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Contrasted porosity between the hanging-wall and the footwall of the active Pāpaku thrust at IODP Site U1518: insights on deformation and erosion history and sediment compaction state evolution during accretion at the northern Hikurangi margin deformation front
  • Jade Dutilleul,
  • Sylvain Bourlange,
  • yves géraud
Jade Dutilleul
Université de Lorraine, CNRS, GeoRessources

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Sylvain Bourlange
Université de Lorraine
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yves géraud
Université de Lorraine, CNRS, GeoRessources
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Attempts to determine physical property across thrust faults at subduction zones through drilling, logging and core sampling have been limited and restricted to exhumed accretionary prisms or shallow parts of active wedges. However, characterizing porosity evolution across the sedimentary section entering subduction zones and accreted sediments is crucial to understand deformation history at accretionary margins through determination of sediment trajectories, quantification of transported volumes of sediments and fluids with related mechanical responses and understanding deformation processes in and around fault zones. International Ocean Discovery Program Expeditions 372 and 375 drilled, logged and cored the entering basin (Site U1520) and active Pāpaku thrust (Site U1518) few kilometers landward of the northern Hikurangi margin deformation front where tsunami earthquakes and recurrent slow slip events occur. Here, we examine physical properties evolution across the Pāpaku thrust at Site U1518 including geophysical logging data, pore size distribution obtained by combining Nuclear Magnetic Resonance and Mercury Injection Capillary Pressure, and interstitial porosity that is representative of sediment compaction state, and compare with that of Site U1520. Interstitial porosity is determined by correcting total connected porosity from clay-bound water content based on cation exchange capacity. We evidence strong variations of physical properties across the thrust fault, with lower porosity, higher P-wave velocity and resistivity in the hanging-wall than in the footwall. We suggest that the porosity pattern at the Pāpaku thrust evidences differences in maximum burial depth with an overcompacted hanging-wall that has been uplifted, thrusted and concomitantly eroded above a nearly normally consolidated younger footwall.
Oct 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 10. 10.1029/2020GC009325