[S-SS30_29PO1] New perspective of great earthquakes along subduction zones

[SSS30-P12] Preliminary results of lithology examined during IODP Expedition 348 in the accretionary wedge of the Nankai Trough

*Rina FUKUCHI¹, Anja SCHLEICHER², Ana MAIA³, Chen SONG⁴, Kiho YANG⁵, EXPEDITION 348, Scientists ⁶ (1.The University of Tokyo, 2.University of Michigan, 3.Cardiff University, 4.University of Missouri-Columbia, 5.Yonsei University, 6.IODP Expedition 348)

Keywords:IODP Expedition 338, NanTroSEIZE, Site C0002

International Ocean Discovery Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Expedition 348 took place from 13 September 2013 to 29 January 2014. This expedition was primarily designed to extend riser Hole C0002N to 3600 mbsf (in the event, C0002N sidetrack Hole C0002P was drilled to 3058.5 mbsf). We collected cuttings, core samples, mud gas, and logging data. Here we report the preliminary shipboard lithological results of IODP Expedition 348.Four lithologic units were identified at Site C0002 based on geological and geochemical characteristics of core and cuttings samples: Unit II (475-512.5 mbsf in Hole C0002M), Unit III (875.5-975.5 mbsf in Hole C0002N), Unit IV (975.5-1665.5 mbsf in Hole C0002N), and Unit V (1665.5-2325.5 mbsf in Hole C0002N, and 1965.5-3058.5 mbsf in Hole C0002P).Lithologic Unit II is dominated by fine-grained turbiditic deposits. Silty claystone is the main lithology, with subordinate fine-grained sandstone and sandy siltstone. Lithologic Unit III is dominated by silty claystone with trace amounts of very fine loose sand, containing common glauconite grains. Those units are interpreted to be the Kumano forearc basin sediments. Lithologic Unit IV is dominated by silty claystone, with sandstone as a minor lithology. Sandstone cuttings in this unit are generally very weakly consolidated, and occur as disaggregated loose sand. Lithologic Unit IV is divided into five subunits based on sand content and interpreted as the upper accretionary prism sediment. Lithologic Unit V is dominated by silty claystone. Fine-grained and moderately cemented sandstone was a minor component. In Hole C0002P, clay-size content in the silty claystone increases at the depth up to 2625.5 mbsf. The fine silty claystone becomes the dominant lithology from 2625.5 mbsf. This unit is possibly interpreted to be the trench or Shikoku Basin hemipelagic deposits.