Improving the 40Ar/39Ar geochronometer

改进 40Ar/39Ar 地球计时仪

• 批准号: 2102788
• 负责人: Paul Renne
• 金额: $ 50.63万
• 依托单位: Berkeley Geochronology Center
• 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: 2021-08-15 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2102788&HistoricalAwards=false
• 关键词: Improving; 40Ar; 39Ar; geochronometer

This project aims to significantly improve the accuracy of the 40Ar/39Ar and K-Ar dating methods. Both of these methods are based on the natural radioactive decay of potassium, a common element in rocks and other geological materials. These methods are among the most important methods for dating events in Earth, planetary and biological history because they can be applied to diverse materials and their effective time range of applicability is the greatest of any such method. However, despite excellent and continually improving precision, i.e., experimental reproducibility, these methods are limited in accuracy by how well the decay constants are known, as well as the isotope composition of standards needed for calibration. Thus, while 40Ar/39Ar and K-Ar dating can resolve small age differences and precisely determine rates of geological processes, comparing their results with age data from other methods (e.g., radiocarbon or U-Pb) is only valid at the 1% level at best. The improvements to be realized in this project will benefit the fields of geology, geophysics, paleontology (including paleoanthropology), archeology, and planetary science.The project will combine measurements of 40K and 40Ar concentration in selected standards using K isotopic and concentration measurements by Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) and Thermal Ionization Mass Spectrometry (TIMS), and 40Ar concentration measurements using a purpose-built pipette system and noble gas mass spectrometry. The 40K decay constant will be determined both by ingrowth experiments using highly 40K-enriched potassium in strategically-designed synthetic matrix, and by disintegration activity measurements via liquid scintillation counting. These measurements will allow for new determinations of the isotope composition of primary mineral standards used in 40Ar/39Ar geochronology, and the 40K decay constant. The ingrowth-based decay constant measurement requires an estimated ten years to accumulate sufficient 40Ar for adequately precise measurement, hence exacting preparation of glasses as starting material will be the focus of the present proposal. Many of the activities will be conducted in specialized laboratories overseen by colleagues with relevant expertise. Much of the data acquisition and sample preparation will be conducted by a postdoctoral researcher who will be jointly supervised by PI’s Renne and Morgan. The postdoc will gain broad experience in mass spectrometry, experimental petrology, and nuclear chemistry, and will also gain significant experience in the 40Ar/39Ar laboratories in Berkeley and the US Geological Survey (Denver).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.

该项目旨在显着提高 40Ar/39Ar 和 K-Ar 测年方法的准确性，这两种方法均基于钾的自然放射性衰变，钾是岩石和其他地质材料中的常见元素。测定地球、行星和生物历史事件的重要方法，因为它们可以应用于多种材料，并且它们的有效适用时间范围是所有此类方法中最大的。然而，尽管这些方法具有出色且不断提高的精度（即实验再现性），方法由于衰变常数的已知程度以及校准所需的标准同位素组成，准确度受到限制。因此，虽然 40Ar/39Ar 和 K-Ar 测年可以解决微小的年龄差异并精确确定地质过程的速率，但比较。他们的结果与其他方法（例如放射性碳或 U-Pb）的年龄数据最多仅在 1% 的水平上有效。该项目中要实现的改进将有利于地质学、地球物理学、古生物学（包括古人类学）、考古学和行星科学。该项目将使用 K 同位素对选定标准中的 40K 和 40Ar 浓度进行测量，并通过多接收器电感耦合等离子体质谱 (MC-ICP-MS) 和热电离质谱进行浓度测量(TIMS) 和 40Ar 浓度测量，使用专用移液器系统和惰性气体质谱仪。 40K 衰变常数将通过在精心设计的合成基质中使用高度 40K 富集的钾的向内生长实验以及通过液体闪烁计数的崩解活性测量来确定。这些测量将允许对用于初级矿物标准的同位素组成进行新的测定。 40Ar/39Ar 地质年代学和 40K 衰变常数 基于向内生长的衰变常数测量需要估计十年才能积累足够的 40Ar 来进行足够精确的测量，因此。严格制备玻璃作为起始材料将是本提案的重点，许多活动将在具有相关专业知识的同事的监督下进行，大部分数据采集和样品制备将由博士后研究员进行。博士后将在 PI 的 Renne 和 Morgan 的共同指导下获得质谱、实验岩石学和核化学方面的丰富经验，还将在伯克利和美国地质大学的 40Ar/39Ar 实验室获得重要经验。调查（丹佛）。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。