Pickering, KT; (2014) Site C0002. In: Proceedings of the Integrated Ocean Drilling Program. (pp. 1-248). Integrated Ocean Drilling Program

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Abstract

Integrated Ocean Drilling Program (IODP) Site C0002 (proposed Site NT3-01B; Fig. F1) is the centerpiece of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project (Tobin and Kinoshita, 2006). Planned scientific and technical targets for IODP Expedition 338 included collecting logging-while-drilling (LWD), cuttings, and core data in the lower Kumano forearc basin and in the inner wedge of the Nankai accretionary complex and extending riser Hole C0002F to 3600 meters below seafloor (mbsf). This would extend the hole beyond the 20 inch casing point (860 mbsf), which was cemented in place during IODP Expedition 326 in 2010 (Expedition 326 Scientists, 2011) (Fig. F2). Riser drilling with the D/V Chikyu during Expedition 338 was to sample the interior of the accretionary complex in the midslope region beneath the Kumano forearc basin with both cores and drilling cuttings and to collect an extensive suite of LWD and mud-gas data to characterize the formation. Through the installation of two casing strings (16 inch casing from 860 to 2300 mbsf and 13⅜ inch casing from 2300 to 3600 mbsf), Expedition 338 was to prepare Hole C0002F for deeper drilling expected to reach the megasplay target during the 2014 and 2015 International Ocean Discovery Program riser drilling seasons. Because of weather and current conditions that caused the suspension of riser drilling operations (see below), LWD data and cuttings were only obtained from 860 to 2005 mbsf (Figs. F2, F3), and additional riserless coring (200–500, 900–940, and 1100–1120 mbsf) (Fig. F3) was completed at Site C0002 as part of contingency operations. The uppermost 1400 m section at Site C0002 was characterized with a comprehensive LWD program during IODP Expedition 314 (Hole C0002A) (Fig. F4) (Expedition 314 Scientists, 2009). The intervals 0–204 and 475–1057 mbsf were cored during IODP Expedition 315 (Holes C0002D and C0002B) (Expedition 315 Scientists, 2009b). The Kumano forearc basin sedimentary package extends from the seafloor to ~940 mbsf and is underlain by the deformed inner wedge of the accretionary package. The seismic reflection character of the entire zone from ~940 mbsf to the megasplay reflection at ~5200 mbsf exhibits virtually no coherent reflections that would indicate intact stratal packages, which is in contrast to the outer accretionary wedge seaward of the megasplay fault system (Fig. F2; also see Moore et al., 2009). This seismic character is thought to indicate complex deformation within the inner wedge of the Nankai accretionary prism.

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