Calibration of Cosmogenic Argon Production Rates in Antarctica

这个奖项由极地方案办公室的南极地质和地球物理方案提供，为建立宇宙成因的Ar产生的系统学提供研究资金，以建立其测量作为一种常规的表面暴露测年工具，类似于现有的基于3He、10Be、14C、21Ne和26Al的方法。宇宙成因的Ar比现有的宇宙成因计时器具有优势，因为它稳定(因此适用于长期或古代曝光测年)，并且比He或Ne更不容易扩散损失。38Ar的产生主要是通过钙和(可能)K的散裂产生的，最容易测量的是使用中子辐照的样品，就像几十年来在地外样品上常规进行的那样。主要调查人员对南极样本的初步测量表明，这种方法对陆地样本是可行的，并建议平均产生100个原子/克-钙/年。现有数据表明，用这种方法可以准确地确定小于10^5岁的38Ar/Ca暴露年龄。对暴露历史受3He和21Ne浓度数据制约的钙质矿物(磷灰石、辉石、单斜辉石、斜长石、方解石)的进一步工作将用于确定钙的产生率。对富钾矿物(钾长石、云母)的类似工作将被用来限制从K中产生38Ar，理论上应该与从Ca中产生的38Ar相当，使用相同的中子激活方法。分析工作将使用现有样品以及从南极洲干燥山谷收集的新样品，以最大限度地增加用于校准目的的宇宙辐射剂量。对38Ar在适当矿物中的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。这项工作的结果将对需要了解表面暴露年龄的广泛调查具有重要意义。

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.