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doi:10.2204/iodp.proc.314315316.202.2012 Data report: clay mineral assemblages from the Nankai Trough accretionary prism and the Kumano Basin, IODP Expeditions 315 and 316, NanTroSEIZE Stage 11Junhua Guo2 and Michael B. Underwood2AbstractThis report documents the composition of clay mineral assemblages from six sites along the Kumano transect of the Nankai Trough subduction zone offshore south-central Japan. Coring was completed during Expeditions 315 and 316 of the Integrated Ocean Drilling Program, as part of Stage 1 of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). A total of 702 samples of hemipelagic mud and mudstone were analyzed by X-ray diffraction, using oriented aggregates of the clay-size fraction (<2 µm). Smectite varies the most among the clay-size constituents, ranging in relative abundance from 6% to 66%. On average, the expandability of illite/smectite mixed-layer clay is equal to 65%, and there are no progressive changes in clay mineral diagenesis over the depths sampled. We recognize a temporal pattern in composition that is consistent with what has been documented elsewhere across the Nankai subduction margin. The detrital clays shifted gradually from a smectite-rich assemblage during the late Miocene to more illite-chlorite–rich assemblages during the Pliocene and Pleistocene. Most of the compositional differences between lithostratigraphic units can be attributed to differences in their depositional ages. |
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