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Data report: clay mineral assemblages and illite/smectite diagenesis in cuttings from Hole C0002P, IODP Expedition 348, Nankai Trough accretionary prism1

Michael B. Underwood2


This report summarizes the results of X-ray diffraction analyses of cuttings samples (1–4 mm diameter) from Integrated Ocean Drilling Program Hole C0002P, which is located offshore southwest Japan. A total of 102 specimens (<2 µm size fraction) were analyzed from intermediate levels of the Nankai accretionary prism over a record-setting depth interval of 1975 to 3058 meters below seafloor (mbsf). Within lithologic Subunit Va, percentages of smectite in the bulk sediment average 18.0 wt% (standard deviation of 2.8), whereas values of illite and undifferentiated kaolinite + chlorite average 22.4 and 17.3 wt%, respectively (standard deviations of 3.2 and 1.8, respectively). Within lithologic Subunit Vb, percentages of smectite in the bulk sediment decrease to an average of 7.9 wt% (standard deviation of 3.4), whereas mean values of illite and kaolinite + chlorite increase to 28.4 and 22.8 wt%, respectively (standard deviations of 1.9 and 2.2, respectively). The expandability of illite/smectite mixed-layer clay within Subunit Va averages 62%, and values within Subunit Vb decrease downsection to a low of 40%. The proportion of illite in illite/smectite mixed-layer clays averages 39% within Subunit Va, and illitization within Subunit Vb increases steadily downsection to a mean of 59% illite. The illite crystallinity index shifts at approximately 2600 mbsf; values above are consistent with detrital sources that were exposed to epizone–anchizone metamorphic conditions, and values below match anchizone source conditions.

1 Underwood, M.B., 2017. Data report: clay mineral assemblages and illite/smectite diagenesis in cuttings from Hole C0002P, IODP Expedition 348, Nankai Trough accretionary prism. In Tobin, H., Hirose, T., Saffer, D., Toczko, S., Maeda, L., Kubo, Y., and the Expedition 348 Scientists, Proceedings of the Integrated Ocean Drilling Program, 348: College Station, TX (Integrated Ocean Drilling Program).

2 Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro NM 87801, USA.

Initial receipt: 10 May 2016
Acceptance: 18 November 2016
Publication: 10 March 2017
MS 348-204