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Abstract

International Ocean Discovery Program (IODP) Expedition 372 combines two research topics, slow slip events (SSEs) on subduction faults and actively deforming gas hydrate-bearing landslides (Proposal 841-APL). Our study area on the Hikurangi margin east of New Zealand provides unique locations for addressing both research topics.Gas hydrates have long been suspected of being involved in seafloor failure; not much evidence, however, has been found to date for gas hydrate-related submarine landslides. Solid, icelike gas hydrate in sediment pores is generally thought to increase seafloor strength, as confirmed by a number of laboratory measurements. Dissociation of gas hydrate to water and overpressured gas, on the other hand, may destabilize the seafloor, potentially causing submarine landslides.The Tuaheni Landslide Complex on the Hikurangi margin shows evidence for active, creeping deformation. Intriguingly, the landward edge of creeping coincides with the pinchout of the base of gas hydrate stability (BGHS) on the seafloor. We therefore hypothesize that gas hydrate may be linked to creeping by (1) repeated small-scale sliding at the BGHS, in a variation of the conventional model linking gas hydrates and seafloor failure; (2) overpressure at the BGHS due to a permeability reduction linked to gas hydrates, which may lead to hydrofracturing, weakening the seafloor and allowing transmission of pressure into the gas hydrate stability zone; or (3) icelike viscous deformation of gas hydrates in sediment pores, similar to onshore rock glaciers. The latter two processes imply that gas hydrate itself is involved in creeping, constituting a paradigm shift in relating gas hydrates to submarine slope failure. Alternatively, creeping may not be related to gas hydrates but instead be caused by repeated pressure pulses or linked to earthquake-related liquefaction. We have devised a coring and logging program to test our hypotheses.SSEs at subduction zones are an enigmatic form of creeping fault behavior. At the northern Hikurangi subduction margin (HSM), they are among the best-documented and shallowest on Earth. They recur about every 2 y and may extend close to the trench, where clastic and pelagic sediments about 1.0-1.5 km thick overlie the subducting, seamount-studded Hikurangi Plateau. The northern HSM thus provides an excellent setting to use IODP capabilities to discern the mechanisms behind slow slip fault behavior, as proposed in IODP Proposal 781A-Full.The objectives of Proposal 781A-Full will be implemented across two related IODP expeditions, 372 and 375. Expedition 372 will undertake logging while drilling (LWD) at three sites targeting the upper plate (midslope basin, proposed Site HSM-01A), the frontal thrust (proposed Site HSM-18A), and the subducting section in the trench (proposed Site HSM-05A). Expedition 375 will undertake coring at the same sites, as well as an additional seamount site on the subducting plate, and implement the borehole observatory objectives. The data from each expedition will be...

Data report: clay mineral assemblages within and beneath the Tuaheni Landslide Complex, IODP Expedition 372A Site U1517, offshore New Zealand

“…The coring program at Site U1517 (Figure F1B) was designed to groundtruth seismic reflection interpretations of an actively deforming landslide known as the Tuaheni Landslide Complex (TLC) (Barnes et al, 2017). The apparent submarine slide is thought to have initiated as a sudden failure, followed by slow, ongoing creep (Mountjoy et al, 2014;Barnes et al, 2017).…”

Forearc Basin Stratigraphy and Interactions With Accretionary Wedge Growth According to the Critical Taper Concept

“…Labels of C0002 and C0009 indicate Integrated Ocean Drilling Program-drilled sites (Expedition 315 Scientists, 2009;Expedition 319 Scientists, 2010). (d) Forearc basin in the northern Hikurangi margin (modified from Barnes et al, 2017). OAH = outer-arc high; MSF = megasplay fault.…”

Data report: standard mineral mixtures, normalization factors, and determination of error for quantitative X-ray diffraction analyses of bulk powders and clay-sized mineral assemblages

“…Quantitative XRD becomes more important when an expedition's science plan includes extensive whole-round sampling of cores for shore-based measurements of frictional, geotechnical, and hydrogeological properties; this emphasis is added because many such properties are modulated by bulk sediment composition. The science plans for International Ocean Discovery Program (IODP) Expeditions 372 and 375, which drilled in the Hikurangi subduction zone offshore New Zealand, fell into the second category (Barnes et al, 2017;Saffer et al, 2017). Accordingly, considerable effort was invested to generate reasonably accurate mineral abundance values using XRD data.…”