EAGER: Collaborative Research: Developing new laser ablation (U-Th)/(He-Pb) hematite double dating techniques to date ancient oxidation

EAGER：合作研究：开发新的激光烧蚀 (U-Th)/(He-Pb) 赤铁矿双重测年技术来测定古代氧化的年代

• 批准号: 2203532
• 负责人: Rebecca Flowers
• 金额: $ 8.02万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-12-15 至 2023-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2203532&HistoricalAwards=false
• 关键词: EAGER; Collaborative; Research; Developing; new

This project is focused on improving methods that Earth scientists can use to determine the formation age of the mineral hematite. Hematite is a wide-spread mineral in rocks and soils and often forms due to oxidation on Earth’s surface as well as on other planets — notably Mars. Hematite can incorporate uranium when it forms. Given that uranium undergoes radioactive decay it is possible to conduct both uranium-lead dating (U-Pb) and uranium-thorium-helium dating ((U-Th)/He) on hematite crystals. Investigators will apply methods that can make these measurements simultaneously at a small scale on hematite crystals by blasting them with a laser and measuring the isotopes through mass spectrometry. An additional property of hematite is that it records the magnetic field at the time it crystallizes. This ability to record the ancient magnetic field enables Earth scientists to reconstruct the past position of Earth’s continents and can also be used to gain insight into the timing of hematite formation. They will make magnetic measurements of hematite including measurements that use new capabilities to make magnetic maps at the microscopic scale using an instrument called a quantum diamond microscope. The study will focus on hematite within ancient sedimentary rocks known as iron formations. In the United States, iron formations in the Lake Superior region are the major source of domestic iron production. By applying these dating methods to iron formation, they will constrain the timing of hematite formation in these units, where the timing of oxidation (that is, hematite formation) is debated. If this project is successful, these combined methods of measuring the age of hematite will enable a multitude of future studies. For example, it would be possible to pursue more advanced studies on hematite formation within iron formation, to study the processes and timescales of deep soil leaching (also known as laterization), and determine the timing of ancient surface exposure and chemical alteration in far greater detail using these combined methods. The project will support the research of an early-career scientist, advance development of new analytical capabilities at both University of Carlifornia Berkeley and University of Colorado Boulder, and support both undergraduate and graduate student research for first-generation students.These investigators seek to develop simultaneous in situ laser ablation (U-Th)/He and U-Pb dating of hematite, which is termed LA-(U-Th)/(He-Pb). Although bulk (U-Th)/He and in situ (U-Pb) methods have been used previously on hematite, the coupled laser-ablation technique has never been applied. This method can provide a powerful tool for assessing the timing of oxidation and weathering in a wide range of hematite-bearing environments. Researchers will investigate the timing of hematite crystallization in Lake Superior region iron formation through this method development in conjunction with paleomagnetic data, which can provide complementary chronologic insight. They will focus on a carefully selected set of samples that will enable method development and give new insights into the origin of iron formations. All samples will be characterized prior to geochronologic measurements via electron backscatter diffraction and electron microprobe to understand the chemical heterogeneity of the samples and the distribution of crystallites within hematite aggregates. This characterization will permit targeting of individual crystallites through LA-(U-Th)/(He-Pb) and provide context relative to potential polycrystalline diffusion behavior. This study has two main sample targets: (1) large, high-purity hematite samples from iron formation that will be used for method development; (2) typical iron formation from the Menominee Group. Menominee Group samples will be analyzed through both LA-(U-Th)/(He-Pb) and paleomagnetism. Paleomagnetic analyses will be conducted at both the centimeter and micrometer scale to constrain hematite formation relative to folding and through comparison to Laurentia’s apparent polar wander path. The well-constrained regional history of deposition, tectonism, and near-surface weathering provides testable hypotheses for the timing of hematite formation in these samples. Successful radiometric dating of these materials will provide confidence in the utility of the LA-(U-Th)/(He-Pb) method in natural samples beyond museum-quality hematite specimens.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.

该项目的重点是改进地球科学家可以用来确定矿物赤铁矿的形成年龄的方法。赤铁矿是岩石和土壤中的广泛矿物，由于地球表面以及其他行星（尤其是火星）的氧化而经常形成。赤铁矿形成时可以掺入铀。鉴于铀经历放射性衰变，可以在赤铁矿晶体上同时进行铀铅约会（U-PB）和铀硫螺旋约会（（u-th）/He）。研究人员将采用可以通过用激光器爆炸并通过质谱测量同位素来简单地在赤铁矿晶体上以小尺度进行这些测量的方法。赤铁矿的另一个特性是它在结晶时记录了磁场。这种记录古代磁场的能力使地球科学家能够重建地球大陆的过去位置，还可以用来深入了解赤铁矿形成的时机。他们将对赤铁矿进行磁测量，包括使用新功能使用称为量子钻石显微镜的仪器在显微镜尺度上制作磁图的测量值。该研究将集中在古代沉积岩中的赤铁矿上，称为铁地层。在美国，苏必利尔湖地区的铁地层是国内铁生产的主要来源。通过将这些约会方法应用于铁的形成，它们将限制在这些单位中赤铁矿形成的时机，在这些单位中，在争论氧化的时间（即赤铁矿形成）。如果该项目成功，那么测量赤铁矿年龄的这些组合方法将实现多种未来的研究。例如，有可能在铁形成中进行有关赤铁矿形成的更多高级研究，以研究深层漫步的过程和时间尺度（也称为延迟化），并使用这些合并的方法确定古代表面暴露和化学改变的时机。 The project will support the research of an early-career scientist, advance development of new analytical capabilities at both University of Carlifornia Berkeley and University of Colorado Boulder, and support both undergraduate and graduate student research for first-generation students.These investigators seek to develop simultaneous in situ laser ablation (U-Th)/He and U-Pb dating of hematite, which is termed la-（u-th）/（He-pb）。尽管散装（u-th）和原位（u-pb）方法先前已在赤铁矿上使用，但耦合的激光燃料技术从未应用。这种方法可以提供一种强大的工具，用于评估氧化和风化的时机在宽阔的范围内血流范围。研究人员将通过这种方法开发与古磁数据一起研究苏里湖地区铁形成的赤铁矿结晶的时间，这可以提供完全的时间顺序洞察。他们将专注于一组精心选择的样本，这些样本将启用方法开发，并提供有关铁层的起源的新见解。所有样品将在通过电子反向散射和电子微型探针进行测量学测量之前进行表征，以了解样品的化学异质性以及赤铁矿聚集体内的油晶分布。该表征将允许通过LA-（u-th）/（He-pb）靶向单个微晶，并提供相对于潜在多晶扩散行为的背景。这项研究有两个主要的样本靶标：（1）将用于方法开发的铁形成中的大型高纯性赤铁矿样品； （2）Menominee组的典型铁形成。将通过LA-（U-TH）/（HE-PB）分析Menominee组样品，并将在厘米和千分尺尺度上进行古磁分析，以约束赤铁矿形成相对于折叠的形成，并与Laurentia的显而易见的极性徘徊路径进行比较。沉积，构造和近地表风化的区域历史良好，为这些样品中赤铁矿形成的时间提供了可检验的假设。这些材料的成功辐射测定将对La-（u-th）/（He-pb）方法的实用性提供信心，而在博物馆质量的赤铁矿标本以外的天然样本中。该奖项反映了NSF的法定任务，并被认为是通过基金会的智力优点和更广泛的影响审查的审查标准来通过评估来通过评估来获得的支持。