- Chapter contents
- Abstract
- Introduction
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Methods - Results
- Acknowledgments
- References
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Figures
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Tables
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doi:10.2204/iodp.proc.348.204.2017
Data report: clay mineral assemblages and illite/smectite diagenesis in cuttings from Hole C0002P, IODP Expedition 348, Nankai Trough accretionary prism1
Michael B. Underwood2
Abstract
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.