IODP Expedition 333: Return to Nankai Trough Subduction Inputs Sites and Coring of Mass Transport Deposits

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 333 returned to two sites drilled during IODP Expedition 322 on the ocean side of the Nankai Trough to pursue the characterization of the inputs to the Nankai subduction and seismogenic zone, as part of the Nankai Trough Seismogenic Experiment (NanTroSEIZE) multi-expedition project. Site C0011 is located at the seaward edge of the trench and Site C0012 on a basement high, Kashinozaki Knoll (Fig. 1). The main objectives of drilling again at these sites were to fill coring gaps in the upper part (<350 m) of the sedimentary sequence, to measure heat flow, and to core the oceanic basement to a greater depth on the Knoll. New results include the observation of a diagenetic boundary within the Shikoku Basin sediments that may be compared to one documented further west by ODP Legs 131, 190 and 196 but occurs here at a lower temperature. Borehole heat flow measurements confirm spatial variations in the Shikoku Basin that were indicated by short probe surveys. Heat flow variations between topographic highs and lows may be related to fluid convection within the basement. This expedition also included the objectives of the Nankai Trough Submarine LandSLIDE history (NanTroSLIDE) Ancillary Project Letter (APL) and cored at Site C0018 a pile of mass transport deposits on the footwall of the megasplay fault, a major out of sequence thrust that presumably slips coseismically during large subduction earthquakes. This brought new insight on the timing of these mass wasting events and on the deformation within the sliding slope sediments. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.14.01.2012" target="_blank">10.2204/iodp.sd.14.01.2012</a>

Possible climate preconditioning on submarine landslides along a convergent margin, Nankai Trough (NE Pacific)

“…There is possibly sediment input from the NNE, from the Tenyu or Fuji rivers (Usman et al 2014), but as the sediments deposited in the studied basin are very fine grained, this represents only the very distal to pelagic part of the supplied sediment. The sedimentation rates at C0018A determined in this study vary by~100 cm/kyr (which is the same order of magnitude as estimated by Henry et al 2012). A significant increase in sedimentation rate is only observed before MTDs 3 and 4 of up to 300 cm/kyr.…”

“…3) and is composed of bioturbated hemipelagic mud with subhorizontal and SE-dipping volcanic ash layers that are a few centimeters thick, and is intercalated with a succession of six MTDs (MTD 1 to MTD 6; Fig. 3; Henry et al 2012;Strasser et al 2012). The MTDs are recognized based on their chaotic pebbly and/or mixed lithologies with inclined layers and shear zones Strasser et al 2012).…”

“…The studied sediment sequence was retrieved from a slope basin located~3 km seaward of the outer forearc high, which constitutes a natural boundary between the Kumano forearc basin and the outer Nankai accretionary prism ( Fig. 1; Henry et al 2012;Strasser et al 2011).…”

Shear strength of sediments approaching subduction in the Nankai Trough, Japan as constraints on forearc mechanics

“…[8] Although recovery of the sedimentary section from Site C0011 over the course of Expeditions 322 and 333 was incomplete, lithostratigraphic units were successfully correlated with C0012 [Henry et al, 2012a]. The major lithologies of Sites C0011 and C0012 are hemipelagic deposits with volcanic ash (Unit I), alternating silty claystone and volcaniclastic tuffaceous sandstone (Unit II), hemipelagic deposits lacking in ash (Unit III), a turbidite facies (Unit IV), and a volcaniclastic unit (Unit V); all are Miocene age or younger.…”

Flow dynamics of Nankai Trough submarine landslide inferred from internal deformation using magnetic fabric

“…(c) Schematic lithology of Hole C00018A, showing main lithostratigraphic units and interpreted facies, as well as relative depths of drilled intervals with mass‐transport deposits. Ages are derived from nannofossil event data, paleomagnetic stratigraphy, and tephra stratigraphy (modified from Expedition 333 Scientists, ).…”