Experimental Calibration of Inter-mineral Magnesium and Iron Isotope Fractionation at High Temperatures

高温矿间镁铁同位素分馏的实验校准

• 批准号: 1524811
• 负责人: Edward Young
• 金额: $ 33万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-01 至 2022-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524811&HistoricalAwards=false
• 关键词: Experimental; Calibration; Inter; mineral; Magnesium

Isotopes of common rock-forming elements have great potential for understanding the redistribution of mass during geological processes. In order to make use of these isotopes one must know how they partition between different minerals in the rocks. Two of the most important elements of interest to the geological community are magnesium (Mg) and iron (Fe). This group proposes to build on their previous experimental program to test and augment theoretical predictions for iron and magnesium isotope partitioning between mineral phases at high temperatures. The project represents an uncommon integration of experimental petrology and isotope geochemistry. The investigators have trained three graduate students in recent years, two of whom are women, an underrepresented demographic in the geological sciences.Iron and magnesium are targeted for this interdisciplinary study because of their importance as rock-forming elements and recent indications that these elements may be more mobile in Earth's mantle than previously thought. Indeed, there has been an explosion of studies on the distributions of these isotopes in natural samples. The focus of this study is on Fe and Mg isotope fractionation between spinels and other phases. Spinels are of interest because there is more than one coordination site for these cations in the spinel structure, affording tests of the principles of stable isotope partitioning. Experiments will be performed in a piston cylinder apparatus. The group will use the three-isotope method to establish equilibrium fractionation factors in these two isotope systems. This method involves spiking one of the phases with an excess of the abundant isotope in order to disturb the usual state of mass-dependent fractionation among three isotopes in the experiments. This mass fractionation relationship among the three isotopes is a necessary condition for equilibrium. The drive towards reestablishment of that condition during the experimental run is used as a monitor for isotope exchange in the experiments. The team will investigate equilibrium Mg isotope fractionation between Mg(Al,Cr)2O4 spinels and forsterite olivine and equilibrium Fe isotope fractionation between almandine garnet and magnetite (an inverse spinel). Results of the latter experiments can be combined with previous experiments to arrive at temperature-dependent garnet-olivine iron isotope fractionation factors. Both systems are pivotal in the interpretation of natural Mg and Fe isotope data.

共同岩石形成元件的同位素具有理解地质过程中质量重新分布的巨大潜力。 为了利用这些同位素，必须知道它们如何在岩石中的不同矿物之间进行分配。 地质界最重要的两个要素是镁（MG）和铁（FE）。 该小组提议建立在他们先前的实验计划的基础上，以测试和增强高温下矿物相之间的铁和镁同位素分配的理论预测。 该项目代表了实验质学和同位素地球化学的罕见整合。近年来，研究人员对三名研究生进行了培训，其中两名是女性，是地质科学中代表性不足的人群。这项跨学科研究的目标是针对这项跨学科研究，因为它们作为岩石形成元素的重要性，并且最近的迹象表明，这些元素在地球上可能比以前的地幔更具移动性。 实际上，关于这些同位素在天然样品中的分布的研究已经爆炸。 这项研究的重点是尖晶石和其他阶段之间的FE和MG同位素分馏。 尖晶石引起了人们的关注，因为这些阳离子在尖晶石结构中有一个以上的协调位点，可对稳定的同位素分配原理进行测试。 实验将在活塞缸设备中进行。 该组将使用三异位方法在这两个同位素系统中建立平衡分级因子。 该方法涉及在实验中三个同位素之间的质量依赖性分馏的常见状态，以跨越大量同位素的峰值。 三个同位素之间的这种质量分馏关系是平衡的必要条件。 在实验运行期间重建该状况的动力被用作实验中同位素交换的监视器。 该小组将研究Mg（Al，Cr）2O4尖晶石和脚石橄榄石和Almandine Garnet和Magnetite（Aneverse Spinel）之间的平衡MG同位素分馏。 后一个实验的结果可以与先前的实验相结合，以达到温度依赖性的石榴石 - 橄榄油同位素分馏因子。 两种系统在解释自然MG和Fe同位素数据的解释中都是关键的。