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doi:10.2204/iodp.proc.333.104.2012

Site C0011¹

Expedition 333 Scientists²

Background and objectives

Integrated Ocean Drilling Program (IODP) Expeditions 322 and 333 were designed to document characteristics of incoming sedimentary strata and uppermost igneous basement prior to their arrival at the subduction front (Saito, Underwood, Kubo, and the Expedition 322 Scientists, 2010). To accomplish those objectives, coring was conducted at two sites on the subducting Philippine Sea plate. IODP Site C0011 is located on the northwest flank of a prominent bathymetric high (the Kashinosaki Knoll) (Ike et al., 2008), whereas IODP Site C0012 is located near the crest of the knoll (Fig. F1). Data acquired during Expedition 322 and logging-while-drilling (LWD) data at Site C0011 acquired during IODP Expedition 319 provide information on presubduction equivalents of the seismogenic zone (Underwood et al., 2010). Core samples at Site C0011 were obtained by rotary core barrel (RCB) drilling from 340 to 876 meters below seafloor (mbsf), where the hole was abandoned because of drill bit failure. Merging lithofacies and age-depth models shows how correlative units change from an expanded section at Site C0011 to a condensed section at Site C0012 (Fig. F2). Geochemical analyses of interstitial water at Site C0011, where chlorinity decreases with depth, suggested an effect of focused flow and/or in situ dehydration reactions associated with rapid burial beneath the trench wedge and frontal accretionary prism. By contrast, Site C0012 displayed increasing chlorinity with depth and evidence of upward diffusion of sulfate and other dissolved chemical species from the basement (Underwood et al., 2010). Site C0012 is thought to represent a geochemical reference site unaffected by subduction processes.

The specific questions addressed by additional drilling at Site C0011 are

• Is fluid circulation in basement and permeable sedimentary layers influencing heat flow and diagenesis at Sites C0011 and C0012?

• How does contrasting interstitial fluid chemistry at Sites C0011 and C0012 relate with in situ diagenesis and fluid flow?

• Can a change of physical properties between 200 and 250 mbsf at Site C0011 be related to lithologic variation or silica diagenesis?

The main objectives for returning to Site C0011 were to perform temperature measurements for heat flow determination and expand the age-depth models into the Pliocene and Quaternary. This was necessary because the upper stratigraphic intervals of the Shikoku Basin were not adequately sampled during Expedition 322. Additional coring provided complete profiles of organic and interstitial water geochemistry and sampled across prominent discontinuities in physical properties identified from LWD data (Saito, Underwood, Kubo, and the Expedition 322 Scientists, 2010).

¹ Expedition 333 Scientists, 2012. Site C0011. In Henry, P., Kanamatsu, T., Moe, K., and the Expedition 333 Scientists, Proc. IODP, 333: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.333.104.2012

² Expedition 333 Scientists’ addresses.

Publication: 18 May 2012
MS 333-104

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