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doi:10.2204/iodp.proc.314315316.201.2011 Data report: refined method for calculating percentages of kaolinite and chlorite from X-ray diffraction data, with application to the Nankai margin of southwest Japan1Junhua Guo2 and Michael B. Underwood2AbstractCalculating accurate percentages of kaolinite and chlorite in marine sediments using X-ray diffraction (XRD) data is challenging because the minerals have similar d-values. Most approaches use a peak-intensity ratio or fitted-peak-area ratio and assume a linear fit between the ratio and the concentration of each mineral. To test this assumption, we mixed various proportions of kaolinite and chlorite standards and calculated each mineral’s individual peak area (PA) at ~3.5 Å along with the total area (TA) of the composite peak. A power function provides the best correlation coefficient for regression curves of the ratio of PA/TA versus the actual mineral concentration (weight percent). The average error using a doubled half-peak area approach is 2.6%. We tested the utility of the method by analyzing data from natural mudstone specimens from Ocean Drilling Program Sites 1177 and 1178 (central and western Nankai Trough). This documentation of temporal changes in concentrations of chlorite and kaolinite provides a basis for improved XRD analyses and interpretations of sediment provenance during the Integrated Ocean Drilling Program’s Nankai Trough Seismogenic Zone Experiment. |
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