scholarly journals Focused fluid seepage related to variations in accretionary wedge structure, Hikurangi margin, New Zealand

Geology ◽  
2019 ◽  
Vol 48 (1) ◽  
pp. 56-61 ◽  
Author(s):  
Sally J. Watson ◽  
Joshu J. Mountjoy ◽  
Philip M. Barnes ◽  
Gareth J. Crutchley ◽  
Geoffroy Lamarche ◽  
...  
Keyword(s):  
Fluid Flow ◽  
New Zealand ◽  
Fluid Pressure ◽  
Data Sets ◽  
Accretionary Wedge ◽  
Fault Mechanics ◽  
Spatial Coverage ◽  
Fluid Seepage ◽  
Pressure Regime ◽  
Subduction Setting

Abstract Hydrogeological processes influence the morphology, mechanical behavior, and evolution of subduction margins. Fluid supply, release, migration, and drainage control fluid pressure and collectively govern the stress state, which varies between accretionary and nonaccretionary systems. We compiled over a decade of published and unpublished acoustic data sets and seafloor observations to analyze the distribution of focused fluid expulsion along the Hikurangi margin, New Zealand. The spatial coverage and quality of our data are exceptional for subduction margins globally. We found that focused fluid seepage is widespread and varies south to north with changes in subduction setting, including: wedge morphology, convergence rate, seafloor roughness, and sediment thickness on the incoming Pacific plate. Overall, focused seepage manifests most commonly above the deforming backstop, is common on thrust ridges, and is largely absent from the frontal wedge despite ubiquitous hydrate occurrences. Focused seepage distribution may reflect spatial differences in shallow permeability architecture, while diffusive fluid flow and seepage at scales below detection limits are also likely. From the spatial coincidence of fluids with major thrust faults that disrupt gas hydrate stability, we surmise that focused seepage distribution may also reflect deeper drainage of the forearc, with implications for pore-pressure regime, fault mechanics, and critical wedge stability and morphology. Because a range of subduction styles is represented by 800 km of along-strike variability, our results may have implications for understanding subduction fluid flow and seepage globally.

Conjugate strike-slip faulting across a subduction front driven by incipient seamount subduction

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 493-498
Author(s):  
Sam R. Davidson ◽  
Philip M. Barnes ◽  
Jarg R. Pettinga ◽  
Andrew Nicol ◽  
Joshu J. Mountjoy ◽  
...  
Keyword(s):  
New Zealand ◽  
Seismic Reflection ◽  
Fluid Pressure ◽  
Strike Slip ◽  
Accretionary Wedge ◽  
Pore Fluid Pressure ◽  
Plate Convergence ◽  
Swath Bathymetry ◽  
Seamount Subduction ◽  
Overlying Strata

Abstract The initial stages of seamount subduction and associated deformation in an overriding accretionary wedge is rarely documented. Initial subduction of Bennett Knoll seamount and faulting of the overlying strata along the Hikurangi subduction margin, New Zealand, are here studied using multibeam swath bathymetry, subbottom profiles, and regional seismic reflection lines. Our results provide new insights into the earliest stages of seamount collision at sediment-rich margins. Differential shortening along the subduction front induced by seamount subduction is initially accommodated in the accretionary wedge by conjugate strike-slip faults that straddle the buried flanks of the seamount and offset the frontal thrusts by as much as 5 km. The geometries of the strike-slip faults are controlled by the seamount’s dimensions and aspect, the obliquity of plate convergence, pore-fluid pressure, and the thickness and rheology of the incoming sedimentary section. Strike-slip faults in such settings are ephemeral and overprinted by the formation of new structures as seamount subduction advances.

scholarly journals The contemporary force balance in a wide accretionary wedge: numerical models of the southcentral Hikurangi margin of New Zealand

2019 ◽  
Vol 219 (2) ◽  
pp. 776-795 ◽  
Author(s):  
Susan Ellis ◽  
Francesca Ghisetti ◽  
Philip M Barnes ◽  
Carolyn Boulton ◽  
Åke Fagereng ◽  
...  
Keyword(s):  
New Zealand ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Thick Layer ◽  
Force Balance ◽  
Physical Parameters ◽  
Accretionary Wedge ◽  
Plate Interface ◽  
Seismic Section

SUMMARY The southcentral Hikurangi subduction margin (North Island, New Zealand) has a wide, low-taper accretionary wedge that is frontally accreting a >3-km-thick layer of sediments, with deformation currently focused near the toe of the wedge. We use a geological model based on a depth-converted seismic section, together with physically realistic parameters for fluid pressure, and sediment and décollement friction based on laboratory experiments, to investigate the present-day force balance in the wedge. Numerical models are used to establish the range of physical parameters compatible with the present-day wedge geometry and mechanics. Our analysis shows that the accretionary wedge stability and taper angle require either high to moderate fluid pressure on the plate interface, and/or weak frictional strength along the décollement. The décollement beneath the outer wedge requires a relatively weaker effective strength than beneath the inner (consolidated) wedge. Increasing density and cohesion with depth make it easier to attain a stable taper within the inner wedge, while anything that weakens the wedge—such as high fluid pressures and weak faults—make it harder. Our results allow a near-hydrostatic wedge fluid pressure, sublithostatic fluid overpressure at the subduction interface, and friction coefficients compatible with measurements from laboratory experiments on weak clay minerals.

scholarly journals The coupling of dehydration and deformation results in localised fluid flow in the accretionary wedge – a novel study of calcite veins

2020 ◽  
Author(s):  
Ismay Vénice Akker ◽  
Christoph E. Schrank ◽  
Michael W.M. Jones ◽  
Cameron M. Kewish ◽  
Alfons Berger ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fluid Transport ◽  
Mechanical Stability ◽  
Fluid Pressure ◽  
Ductile Deformation ◽  
Accretionary Wedge ◽  
Seismic Zone ◽  
Calcite Veins ◽  
Deformation Features ◽  
Long Time

<p>In plate-convergent settings, fluid-saturated sediments dehydrate during subduction. The sediments are subsequently accreted to the upper plate. Along their dehydration-deformation path, the initial unconsolidated soft marine sediments become thick, foliated, impermeable meta-sedimentary sequences. Fluid flow through such ‘non’-porous low-permeability rocks is concentrated in fracture networks, ranging from the mm- to the km-scale. We study the interplay between ductile and brittle deformation processes and fluid flow by investigating calcite veins in slates from the exhumed European Alpine accretionary wedge across scales (µm to km). These slates experienced peak metamorphic temperatures between 200°C and 330°C and represent the transition between the upper aseismic and seismic zone. With the use of Synchrotron X-ray Fluorescence Microscopy (SXFM), we investigate the slates by visualizing trace-element distributions. This technique shows that alternating cycles of slow pressure-dissolution processes and brittle fracturing persist over long time scales. At the micron-scale, pressure solution of the initial carbonate-rich slates is indicated by an enrichment of newly recrystallized phyllosilicates on cleavage planes and in pressure shadows. These ductile deformation features are mutually overprinted by calcite veins (aperture 10 µm), which are nicely visualized with Sr-SXFM maps. Increasing compaction and recrystallization in the slate-rich matrix leads to progressed dehydration resulting in an increased pore fluid pressure and subsequent hydrofracturing. The micron-sized fractures are immediately filled in with minerals, which are oversaturated at that time in the fluid, resulting in the formation of (i) micron-veinlets. Micron-veinlets collect (ii) into mm-cm sized veins, which themselves form (iii) vein arrays and (iv) mega-arrays, respectively at the 50-100 m and 300-400 m scale. This upscaling of fluid pathways indicates a localised fluid transport through the accretionary wedge, which has important implications for the understanding of the mechanical stability of the accretionary wedge and related seismic activity.</p>

scholarly journals Fluid pressure evolution during the earthquake cycle controlled by fluid flow and pressure solution crack sealing

2002 ◽  
Vol 54 (11) ◽  
pp. 1139-1146 ◽  
Author(s):  
Jean-Pierre Gratier ◽  
Pascal Favreau ◽  
François Renard ◽  
Eric Pili
Keyword(s):  
Fluid Flow ◽  
Fluid Pressure ◽  
Pressure Solution ◽  
Earthquake Cycle ◽  
Crack Sealing ◽  
Pressure Evolution

scholarly journals The last 2 Myr of accretionary wedge construction in the central Hikurangi margin (North Island, New Zealand): Insights from structural modeling

2016 ◽  
Vol 17 (7) ◽  
pp. 2661-2686 ◽  
Author(s):  
Francesca C. Ghisetti ◽  
Philip M. Barnes ◽  
Susan Ellis ◽  
Andreia A. Plaza-Faverola ◽  
Daniel H. N. Barker
Keyword(s):  
New Zealand ◽  
Structural Modeling ◽  
Accretionary Wedge

Time Constraints on Seepage Through Fractured Regions on the Vestnesa Ridge off the W-Svalbard Coast

2021 ◽  
Author(s):  
Hariharan Ramachandran ◽  
Andreia Plaza-Faverola ◽  
Hugh Daigle ◽  
Stefan Buenz
Keyword(s):  
Fluid Flow ◽  
Effective Stress ◽  
Gas Hydrate ◽  
Fluid Pressure ◽  
Fracture Network ◽  
The Arctic ◽  
Stability Zone ◽  
Methane Seepage ◽  
Carbonate Formation ◽  
Hydrate Stability

<p>Evidences of subsurface fluid flow-driven fractures (from seismic interpretation) are quite common at Vestnesa Ridge (around 79ºN in the Arctic Ocean), W-Svalbard margin. Ultimately, the fractured systems have led to the formation of pockmarks on the seafloor. At present day, the eastern segment of the ridge has active pockmarks with continuous methane seep observations in sonar data. The pockmarks in the western segment are considered inactive or to seep at a rate that is harder to identify. The ridge is at ~1200m water depth with the base of the gas hydrate stability zone (GHSZ) at ~200m below the seafloor. Considerable free gas zone is present below the hydrates. Besides the obvious concern of amount and rates of historic methane seeping into the ocean biosphere and its associated effects, significant gaps exist in the ability to model the processes of flow of methane through this faulted and fractured region. Our aim is to highlight the interactions between physical flow, geomechanics and geological control processes that govern the rates and timing of methane seepage.</p><p>For this purpose, we performed numerical fluid flow simulations. We integrate fundamental mass and component conservation equations with a phase equilibrium approach accounting for hydrate phase boundary effects to simulate the transport of gas from the base of the GHSZ through rock matrix and interconnected fractures until the seafloor. The relation between effective stress and fluid pressure is considered and fractures are activated once the effective stress exceeds the tensile limit. We use field data (seismic, oedometer tests on calypso cores, pore fluid pressure and temperature) to constrain the range of validity of various flow and geomechanical parameters in the simulation (such as vertical stress, porosity, permeability, saturations).</p><p>Preliminary results indicate fluid overpressure greater than 1.5 MPa is required to initiate fractures at the base of the gas hydrate stability zone for the investigated system. Focused fluid flow occurs through the narrow fracture networks and the gas reaches the seafloor within 1 day. The surrounding regions near the fracture network exhibit slower seepage towards the seafloor, but over a wider area. Advective flux through the less fractured surrounding regions, reaches the seafloor within 15 years and a diffusive flux reaches within 1200 years. These times are controlled by the permeability of the sediments and are retarded further due to considerable hydrate/carbonate formation during vertical migration. Next course of action includes constraining the methane availability at the base of the GHSZ and estimating its impact on seepage behavior.</p>

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