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1. Data report: permeability, porosity, pore size, grain size, and microporosity of sediments from IODP Expedition 372/375 Sites U1517, U1518, and U1519

   https://doi.org/10.14379/iodp.proc.372B375.211.2024  

   Nole, M; Daigle, H (December 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   Constant rate-of-strain consolidation, nuclear magnetic resonance transverse relaxation time distribution, mercury injection capillary pressure, grain size distribution, and nitrogen adsorption microporosity measurements were performed on 13 whole-round core samples from International Ocean Discovery Program (IODP) Expedition 372/375 along the Hikurangi margin offshore New Zealand. In this report, whole-round core samples were analyzed from three different sites along the Hikurangi margin subduction zone: Sites U1517 and U1519 on the upper slope and Site U1518 near the Hikurangi Trench. All samples were composed of mostly silty clay to clayey silt sediments. Measurements were used to constrain in situ permeability, porosity, pore size distribution, and consolidation characteristics. Across seven samples from Site U1517, in situ permeability of clayey silts ranged 3.0 × 10−17 to 1.5 × 10−15 m2 and median pore sizes ranged 180–246 nm. A transition from overconsolidated to underconsolidated sediments as expressed by the overconsolidation ratio was identified between 50 and 73 meters below seafloor that aligned with the observed base of the Tuaheni Landslide Complex. Across samples at Site U1518, in situ permeability of silty clays ranged 3.7 × 10−16 to 5.5 × 10−15 m2 and median pore sizes ranged 140–320 nm. Across samples at Site U1519, permeability of silty clays ranged 6.4 × 10−16 to 6.0 × 10−14 m2 and median pore sizes ranged 187–300 nm. 

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2. Data report: clay mineral assemblages within biocalcareous and volcaniclastic inputs to the Hikurangi subduction zone, IODP Expedition 372B/375 Sites U1520 and U1526, offshore New Zealand

   https://doi.org/10.14379/iodp.proc.372B375.207.2021  

   Underwood, M.B. (October 2021, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   Inputs to the Hikurangi subduction zone, offshore North Island, New Zealand, include volcaniclastic conglomerates that were deposited during the Late Cretaceous on the flanks of the subducting basement of Hikurangi Plateau. The overlying succession of pelagic carbonates is early Paleocene to early Pleistocene in age and ranges in composition from calcareous mudstone to muddy chalk and chalk. A thick wedge of Quaternary trench sediments occupies the top of the stratigraphic succession. International Ocean Discovery Program Expedition 375 cored those subduction inputs at two sites. Site U1520 is located on the distal edge of the trench, and Site U1526 is located near the crest of Tūranganui Knoll, where a highly condensed section of pelagic-hemipelagic sediment covers the basalt basement. This report provides the results of 128 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent), where smectite + illite + undifferentiated (chlorite + kaolinite) + quartz = 100%. Clay minerals in the altered volcaniclastic conglomerates and basalt consist almost exclusively of smectite. At Site U1520, the normalized abundance of smectite in overlying biocalcareous sediments ranges from 28.3 to 72.9 wt% (mean = 54.2 wt%), whereas the abundance of illite ranges from 16.1 to 49.0 wt% (mean = 32.0 wt%). The range for undifferentiated chlorite + kaolinite is 0.3–17.8 wt% (mean = 7.4 wt%), and the range for clay-sized quartz is 2.7–20.5 wt% (mean = 6.4 wt%). Upsection depletion of smectite in those sediments is balanced by upsection enrichment of illite. That same age-dependent trend is evident in coeval biocalcareous drift sediments from Ocean Drilling Program Sites 1123 (North Chatham drift) and 1124 (Rekohu drift). Moving downsection at Site U1520, indicators of clay diagenesis are inconsistent. Values of illite crystallinity index increase (i.e., peak broadening), whereas the proportion of illite within illite/smectite mixed-layer clays increases with depth. 

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3. Data report: permeability, porosity, and frictional strength of core samples from IODP Expedition 366 in the Mariana forearc

   https://doi.org/10.14379/iodp.proc.366.202.2019  

   Morrow, C.A; Moore, D.E.; Lockner, D.A.; Bekins, B.A. (June 2019, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   Core samples from International Ocean Discovery Program (IODP) Expedition 366 were tested in the laboratory to determine permeability, porosity, density, and frictional strength and their relation to mineralogy as part of an effort to understand hydromechanical processes at convergent plate margins. Seven samples were tested from a depth range of 19.6 to 197.9 m below seafloor. The samples were derived from three serpentinite mud volcanoes in the Mariana forearc region that formed where slab-derived fluids and materials ascend along faults. The physical characteristics mirror compositional differences between predominantly serpentine-rich and saponite-rich samples. Permeability values ranged from 10−17 to 10−19 m2, low enough to facilitate the formation of high fluid pressures that have been observed in the Mariana and other subduction megathrust environments. Porosity ranged from 0.37 to 0.51 and density ranged from 1.66 to 2.01 g/cm3. Serpentine-rich samples have coefficients of friction of 0.2–0.4, consistent with crustal serpentinite from a variety of fault zones, whereas saponite-rich samples have friction values less than 0.2, consistent with saponite fault gouge from the San Andreas Fault Observatory at Depth (SAFOD) drill hole in California (USA). 

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4. Expedition 362 Scientific Prospectus Addendum: The Sumatra Subduction Zone

   https://doi.org/10.14379/iodp.sp.362add.2016  

   McNeill, L.; Dugan, B.; Petronotis, K. (July 2016, Scientific prospectus)

   null (Ed.)

   Due to the availability of new site survey data and previous changes that defined proposed Sites SUMA-11C and SUMA-12A as the primary sites for Expedition 362, two new proposed alternate sites have been selected: SUMA-23A and SUMA-24A. This addendum provides the scientific objectives for proposed Sites SUMA-23A and SUMA-24A, regional and detailed maps, and seismic profiles for the two sites. The site priorities and drilling and coring strategy remain unchanged from the original Expedition 362 Scientific Prospectus. The operations time estimates for all alternate sites are presented. The new proposed alternate Sites SUMA-23A and SUMA-24A are located above Fracture Zone 7B, which is located south of the current primary and alternate sites. The sites are located close to the epicenter of one of the 2012 Mw >8 earthquakes. These sites are still part of the input section to the southern 2004 earthquake rupture region of the subduction zone. Proposed Site SUMA-23A provides a section of Unit 1 (thin trench wedge) and a significant part of Unit 2 (Bengal-Nicobar submarine fan deposits and interbedded hemipelagite) overlying Fracture Zone 7B and includes sampling of 10 m of basement atop the basement high. Proposed Site SUMA-24A provides a section of Unit 1 (thin trench wedge) and a thinner part of Unit 2 (Bengal-Nicobar submarine fan deposits and interbedded hemipelagite) than proposed Site SUMA-23A, which overlies Fracture Zone 7B, and includes sampling of 10 m of basement atop the basement high. The new site survey data were acquired on board the Schmidt Ocean Institute (CA, USA) research vessel (R/V) Falkor in 2015 during the MegaTera experiment, an international project between the Earth Observatory Singapore (EOS), the Indonesian Institute of Sciences, Schmidt Ocean Institute (SOI), and Institut de Physique du Globe de Paris (France). SOI provided the R/V Falkor for the experiment, and EOS funded the rental of the seismic equipment. 

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5. Expedition 366 Preliminary Report: Mariana Convergent Margin and South Chamorro Seamount

   https://doi.org/10.14379/iodp.pr.366.2017  

   Fryer, P.; Wheat, G.; Williams, T. (November 2017, Preliminary report)

   null (Ed.)

   Geologic processes at convergent plate margins control geochemical cycling, seismicity, and deep biosphere activity in subduction zones and suprasubduction zone lithosphere. International Ocean Discovery Program (IODP) Expedition 366 was designed to address the nature of these processes in the shallow to intermediate depth of the Mariana subduction channel. Although no technology is available to permit direct sampling of the subduction channel of an intraoceanic convergent margin at depths up to 18 km, the Mariana forearc region (between the trench and the active volcanic arc) provides a means to access this zone. Active conduits, resulting from fractures in the forearc, are prompted by along- and across-strike extension that allows slab-derived fluids and materials to ascend to the seafloor along associated faults, resulting in the formation of serpentinite mud volcanoes. Serpentinite mud volcanoes of the Mariana forearc are the largest mud volcanoes on Earth. Their positions adjacent to or atop fault scarps on the forearc are likely related to the regional extension and vertical tectonic deformation in the forearc. Serpentinite mudflows at these volcanoes include serpentinized forearc mantle clasts, crustal and subducted Pacific plate materials, a matrix of serpentinite muds, and deep-sourced formation fluid. Mud volcanism on the Mariana forearc occurs within 100 km of the trench, representing a range of depths and temperatures to the downgoing plate and the subduction channel. These processes have likely been active for tens of millions of years at this site and for billions of years on Earth. At least 10 active serpentinite mud volcanoes have been located in the Mariana forearc. Two of these mud volcanoes are Conical and South Chamorro Seamounts, which are the furthest from the Mariana Trench at 86 and 78 km, respectively. Both seamounts were cored during Ocean Drilling Program (ODP) Legs 125 and 195, respectively. Data from these two seamounts represent deeper, warmer examples of the continuum of slab-derived materials as the Pacific plate subducts, providing a snapshot of how slab subduction affects fluid release, the composition of ascending fluids, mantle hydration, and the metamorphic paragenesis of subducted oceanic lithosphere. Data from the study of these two mud volcanoes constrain the pressure, temperature, and composition of fluids and materials within the subduction channel at depths of about 18 to 19 km. Understanding such processes is necessary for elucidating factors that control seismicity in convergent margins, tectonic and magma genesis processes in the forearc and volcanic arc, fluid and material fluxes, and the nature and variability of environmental conditions that impact subseafloor microbial communities. Expedition 366 centered on data collection from cores recovered from three serpentinite mud volcanoes that define a continuum of subduction-channel processes defined by the two previously cored serpentinite mud volcanoes and the trench. Three serpentinite mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoro) were chosen at distances 55 to 72 km from the Mariana Trench. Cores were recovered from active sites of eruption on their summit regions and on the flanks where ancient flows are overlain by more recent ones. Recovered materials show the effects of dynamic processes that are active at these sites, bringing a range of materials to the seafloor, including materials from the lithosphere of the Pacific plate and from subducted seamounts (including corals). Most of the recovered material consists of serpentinite mud containing lithic clasts, which are derived from the underlying forearc crust and mantle and the subducting Pacific plate. Cores from each of the three seamounts drilled during Expedition 366, as well as those from Legs 125 and 195, include material from the underlying Pacific plate. A thin cover of pelagic sediment was recovered at many Expedition 366 sites, and at Site U1498 we cored through serpentinite flows to the underlying pelagic sediment and volcanic ash deposits. Recovered serpentinites are largely uniform in major element composition, with serpentinized ultramafic rocks and serpentinite muds spanning a limited range in SiO2 , MgO, and Fe2 O3 compositions. However, variation in trace element composition reflects pore fluid composition, which differs as a function of the temperature and pressure of the underlying subduction channel. Dissolved gases H2 , CH4 , and C2 H6 are highest at the site furthest from the trench, which also has the most active fluid discharge of the Expedition 366 serpentinite mud volcanoes. These dissolved gases and their active discharge from depth likely support active microbial communities, which were the focus of in-depth subsampling and preservation for shore-based analytical and culturing procedures. The effects of fluid discharge were also registered in the porosity and GRA density data indicated by higher than expected values at some of the summit sites. These higher values are consistent with overpressured fluids that minimize compaction of serpentinite mud deposits. In contrast, flank sites have significantly greater decreases in porosity with depth, suggesting that processes in addition to compaction are required to achieve the observed data. Thermal measurements reveal higher heat flow values on the flanks (~31 mW/m2) than on the summits (~17 mW/m2) of the seamounts. The new 2G Enterprises superconducting rock magnetometer (liquid helium free) revealed relatively high values of both magnetization and bulk magnetic susceptibility of discrete samples related to ultramafic rocks, particularly in dunite. Magnetite, a product of serpentinization, and authigenic carbonates were observed in the mudflow matrix materials. In addition to coring operations, Expedition 366 focused on the deployment and remediation of borehole casings for future observatories and set the framework for in situ experimentation. Borehole work commenced at South Chamorro Seamount, where the original-style CORK was partially removed. Work then continued at each of the three summit sites following coring operations. Cased boreholes with at least three joints of screened casing were deployed, and a plug of cement was placed at the bottom of each hole. Water samples were collected from two of the three boreholes, revealing significant inputs of formation fluids. This suggests that each of the boreholes tapped a hydrologic zone, making these boreholes suitable for experimentation with the future deployment of a CORK-lite. An active education and outreach program connected with many classrooms on shore and with the general public through social media. 

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