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doi:10.2204/iodp.proc.338.206.2016 Data report: clay mineral assemblages in cuttings from Hole C0002F, IODP Expedition 338, upper Nankai Trough accretionary prism1Michael B. Underwood2 and Chen Song3AbstractThis report summarizes the results of X-ray diffraction analyses of cuttings samples (1–4 mm diameter) from Integrated Ocean Drilling Program Expedition 338 Hole C0002F, located offshore southwest Japan. We analyzed 37 specimens (<2 µm size fraction) from the upper Nankai accretionary prism, collected between 1190 and 1990 meters below seafloor. Smectite is generally the most abundant mineral in the clay-size fraction. Within lithologic Unit IV, smectite in the bulk sediment averages 25.1 wt% (standard deviation = 3.6), whereas illite and kaolinite + chlorite average 18.9 (standard deviation = 2.0) and 11.3 wt% (standard deviation = 2.3), respectively. Within Unit V, smectite in the bulk sediment decreases to an average of 21.8 wt% (standard deviation = 2.8) and values of illite and kaolinite + chlorite average 21.8 (standard deviation = 3.5) and 14.1 wt% (standard deviation = 3.5 and 2.4), respectively. The expandability of illite/smectite averages 69%, and values decrease downhole. The proportion of illite in illite/smectite mixed-layer clays averages 25%, and those values increase downhole. Values of illite crystallinity index (average = 0.52Δ°2θ) are consistent with detrital source areas exposed to advanced levels of diagenesis and anchizone metamorphism. |
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