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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Determining the modal mineralogy of mafic and ultramafic igneous rocks using thermal emission spectroscopy
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Determining the modal mineralogy of mafic and ultramafic igneous rocks using thermal emission spectroscopy

机译：用热发射光谱法测定镁铁质和超镁铁质火成岩的模态矿物学

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The modal mineralogies of 20 mafic and ultramafic igneous rocks were determined from their thermal infrared emission spectra using a linear deconvolution approach, which uses a library of end-member mineral spectra to model a bulk rock spectrum. Over 90% of the modes obtained from thermal emission spectra agree with modes obtained by traditional optical analyses to within the stated error of the optical analyses (5-15 vol %). Library spectra of several compositions within a solid solution series (e.g., plagioclase feldspars labradorite and bytownite) were commonly used in each best fit model and are assumed to represent, in combination, a composition in the rock for which an identical mineral spectrum was unavailable in the library. The accuracy of this assumption was evaluated by calculating a weighted average solid solution composition for plagioclase and/or pyroxenes from the library minerals used in the model best fit of 14 rocks and comparing these compositions to the actual chemistries measured by electron microprobe or the optically estimated An#. The derived solid solution compositions are generally within 10-15 An# (or Mg#) of the measured composition. Modal data derived from the spectra via the deconvolution were summed and converted to weight percent (wt %) oxides for comparison to standard bulk chemistry data. SiO2, Al2O3, and Na2O + K2O were generally slightly overestimated, and FeO and MgO were typically slightly underestimated. Modes and wt % oxides were plotted on standard rock type classification diagrams and provide broadly accurate classifications, demonstrating that the linear deconvolution technique is successful at deriving useful mineralogical information from thermal infrared emission spectra of bulk rock samples. Furthermore, convolution of the laboratory data to spectral resolutions comparable to remote sensing instruments (specifically, the Mars Global Surveyor Thermal Emission Spectrometer) demonstrates only a similar to 5 vol % increase in modal uncertainty for minerals present in abundances greater than or equal to 10 vol %. This study thus provides a strong foundation for the application of this technique to mafic igneous sample spectra from both laboratory and remote sensing instruments. [References: 29]
机译：使用线性反褶积方法，通过热解卷积方法，从20种镁铁质和超镁铁质火成岩的模态矿物学中确定了模型，该方法使用端成员矿物谱库对整体岩石谱进行建模。从热发射光谱获得的模态中超过90％与通过传统光学分析获得的模态在光学分析的规定误差内（5-15 vol％）相符。在每个最佳拟合模型中通常使用固溶体系列中几种成分的库谱（例如斜长石长石拉长石和bytownite），并假设它们共同代表了岩石中没有相同矿物谱的成分。图书馆。通过从14种岩石的模型最佳拟合中使用的库矿物中计算斜长石和/或辉石的加权平均固溶体成分并将这些成分与通过电子探针或光学估算的实际化学成分进行比较，来评估该假设的准确性一个＃。衍生的固溶体组成通常在所测组成的10-15 An＃（或Mg＃）以内。将通过反卷积从光谱中得出的模态数据求和，并转换为重量百分比（wt％）的氧化物，以便与标准批量化学数据进行比较。通常会稍微高估SiO2，Al2O3和Na2O + K2O，而通常会稍微低估FeO和MgO。模式和氧化物的重量百分比被绘制在标准岩石类型分类图上，并提供了广泛准确的分类，表明线性反褶积技术成功地从块状岩石样品的红外热发射光谱中得出了有用的矿物学信息。此外，将实验室数据卷积为可与遥感仪器（特别是火星全球测量员热发射光谱仪）相媲美的光谱分辨率表明，对于丰度大于或等于10 vol的矿物质，其模态不确定度仅增加了约5％vol％ ％。因此，这项研究为将该技术应用于实验室和遥感仪器的镁铁质火成样品光谱提供了坚实的基础。 [参考：29]

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