Calibration of Cosmogenic Argon Production Rates in Antarctica

南极洲宇宙源氩生产率的校准

• 批准号: 0125194
• 负责人: Paul Renne
• 金额: $ 24.47万
• 依托单位: Berkeley Geochronology Center
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125194&HistoricalAwards=false
• 关键词: Calibration; Cosmogenic; Argon; Production; Rates

0125194RenneThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for research to establish the systematics of cosmogenic argon production necessary to establish its measurement as a routine surface exposure dating tool analogous to existing methods based on 3He, 10Be, 14C, 21Ne, and 26Al. Cosmogenic argon offers advantages over existing cosmogenic chronometers in that it is stable (hence applicable to long-term or ancient exposure dating) and less prone to diffusive loss than He or Ne. Production of 38Ar is principally by spallation of Ca and (probably) K, and is most easily measured using neutron-irradiated samples as has been performed routinely on extraterrestrial samples for several decades. Initial measurements on Antarctic samples by the principal investigators demonstrate the viability of this method for terrestrial samples, and suggest an average production rate 100 atoms/gm-Ca/year. Existing data suggest that 38Ar/Ca exposure ages younger than 10^5 years may be determined by this method with useful accuracy. Further work on calcic minerals (apatite, sphene, clinopyroxene, plagioclase, calcite) whose exposure histories are constrained by 3He and 21Ne concentration data, will be used to determine the Ca-derived production rate. Analogous work on K-rich minerals (K-feldspars, micas) will be used to constrain the production of 38Ar from K, which should theoretically be comparable to that from Ca, using the same neutron-activation method. The analytical work will use existing samples plus new samples to be collected from the Dry Valleys of Antarctica in order to maximize cosmic radiation dosage for calibration purposes. Laboratory studies of 38Ar retentivity in appropriate minerals will be used to help evaluate our results and guide future applications. The results of this work will be important to a wide array of investigations that require knowledge of surface exposure ages.

0125194 Renne该奖项由极地计划办公室南极地质和地球物理计划提供，为研究建立宇宙成因氩生产的系统学提供资金，以建立其测量作为常规表面暴露测年工具，类似于基于3 He，10 Be，14 C，21 Ne和26 Al的现有方法。宇宙成因氩比现有的宇宙成因计时器具有优势，因为它是稳定的（因此适用于长期或古老的暴露年代测定），并且比He或Ne更不容易扩散损失。38 Ar的产生主要是由Ca和（可能）K的溅射产生的，并且最容易使用中子辐照样品进行测量，因为几十年来一直在对外星样品进行常规测量。主要研究人员对南极样品的初步测量表明，这种方法对陆地样品是可行的，并建议平均生产率为100原子/克钙/年。现有的数据表明，用这种方法可以确定小于10^5年的38 Ar/Ca暴露年龄，具有有用的精度。对暴露历史受3 He和21 Ne浓度数据约束的钙质矿物（磷灰石、斜辉石、单斜辉石、斜长石、方解石）的进一步研究将用于确定钙衍生的生产率。类似的工作，对富钾矿物（钾晶石，云母）将被用来限制生产的38 Ar从K，这在理论上应该是可比的，从Ca，使用相同的中子活化方法。分析工作将使用现有的样品和从南极洲干谷收集的新样品，以便最大限度地提高用于校准目的的宇宙辐射剂量。在适当的矿物中的38 Ar保持性的实验室研究将用于帮助评估我们的结果和指导未来的应用。这项工作的结果将是重要的调查，需要了解表面暴露年龄的广泛。