Résumé
Holes C0002Q-C0002T were drilled in the inner accretionary prism of the Nankai Trough during International Ocean Discovery Program (IODP) Expedition 358. Sample depths range 2827.5-3067.5 meters below seafloor (mbsf). This report provides the results of X-ray diffraction analyses of the clay-sized fraction (<2 mu m spherical settling equivalent) from 33 specimens of bulk cuttings (1-4 mm size fraction). Four core samples from Hole C0002T were also analyzed. Mean weight percent values for common clay-sized minerals are smectite = 20.0 wt%, illite = 54.5 wt%, undifferentiated (chlorite + kaolinite) = 13.8 wt%, and quartz = 11.7 wt%. The average value of the illite crystallinity index is 0.64Delta degrees 2theta . Values of expandability for smectite + illite/smectite (I/S) mixed-layer clay average 57%, and the average proportion of illite in I/S clay is 46%. Depth-dependent trends are not evident in either the clay mineral assemblages or diagenetic indicators. Significant discrepancies exist between these new results and data from the overlapping depth intervals in Hole C0002P. A total of 18 core samples from IODP Hole C0025A in the central Kumano Basin were also analyzed, covering a depth range of 406.12-571.94 mbsf. In Lithologic Unit I (lower fore-arc basin facies), the mean values are smectite = 16.5 wt%, illite = 58.4 wt%, undifferentiated (chlorite + kaolinite) = 14.8 wt%, and quartz = 10.4 wt%. The statistics are similar for Lithologic Unit II (trench-slope facies): smectite = 23.7 wt%, illite = 54.1 wt%, undifferentiated (chlorite + kaolinite) = 11.9 wt%, and quartz = 10.3 wt%. The average value of the illite crystallinity index is 0.55Delta degrees 2theta . The expandability of smectite + I/S averages 60%, and the average proportion of illite in I/S is 20%.