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This dataset includes sediment pore water chemistry and porosity measurements from marine sediments offshore of the northern and southern Hikurangi margin, New Zealand. Samples were collected by the R/V Revelle on expedition RR1901/1902 (Principial investigator Evan Solomon; co-chief principal investigators Marta Torres and Robert Harris). Alongside heat flow measurements, push core, gravity core, and piston core samples were collected for porosity measurements and pore water extraction throughout seepage areas and diffuse flow settings spanning the shelf break to the deformation front. This study was designed to evaluate magnitude and distribution of heat flow, fluid flow, and chemical flux at the the investigated sites. This work is supported by NSF awards OCE-1753617, OCE-1753665.
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Geochemical and Thermal Constraints on the Hikurangi Subduction Zone Hydrogeologic System and Its Role in Slow Slip
Abstract Fluid generation and migration regulate the development of pore fluid pressure, which is hypothesized to influence the occurrence of slow slip events at subduction zones. Seafloor seep sites present the opportunity to directly sample fluids flowing through the accretionary wedge and assess the hydrogeologic conditions of the outer forearc. We present heat flow measurements and pore water geochemistry from sediment cores collected at fault‐hosted seep sites on the southern and northern Hikurangi margin, offshore the North Island of New Zealand. These measurements span the deformation front to the shelf break. Along the northern margin, heat flow data do not show anomalies that can be obviously attributed to the discharge of warm fluids. Pore fluid compositions indicate that seep fluids originate from compaction within the uppermost wedge. Reactive‐transport modeling of pore water solute profiles produces fluid flow rate estimates ≤2 cm/yr. Shallow fluid sources and low discharge rates at offshore fault‐hosted seeps suggest that the sampled fault zones are characterized by low permeability at depth, preventing efficient drainage of the megathrust and underthrust sediments to the seafloor. These results provide additional evidence that the northern Hikurangi margin plate boundary is associated with high pore fluid pressures that likely act as a control on slow slip activity.
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- Award ID(s):
- 1753617
- PAR ID:
- 10662096
- Publisher / Repository:
- Wiley Periodicals LLC
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 26
- Issue:
- 3
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Fluid flow and pore‐pressure cycling are believed to control slow slip events (SSEs), such as those that frequently occur at the northern Hikurangi margin of New Zealand. To better understand fluid flow in the forearc system we examined the relationship between several physical properties of Cretaceous‐to‐Pliocene sedimentary rocks from the Raukumara peninsula. We found that the permeability of the deep wedge is too low to drain fluids, but fracturing increases permeability by orders of magnitude, making fracturing key for fluid flow. In weeks to months, plastic deformation, swelling, and possibly not‐yet‐identified mechanisms heal the fractures, restoring the initial permeability. We conclude that overpressures at the northern HM might partly dissipate during SSEs due to enhanced permeability near faults. However, in the months following an SSE, healing in the prism will lower permeability, forcing pore pressure to rise and a new SSE to occur.more » « less
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null (Ed.)Slow slip events (SSEs) at the northern Hikurangi subduction margin, New Zealand, are among the best-documented shallow SSEs on Earth. International Ocean Discovery Program Expedition 375 was undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi Trough by (1) coring at four sites, including an active fault near the deformation front, the upper plate above the high-slip SSE source region, and the incoming sedimentary succession in the Hikurangi Trough and atop the Tūranganui Knoll Seamount, and (2) installing borehole observatories in an active thrust near the deformation front and in the upper plate overlying the slow slip source region. Logging-while-drilling (LWD) data for this project were acquired as part of Expedition 372 (26 November 2017–4 January 2018; see the Expedition 372 Preliminary Report for further details on the LWD acquisition program). Northern Hikurangi subduction margin SSEs recur every 1–2 years and thus provide an ideal opportunity to monitor deformation and associated changes in chemical and physical properties throughout the slow slip cycle. Sampling of material from the sedimentary section and oceanic basement of the subducting plate reveals the rock properties, composition, lithology, and structural character of material that is transported downdip into the SSE source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate all the way to the trench, indicating that the shallow thrust fault zone targeted during Expedition 375 may also lie in the SSE rupture area. Hence, sampling at this location provides insights into the composition, physical properties, and architecture of a shallow fault that may host slow slip. Expedition 375 (together with the Hikurangi subduction LWD component of Expedition 372) was designed to address three fundamental scientific objectives: (1) characterize the state and composition of the incoming plate and shallow plate boundary fault near the trench, which comprise the protolith and initial conditions for fault zone rock at greater depth and which may itself host shallow slow slip; (2) characterize material properties, thermal regime, and stress conditions in the upper plate above the core of the SSE source region; and (3) install observatories at an active thrust near the deformation front and in the upper plate above the SSE source to measure temporal variations in deformation, temperature, and fluid flow. The observatories will monitor volumetric strain (via pore pressure as a proxy) and the evolution of physical, hydrological, and chemical properties throughout the SSE cycle. Together, the coring, logging, and observatory data will test a suite of hypotheses about the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024GC011778
