The habitat of slow slip phenomena in the Hikurangi subduction zone

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Subduction zones - where an oceanic plate is subducting beneath a continental plate – are among the most geologically dynamic systems on earth. In the last decade our knowledge of fault slip behavior in this realm has tremendously increased in response to advances in seismological and geodetic instruments. The newly discovered fault slip modes can last for months and thus are termed slow earthquakes. The geological factors that control such slip behavior is still subject to debate. Expedition 375 has been scheduled from March 8th, 2018, to May 5th, 2018, for R/V JOIDES Resolution to sample and log the frontal thrust, upper plate and incoming sediment plus oceanic crust in order to characterize the habitat that hosts shallow slow slip earthquakes in the northern Hikurangi subduction margin offshore New Zealand. Drill sites at the frontal thrust and on the upper plate target fault zones where fluid migration to the seafloor is expected, which will provide a window to the slow slip source region. The proposed research aims at the identification and spatio-temporal characterization of important diagenetic processes and their influence on the hydro-mechanical state of the subduction thrust through diagenesis, clay dehydration processes and fluid migration. The research will be implemented by a coordinated strategy of fluid and whole rock geochemistry in combination with boron and lithium isotope analysis to identify water-rock interaction processes, hydrothermal compaction tests to determine the temperature-dependence of the geochemical fingerprints from the identified processes and integration of the geochemical data with reaction-transport models to constrain the spatio-temporal occurrence of water-rock interaction and fluid migration in the subduction zone forearc.