Cho Yuichiro, Cohen Barbara A
NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, 20771, USA.
University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD, 21250, USA.
Rapid Commun Mass Spectrom. 2018 Oct 30;32(20):1755-1765. doi: 10.1002/rcm.8214.
We report new K-Ar isochron data for two ~380 Ma basaltic rocks, using an updated version of the Potassium-Argon Laser Experiment (KArLE), which is being developed for future in situ dating of planetary materials. These basalts have K contents comparable with those of lunar KREEP basalts or igneous lithologies found by Mars rovers, whereas previous proof-of-concept studies focused primarily on more K-rich rocks. We aim to measure these analogous samples to show the advancing capability of in situ K-Ar geochronology.
Combining laser-induced breakdown spectroscopy (LIBS), mass spectrometry (MS), and microscopic analyses, we measured the abundance of K and Ar from 23 spots on the basalt samples. We then constructed K-Ar isochron plots from these rocks. The breadboard instrument consists of flight-equivalent devices including a 30-mJ Nd:YAG laser and a quadrupole mass spectrometer.
Despite much lower K abundances than in previous studies, the isochron slopes yielded 380 ± 44 Ma and 398 ± 50 Ma for 380.7-Ma and 373.5-Ma rocks, respectively, indicating that accuracy better than 25 Ma (<7%) is achievable with our instrument. The isochron intercepts both yielded trapped Ar approximately 1 × 10 cm STP/g.
Our experimental results demonstrate that accurate and precise measurements are possible using the KArLE approach on basaltic rocks, which are ubiquitous on planetary surfaces, and are useful in addressing a wide range of questions in planetary science.
我们报告了两块约3.8亿年历史的玄武岩的新钾氩等时线数据，使用的是钾氩激光实验（KArLE）的更新版本，该实验正在为未来行星物质的原位定年而开发。这些玄武岩的钾含量与月球克里普玄武岩或火星探测器发现的火成岩岩性相当，而之前的概念验证研究主要集中在钾含量更高的岩石上。我们旨在测量这些类似样本，以展示原位钾氩地质年代学不断提高的能力。
结合激光诱导击穿光谱（LIBS）、质谱（MS）和微观分析，我们测量了玄武岩样本上23个点的钾和氩含量。然后我们根据这些岩石构建了钾氩等时线图。实验用的实验平台仪器由与飞行设备等效的装置组成，包括一台30毫焦的钕钇铝石榴石激光和一台四极质谱仪。
尽管钾含量比之前的研究低得多，但对于年龄为3.807亿年和3.735亿年的岩石，等时线斜率分别得出380±44百万年和398±50百万年，这表明我们的仪器可实现优于25百万年（<7%）的精度。等时线截距均得出捕获氩约为1×10立方厘米标准温度和压力/克。
我们的实验结果表明，使用KArLE方法对行星表面普遍存在的玄武岩进行准确和精确的测量是可能的，这有助于解决行星科学中的一系列广泛问题。
