Fluid budgets along the northern Hikurangi subduction margin, New Zealand: the effect of a subducting seamount on fluid pressure

作者：Ellis Susan^*; Fagereng Ake; Barker Dan; Henrys Stuart; Saffer Demian; Wallace Laura; Williams Charles; Harris Rob

来源：Geophysical Journal International, 2015, 202(1): 277-297.

DOI：10.1093/gji/ggv127

• Fault zone rheology
• Rheology and friction of fault zones
• Subduction zone processes
• Continental margins: convergent
• High strain deformation zones
• New Zealand

We estimate fluid sources around a subducted seamount along the northern Hikurangi subduction margin of New Zealand, using thermomechanical numerical modelling informed by wedge structure and porosities from multichannel seismic data. Calculated fluid sources are input into an independent fluid-flow model to explore the key controls on overpressure generation to depths of 12 km. In the thermomechanical models, sediment transport through and beneath the wedge is calculated assuming a pressure-sensitive frictional rheology. The change in porosity, pressure and temperature with calculated rock advection is used to compute fluid release from compaction and dehydration. Our calculations yield more precise information about source locations in time and space than previous averaged estimates for the Hikurangi margin. The volume of fluid release in the wedge is smaller than previously estimated from margin-averaged calculations (similar to 14 m(3) yr(-1) m(-1)), and is exceeded by fluid release from underlying (subducting) sediment (similar to 16 m(3) yr(-1) m(-1)). Clay dehydration contributes only a small quantity of fluid by volume (similar to 2 m(3) yr(-1) m(-1) from subducted sediment), but the integrated effect is still significant landward of the seamount. Fluid source terms are used to estimate fluid pressures around a subducting seamount in the fluid-flow models, using subducted sediment permeability derived from porosity, and testing two end-members for decollement permeability. Models in which the decollement acts as a fluid conduit predict only moderate fluid overpressure in the wedge and subducting sediment. However, if the subduction interface becomes impermeable with depth, significant fluid overpressure develops in subducting sediment landward of the seamount. The location of predicted fluid overpressure and associated dehydration reactions is consistent with the idea that short duration, shallow, slow slip events (SSEs) landward of the seamount are caused by anomalous fluid pressures; alternatively, it may result from frictional effects of changing clay content along the subduction interface.

• 出版日期2015-7