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doi:10.2204/iodp.proc.338.207.2017 Data report: clay mineral assemblages in slope basin sediments and mass-transport deposits at Sites C0018 and C0021, IODP Expeditions 333 and 3381Michael B. Underwood2AbstractThis report summarizes the results of X-ray diffraction analyses of core samples from Sites C0018 and C0021 in the Nankai subduction zone (offshore southwest Japan). The Integrated Ocean Drilling Program recovered the cores during Expeditions 333 and 338, and a total of 122 specimens were analyzed (<2 mm size fraction). Depositional facies include trench slope deposits (hemipelagic mud with thin interbeds of turbidites and volcanic ash), mass-transport deposits (MTD), and sand-rich slope basin deposits. Illite is generally the most abundant clay mineral within both intact and MTD intervals. At Site C0018, the average amount of illite in the clay-size fraction of Subunit Ia (slope basin with MTD) is 37.7 wt% (standard deviation = 4.2). Proportions of smectite and chlorite average 26.8 and 20.2 wt%, respectively. Average contents of kaolinite and quartz are 4.1 and 11.3 wt%, respectively. Within Subunit Ib (sandy slope basin), the average contents are 37.2 wt% illite, 23.6 wt% smectite, 30.7 wt% undifferentiated chlorite + kaolinite, and 8.5 wt% quartz. Results are similar at Site C0021, where illite averages 43.7 wt% (standard deviation = 4.5). Average values for the other minerals are 23.6 wt% smectite, 24.3 wt% undifferentiated chlorite + kaolinite, and 8.4 wt% quartz. Most values of illite/smectite expandability fall between 55% and 65%. Values of the illite crystallinity index are indicative of detrital sources that were exposed to anchizone and epizone metamorphic conditions. |
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