Fluid Budgets Along the Northern Hikurangi Subduction Margin, New Zealand: the Effect of a Subducting Seamount on Fluid Pressure
Abstract
The northern Hikurangi subduction margin, offshore North Island, New Zealand, has a shallow transition from locked to aseismically creeping behaviour (<5-15 km) that is accompanied by well-characterized slow-slip events. This region has recently been the focus of international efforts to understand transient slip events at subduction margins. Subduction of a seamount and excess pore fluid pressures along and above the subduction interface there have been implicated in the particularly shallow region over which slow-slip events have been observed We estimate fluid sources and sinks for the northern Hikurangi subduction margin using thermo-mechanical numerical modeling constrained by wedge structure and porosities from multichannel seismic data. Sediment transport through and beneath the accretionary wedge is calculated assuming a pressure-sensitive frictional rheology. The change in porosity, pressure and temperature with rock advection is used to compute fluid compaction and dehydration sources as sediment flows through and under the accretionary wedge. Computed fluid source terms yield more precise information about source locations in time and space than previous averaged estimates for the Hikurangi margin. The magnitude of fluid release in the accretionary wedge is an order of magnitude smaller than previously predicted for the entire margin, and is smaller than calculated fluid release from pore water in subducting sediments. Clay dehydration, while producing only small quantities of fluid, occurs over a large enough area to be a significant source landward of a subducted seamount imaged on the seismic profile. Fluid source terms are used to estimate fluid pressures around a subducting seamount. Models in which the decollement acts as a fluid conduit overlying low-permeability subducting sediment generate significant fluid overpressure landward of the seamount, supporting the idea that short duration, shallow, slow slip events in this region may be related to anomalous fluid pressures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.T43E2707E
- Keywords:
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- 8170 TECTONOPHYSICS Subduction zone processes;
- 8163 TECTONOPHYSICS Rheology and friction of fault zones;
- 8180 TECTONOPHYSICS Tomography;
- 5114 PHYSICAL PROPERTIES OF ROCKS Permeability and porosity