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Site C00111

Expedition 322 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site C0011 (proposed Site NT1-07) was the primary site for IODP Expedition 322 (Saito et al., 2009). The site is located in the Shikoku Basin on the northwest flank of a prominent basement high (Kashinosaki Knoll) that was constructed on the subducting Philippine Sea plate (Fig. F1). The primary purpose of drilling at this location was to recover a complete section of sedimentary strata and uppermost igneous basement, thereby characterizing the subduction inputs to the Nankai Trough. Analysis of seismic reflection data just prior to drilling indicated a depth to basement of ~1050 meters below seafloor (mbsf). This estimate of total sediment thickness is considerably less than the value used in the Scientific Prospectus (1200 m thick). The adjustment was made after making refinements to the acoustic velocity model following successful acquisition of logging-while-drilling (LWD) data during the final days of IODP Expedition 319. The availability of LWD data was a major benefit for scientific productivity during Expedition 322 by guiding both operations and scientific interpretations. For example, the coring plan was modified to begin sampling at 340 m core depth below seafloor (CSF) rather than the original position of 400 m CSF, and plans to deploy the sediment temperature-pressure (SET-P) tool for in situ pressure measurements were adjusted to target the most favorable intervals on the logs.

By recovering a complete suite of cores and LWD logs from Site C0011, the Expedition 322 scientists expected to help answer the following questions:

  1. How does the physical hydrogeology of the Shikoku Basin respond to variations in primary lithologic architecture and basement structure?

  2. How do fluids in the igneous basement affect subduction processes?

  3. How have system-wide patterns of sediment dispersal affected composition within the Shikoku Basin, particularly on the northeast side of the fossil spreading ridge (Kinan seamount chain)?

  4. Which factor(s) inherited from the Shikoku Basin control(s) the décollement's position near the toe of the Nankai accretionary prism, as well as the location of ramps and flats and mechanical behavior throughout?

  5. Does the plate boundary fault, near its updip limit of seismicity, shift its position from a sediment/sediment interface (stable sliding) to the sediment/basalt interface (stick-slip)? If so, what are the causes?

Answers to these questions will require data from multiple drilling sites and expeditions and will contribute to the success of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) in many important ways. Fundamentally, the results from Expedition 322 will document initial conditions within presubduction equivalents of the seismogenic zone.

1Expedition 322 Scientists, 2010. Site C0011. In Saito, S., Underwood, M.B., Kubo, Y., and the Expedition 322 Scientists, Proc. IODP, 322: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.322.103.2010

2Expedition 322 Scientists' addresses.

Publication: 10 October 2010
MS 322-103