Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater
Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater
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DOI：
10.1016/j.icarus.2018.10.023
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发表时间：
2019-03
期刊：
影响因子：
3.2
通讯作者：
F. Rivera‐Hernández;D. Sumner;N. Mangold;K. Stack;O. Forni;H. Newsom;A. Williams;M. Nachon;J. L'Haridon;O. Gasnault;R. Wiens;S. Maurice
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作者：
F. Rivera‐Hernández;D. Sumner;N. Mangold;K. Stack;O. Forni;H. Newsom;A. Williams;M. Nachon;J. L'Haridon;O. Gasnault;R. Wiens;S. Maurice
火星沉积岩中的粒度可以使用火星科学实验室（MSL）Curiosityrover上ChemCam仪器的激光诱导击穿光谱（LIBS）数据中的点对点化学变化来限制。由ChemCam激光器烧蚀的每个点的直径在中等至粗砂的尺寸范围内。因此，岩石的颗粒显着小于激光光斑尺寸产生散装岩石组成在每个LIBS点和低点到点化学变化LIBS点之间。相比之下，对颗粒大小与斑点大小相当或更大的岩石的分析包含了每个点上单个颗粒的贡献，并且通常具有很高的点对点化学变异性。基尼指数，一个统计参数，被用来计算点到点的化学变化的主要元素的氧化物组合物来自ChemCam LIBS数据。首先，在所有LIBS观察中，将每个LIBS主要元素氧化物组成的总范围从0归一化到1。然后计算每个LIBS观察中每种氧化物的基尼指数。最后，对每个氧化物的基尼指数取平均值，以得出每个LIBS观察的基尼指数平均得分GMEAN。GMEAN和粒度之间的相关性进行了验证，使用不同粒度的沉积岩从耶洛奈夫湾组和帕朗普山成员的穆雷形成在盖尔陨石坑。总的来说，细粒岩石的GMEAN小于粗粒岩石。为了将GMEAN校准到粒度，将基于高分辨率图像的视觉评估的粒度估计值与相同目标的GMEAN值进行比较，以创建校准尺度。这个校准的尺度被用来推断未知粒度的岩石的粒度。总体而言，预测的粒度未知的岩石与那些已知的粒度从相同的单位和/或基岩目标的粒度重叠。使用基于ChemCam LIBS数据的GMEAN推断的粒度与从图像中确定的粒度是互补的，这两种技术都可以用于改善Curiosity分析的岩石沉积环境的解释和未来的火星任务与LIBS，如火星2020漫游车。
Grain size in martian sedimentary rocks can be constrained using point-to-point chemical variabilities in Laser Induced Breakdown Spectroscopy (LIBS) data from the ChemCam instrument on the Mars Science Laboratory (MSL)Curiosityrover. The diameter of each point ablated by the ChemCam laser is in the range of medium to coarse sand in size. Thus, rocks with grains significantly smaller than the laser spot size produce bulk rock compositions at each LIBS point and low point-to-point chemical variability among LIBS points. In contrast, analyses of rocks with grains about the size of the spot or larger contain contributions from individual grains at each point and often have high point-to-point chemical variability. The Gini index, a statistical parameter, was used to calculate the point-to-point chemical variability in major-element oxide compositions derived from the ChemCam LIBS data. First, the total range of each LIBS major-element oxide composition was normalized from 0 to 1 across all LIBS observations. Then the Gini index was calculated for each oxide in each LIBS observation. Finally, the Gini indices of each oxide were averaged to derive a Gini index mean score, GMEAN, for each LIBS observation. A correlation between GMEANand grain size was validated using sedimentary rocks of various grain sizes from the Yellowknife Bay formation and the Pahrump Hills member of the Murray formation in Gale crater. Overall, finer-grained rocks had smaller GMEANthan coarser-grained rocks. To calibrate GMEANto grain size, grain size estimates based on visual assessment of high-resolution images were compared to GMEANvalues for the same targets to create a calibrated scale. This calibrated scale was used to infer the grain size of rocks with unknown grain size. Overall, the grain sizes predicted for rocks with unknown grain size overlapped with those of known grain size from the same units and/or bedrock targets. The grain sizes inferred using the GMEANbased on ChemCam LIBS data are complimentary to those determined from images and both techniques can be used to improve interpretations of the depositional environments of rocks analyzed byCuriosityand future Mars missions with LIBS, such as the Mars 2020 rover.