Expedition 322 summary

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 322 is part of the Nankai Trough Seismogenic Zone Experiment (NanTro-SEIZE) 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-logseismic data at Site C0011. The correlation of lithofacies and agedepth 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

Frictional properties of the shallow Nankai Trough accretionary sediments dependent on the content of clay minerals

“…This is also true in the Nankai Trough subduction zone, as revealed by the recent Integrated Ocean Drilling Program (IODP) Expeditions 316, 322, and 333 Underwood et al 2010;Expedition 333 Scientists 2012), part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). NanTroSEIZE IODP Expeditions 315, 316, 319, and 338 also revealed that the shallow (≤2,000 m below the seafloor) Nankai Trough accretionary prism is largely composed of claystone with subordinate siltstone, sandstone, and tuff Expedition 319 Scientists 2010;Strasser et al 2014).…”

“…Yellow arrows are convergence vectors between the Philippine Sea plate and Japan (Seno et al 1993;Heki 2007). The map in (a) is modified after Underwood et al (2010), while the seismic profile of (b) is provided by Y. Nakamura of the Japan Agency for Marine-Earth Science and Technology.…”

“…An accretionary prism is developed landward of the Nankai Trough (Figure 1). The Shikoku Basin sediments, composed of hemipelagic sediments and terrigenous turbidites, are actively accreting at the deformation front Underwood et al 2010; Figure 1b). An insequence thrust package of accreted sediments occupies the space between this deformation front and the outer ridge ( Figure 1b).…”

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“…We will use a combination of LWD at proposed Sites HSM-05 and HSM-18A, located in the Hikurangi Trough and frontal thrust, during Expedition 372 and coring during Expedition 375. These activities will be followed by a strategy of carefully coordinated sampling and postexpedition laboratory analyses (e.g., Screaton et al, 2009;Underwood et al, 2010). Proposed Site HSM-05A will target the entire sediment package on top of the Hikurangi Plateau.…”

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“…This hole was suspended with a temporary observatory attached to a retrievable bridge plug (termed the "SmartPlug") to monitor temperature and pore pressure at the fault zone. Expedition 322 characterized the subduction inputs at Integrated Ocean Drilling Program Sites C0011 and C0012 (Underwood et al, 2010). Two more Stage 2 expeditions followed a year later.…”