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      Expedition 322 summary

      , , , Expedition 322 Scientists
      Proceedings of the IODP
      Integrated Ocean Drilling Program

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          Abstract

          Integrated Ocean Drilling Program (IODP) Expedition 322 is part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and was designed to document characteristics of incoming sedimentary strata and upper igneous basement prior to their arrival at the subduction front. To accomplish these objectives, coring was conducted at two sites in the Shikoku Basin on the subducting Philippine Sea plate. Site C0011 is located on the northwest flank of a prominent bathymetric high (the Kashinosaki Knoll), whereas Site C0012 is located near the crest of the knoll. The resulting data, which include logging while drilling during IODP Expedition 319, provide a wealth of new information on presubduction equivalents of the seismogenic zone. Unfortunately, coring at Site C0011 began at 340 m core depth below seafloor (CSF) and failed to reach the total depth target because of premature destruction of the drill bit at 876 m CSF. Coring at Site C0012, however, penetrated almost 38 m into igneous basement and recovered the sediment/basalt interface intact at 537.81 m CSF. The age of basal sediment (reddish brown pelagic claystone) is >18.9 Ma. This recovery of basement was a major achievement, as was the comprehensive integration of core-log-seismic data at Site C0011. The correlation of lithofacies and age-depth models from the two sites within the Shikoku Basin shows changes from an expanded section (Site C0011) to a condensed section (Site C0012) and captures all of the important ingredients of basin evolution, including a previously unrecognized interval of late Miocene tuffaceous and volcaniclastic sandstone designated the middle Shikoku Basin facies. An older (early to middle Miocene) turbidite sandstone/siltstone facies with mixed detrital provenance occurs in the lower Shikoku Basin; this unit may be broadly correlative with superficially similar Miocene turbidites on the western side of the basin. When viewed together, the two sites around the Kashinosaki Knoll not only demonstrate how basement relief influenced rates of hemipelagic and turbidite sedimentation in the Shikoku Basin, but also build the complete lithostratigraphic template on which all of the postexpedition laboratory results can be placed. Those forthcoming details will include mineral and volcanic ash composition, geotechnical properties, frictional properties, and hydrological properties. Another triumph came from geochemical analyses of interstitial water and hydrocarbons at Site C0012. Unlike other so-called reference sites in the Nankai Trough, interstitial water on top of the basement high is largely unchanged by the effects of focused bedding-parallel flow and/or in situ reactions associated with rapid burial beneath the trench wedge and frontal accretionary prism. Thus, Site C0012 finally provides a reliable geochemical reference site for the subduction zone. In addition, geochemical evidence points to the presence of a seawater-like fluid within the upper basaltic crust, which is actively exchanging with the ocean and altering the interstitial water composition of the deep sediments by diffusional exchange.

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          Most cited references52

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          A model for the motion of the Philippine Sea Plate consistent with NUVEL-1 and geological data

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            Source mechanisms and tectonic significance of historical earthquakes along the nankai trough, Japan

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              Splay Fault Branching Along the Nankai Subduction Zone

              J.-O. Park (2002)
              Seismic reflection profiles reveal steeply landward-dipping splay faults in the rupture area of the magnitude (M) 8.1 Tonankai earthquake in the Nankai subduction zone. These splay faults branch upward from the plate-boundary interface (that is, the subduction zone) at a depth of approximately 10 kilometers, approximately 50 to 55 kilometers landward of the trough axis, breaking through the upper crustal plate. Slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion.

                Author and article information

                Journal
                10.2204/iodp.proc.322.2010
                Proceedings of the IODP
                Integrated Ocean Drilling Program
                1930-1014
                10 October 2010
                Article
                10.2204/iodp.proc.322.101.2010
                ee4e06d6-8510-44eb-939a-848d0cff6f0b

                This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History

                Earth & Environmental sciences,Oceanography & Hydrology,Geophysics,Chemistry,Geosciences

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