来了一些不确定性。也就是说，矿物形成时海水的氧同位素组成和现在一样吗？几十年来，研究人员一直在研究这个问题，但仍未得到解决。在这项提议中，该团队将使用一种前所未有的新技术，即使用所有三种天然存在的氧同位素来测定温度。长期以来，人们一直认为稀有同位素17O对通常测量的18O/16O比值没有提供额外的信息。最近，该团队和其他研究小组已经表明，温度对18O/16O和17O/16O比率的影响存在细微差异。通过精确测量16O、17O和18O这三种同位素，可以消除仅使用18O/16O比率所固有的不确定性。该奖项将帮助支持两名学生的毕业论文，其中一名是女性，另一名是少数民族。它还将为本科生提供研究机会，使他们能够亲自使用先进的实验室设备。这样的机会对有潜力的年轻科学家来说是无价的。研究者和研究生都将在这个项目的三年时间框架内与本科生密切合作。这是一个新的研究途径，有许多悬而未决的问题。作为我们研究的一部分，他们将通过在高温高压下实验平衡石英-水混合物，校准石英和水的18O/16O和17O/16O比例对温度的依赖。他们将把这项技术的初步试验扩展到非常重要的矿物方解石。海洋碳酸盐在岩石记录中无处不在，如果这种方法对方解石有效，将极大地扩大这种新技术的研究潜力。不幸的是，方解石的17O/16O比分析已被证明是非常困难的。该研究小组最初将花时间进行分析测试，以量化该测量结果，并将其复制为标准。一旦方法得到进一步确立，他们将继续分析一些最原始的古代样本，以测试这个古老的问题：“古代海水的氧同位素组成是否与今天一样？”同时，他们将把这项工作应用于高温系统，作为在热液系统中检索温度和流体成分（来源）的一种方式。这项工作将对经济地质界有重要的应用，他们努力了解矿藏是如何形成的。

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.