IODP Expedition 322 drills two sites to document inputs to the Nankai Trough subduction zone

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doi: 10.2204/iodp.sd.10.02.2010
Author(s): Underwood, Michael B.; Saito, Saneatsu; Kubo, Yu'suke
Integrated Ocean Drilling Program, Expedition 322 Scientists, College Station, TX
Author Affiliation(s): Primary:
University of Missouri, Department of Geological Sciences, Columbia, MO, United States
Other:
Japan Agency for Marine-Earth Science and Technology, Japan
Volume Title: Scientific Drilling
Source: Scientific Drilling, Vol.10, p.14-25. Publisher: Integrated Ocean Drilling Program Management International, Sapporo; Washington, DC, International. ISSN: 1816-8957
Note: In English. 40 refs.; illus., incl. sects., geol. sketch map
Summary: The primary goals during Expedition 322 of the Integrated Ocean Drilling Program were to sample and log the incoming sedimentary strata and uppermost igneous basement of the Shikoku Basin, seaward of the Nankai Trough (southwestern Japan). Characterization of these subduction inputs is one piece of the overall science plan for the Nankai Trough Seismogenic Zone Experiment. Before we can assess how various material properties evolve down the dip of the plate interface, and potentially change the fault's behavior from stable sliding to seismogenic slip, we must determine the initial pre-subduction conditions. Two sites were drilled seaward of the trench to demonstrate how facies character and sedimentation rates responded to bathymetric architecture. Site C0011 is located on the northwest flank of a prominent basement high (Kashinosaki Knoll), and Site C0012 is located near the crest of the seamount. Even though significant gaps remain in the coring record, and attempts to recover wireline logs at Site C0012 failed, correlations can be made between stratigraphic units at the two sites. Sedimentation rates slowed down throughout the condensed section above the basement high, but the seafloor relief was never high enough during the basin's evolution to prevent the accumulation of sandy turbidites near the crest of the seamount. We discovered a new stratigraphic unit, the middle Shikoku Basin facies, which is typified by late Miocene volcaniclastic turbidites. The sediment-basalt contact was recovered intact at Site C0012, giving a minimum basement age of 18.9 Ma. Samples of interstitial water show a familiar freshening trend with depth at Site C0011, but chlorinity values at Site C0012 increase above the values for seawater toward the basement contact. The geochemical trends at Site C0012 are probably a response to hydration reactions in the volcaniclastic sediment and diffusional exchange with seawater-like fluid in the upper igneous basement. These data are important because they finally establish an authentic geochemical reference site for Nankai Trough, unaffected by dehydration reactions, and they provide evidence for active fluid flow within the upper igneous crust. Having two sets of geochemical profiles also shows a lack of hydrogeological connectivity between the flank and the crest of the Kashinosaki Knoll.
Year of Publication: 2010
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; 20 Geophysics, Applied; Algae; Asia; Biostratigraphy; Boreholes; Cenozoic; Chronostratigraphy; Cores; Correlation; Crust; Drilling; Expedition 322; Far East; Geochemistry; Geophysical methods; Geophysical profiles; Geophysical surveys; Honshu; Hydrochemistry; IODP Site C0011; IODP Site C0012; Igneous rocks; Integrated Ocean Drilling Program; Japan; Kii Peninsula; Lithofacies; Lithostratigraphy; Magnetostratigraphy; Marine drilling; Marine sediments; Microfossils; Miocene; NanTroSEIZE; Nankai Trough; Nannofossils; Neogene; North Pacific; Northwest Pacific; Oceanic crust; Pacific Ocean; Physical properties; Plantae; Pore water; Sedimentary rocks; Sedimentation; Sedimentation rates; Sediments; Seismic methods; Seismic profiles; Seismic stratigraphy; Shikoku Basin; Subduction zones; Surveys; Tertiary; West Pacific
Coordinates: N324944 N324944 E1365254 E1365254
N324453 N324453 E1365501 E1365501
Record ID: 2011000998
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute.