10:00 AM - 10:15 AM
[MIS08-05] Preliminary results from IODP Exp. 372 Creeping Gas Hydrate Slides and Hikurangi LWD
Keywords:Gas hydrate, Creeping, Tuaheni Landslide Complex, Hikurangi Subduction Margin, Inorganic Geochemistry, Interstitial water
During the Exp.372 (conducted by R/V JOIDES Resolution, 26 November 2017 to 4 January 2018), we logged and cored from the seafloor to below the base of gas hydrate stability at one site (U1517) within the TLC. We also performed logging while drilling (LWD) into the upper plate, frontal thrust, and subduction section at three sites (U1518, U1519, U1520) in the Hikurangi trench to provide baseline logging data for IODP Exp.375.
Exp.375 will core these sites and an additional seamount site on the subducting plate, and will install borehole observatories.
At Site U1517, we recovered sediment with some pore-filling gas hydrate layers. Gas hydrate-bearing sediments were identified as cold spots using an infrared (IR) camera before core sectioning on the catwalk soon after core recovery because the dissociation of gas hydrate is endothermic reaction. After IR camera observation, whole-round cores were sub-sampled on the catwalk and samples were squeezed for onboard interstitial water analyses; titration for chlorinity and alkalinity, ion chromatography for anions and cations, spectrophotometry for silica, ammonium and phosphate and ICP-OES for major and minor elements. The dissociation of gas hydrate liberates freshwater and dilutes interstitial water thus chlorinity analysis is useful for estimating gas hydrate saturation in pore space. Gas hydrate saturation ranges between 2 and 68% at 130 to 170mbsf based on chlorinity analyses at U1517. Post-expedition analyses will provide additional data to gain further insight into the linkage between landslide complex and gas hydrates in the HSM.