Calibration of Cosmogenic Argon Production Rates in Antarctica

[125194]该奖项由极地计划办公室的南极地质和地球物理计划提供，为建立宇宙生成氩的系统研究提供资金，以建立其测量作为常规表面暴露测年工具，类似于现有的基于3He， 10Be, 14C， 21Ne和26Al的方法。与现有的宇宙生成计时器相比，宇宙生成氩具有稳定的优点（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。38Ar的产生主要是通过Ca和（可能）K的散裂，并且最容易使用中子辐照样品进行测量，就像几十年来在外星样品上常规进行的那样。主要研究人员对南极样品进行的初步测量表明，这种方法对陆地样品是可行的，并表明平均产量为100原子/克-钙/年。现有的数据表明，38Ar/Ca暴露年龄小于10^5年可以用这种方法确定有用的准确性。对暴露历史受3He和21Ne浓度数据限制的钙矿物（磷灰石、榍石、斜长石、方解石）的进一步研究将用于确定钙衍生的产量。对富钾矿物（钾长石，云母）的类似研究将用于限制K产生38Ar，理论上应该与Ca相当，使用相同的中子活化方法。分析工作将使用现有样品和从南极洲干谷收集的新样品，以便最大限度地提高宇宙辐射剂量以进行校准。在适当的矿物中38Ar保留率的实验室研究将用于帮助评估我们的结果并指导未来的应用。这项工作的结果对于需要了解地表暴露年龄的广泛调查将是重要的。

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.