Expedition 372A summary

Porosity and permeability evolution in the Tuaheni Landslide Complex at Hikurangi margin from IODP Sites U1517 and U1519

“…Such creeping would conduct to small-scale compressional and extensional features across the landslide, which have not been observed. On the contrary, the South TLC is marked by a transition from a compressive upper sediment-supplied mass to an extensive part near the toe where sediments are removed (Figure 2a) (Mountjoy et al, 2014;Barnes et al, 2019a). Later, Mountjoy et al (2013Mountjoy et al ( , 2014 observed that the upper limit of creeping occurs downslope of where a hydrate-related bottom-simulating-reflector (BSR) (and thus the base of gas hydrate stability (BGHS)) cutting through the landslide reaches the seafloor.…”

“…This zone also corresponds to the transition between compressional and extensional deformation of the South TLC. They suggested that gas hydrates may be involved in ongoing slow deformation and proposed three possible mechanisms: 1) gas hydrate dissociation at the BGHS; 2) a hydrate pressure valve model implying the repeated hydrofracturing and weakening of the gas hydrate zone with a transfer of the overpressure accumulated underneath low-permeability gas hydrate-bearing sediments to the landslide mass where the BGHS approaches the seafloor and 3) a hydrate glacier model with gas hydrate-bearing sediments showing creeping behaviour (Mountjoy et al, 2013Barnes et al, 2019a).…”

“…Two other sites were initially planned to be drilled in the compressive part of the landslide and a reference site outside the landslide mass (Pecher et al, 2014). Even if this second drilling phase was not achieved (Barnes et al, 2019a), the outcomes from Site U1517 (Barnes et al, 2019b) can be interpreted in light of the properties of the sedimentary section at Site U1519 (Barnes et al, 2019a). Site U1519 was drilled, logged and partially cored ~15 kilometres at the northeast of Site U1517, in the western part of the Tuaheni basin fed by the north component of the TLC (Figures 1b and 3) (Barnes et al, 2019c).…”

Data report: permeability and grain size of sediments, IODP Expeditions 372 and 375

“…International Ocean Discovery Program Expeditions 372 and 375 recovered cores from the Hikurangi Subduction Zone off the east coast of New Zealand (Barnes et al, 2019;Saffer et al, 2019) (Figure F1). In this study, we used flow-through permeability tests to measure the vertical permeability of 15 whole-round core samples.…”

“…Samples are from four sites. Site U1517 is located ~35 km from shore on the upper slope of the Hikurangi margin at a water depth of 720 m. Drilling at Site U1517 investi-gated the landslide mass and the gas hydrate stability zone of the Tuaheni Landslide Complex, and sediments consist primarily of clayey silt with sandy intervals (Barnes et al, 2019). Site U1518 is located ~73 km from shore on the lower continental slope near the trench, and sediments are composed of silty clay or mud alternating with thin beds of silt to silty sand.…”