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doi:10.2204/iodp.proc.348.203.2017 Data report: clay mineral assemblages in cuttings from Hole C0002N, IODP Expedition 348, Nankai Trough accretionary prism1Michael B. Underwood2AbstractThis report summarizes the results of X-ray diffraction analyses of cuttings samples (1–4 mm diameter) from Integrated Ocean Drilling Program Hole C0002N, which is located offshore southwest Japan. The analyses included 73 specimens (<2 µm size fraction) from the upper to middle levels of the Nankai accretionary prism. The cuttings were collected over a depth interval of 1175 to 2305 meters below seafloor (mbsf). Smectite is generally the most abundant clay mineral. Within lithologic Unit IV, percentages of smectite in the bulk sediment average 25.5 wt% (standard deviation = 5.7), whereas values for illite and undifferentiated kaolinite + chlorite average 19.5 and 11.9 wt%, respectively (standard deviations = 2.3 and 1.9). Within lithologic Unit V, percentages of smectite in the bulk sediment decrease to an average of 21.4 wt% (standard deviation = 2.1); mean values of illite and kaolinite + chlorite are 21.6 and 14.9 wt%, respectively (standard deviations = 2.1 and 2.5). The expandability of illite/smectite averages 64%, and values decrease downsection. The average proportion of illite in illite/smectite mixed-layer clays is 35%, and values increase downsection. The illite crystallinity index shifts at approximately 1495 mbsf; values above are consistent with detrital sources that were exposed to advanced diagenesis and anchizone metamorphic conditions; values below are smaller (higher apparent crystallinity) due to an analytical artifact. |
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