Submarine gas seepage in a mixed contractional and shear deformation regime: Cases from the Hikurangi oblique‐subduction margin

Abstract

[1] Gas seepage from marine sediments has implications for understanding feedbacks between the global carbon reservoir, seabed ecology, and climate change. Although the relationship between hydrates, gas chimneys, and seafloor seepage is well established, the nature of fluid sources and plumbing mechanisms controlling fluid escape into the hydrate zone and up to the seafloor remain one of the least understood components of fluid migration systems. In this study, we present the analysis of new three-dimensional high-resolution seismic data acquired to investigate fluid migration systems sustaining active seafloor seepage at Omakere Ridge, on the Hikurangi subduction margin, New Zealand. The analysis reveals at high resolution, complex overprinting fault structures (i.e., protothrusts, normal faults from flexural extension, and shallow (<1 km) arrays of oblique shear structures) implicated in fluid migration within the gas hydrate stability zone in an area of 2 3 7 km. In addition to fluid migration systems sustaining seafloor seepage on both sides of a central thrust fault, the data show seismic evidence for subseafloor gas-rich fluid accumulation associated with proto-thrusts and extensional faults. In these latter systems fluid pressure dissipation through time has been favored, hindering the development of gas chimneys. We discuss the elements of the distinct fluid migration systems and the influence that a complex partitioning of stress may have on the evolution of fluid flow systems in active subduction margins.

Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait

“…However, these features at the eastern Vestnesa segment are near vertical and dipping NE at >60° (Figure b), opposite dip to the emergent extensional faults north of KR [ Hustoft et al ., ].We suggest that these features are thus associated with shear deformation [e.g., Sylvester , ]. Similar scale faults have been recently documented in P‐Cable seismic data from the Hikurangi Margin, where seepage systems were suggested to be associated with Riedel shears [ Plaza‐Faverola et al ., ]. An interpretation of NW‐SE oriented shear‐related faults dissecting the Vestnesa Ridge with an extensional component supports the mixed simple and pure shear model proposed by Crane et al .…”

“…Episodic seepage at the updip termination of the GHSZ near the shelf break has been attributed to seasonal gas hydrate dissociation controlled by temperature variations [e.g., Berndt et al ., ; Phrampus and Hornbach , ; Skarke et al ., ; Westbrook et al ., ]. Longer‐term seepage periodicity (>10,000 years) has been attributed to pressure changes governed by processes associated with glacial‐interglacial cycles like sea level fluctuations, changes in sedimentation rates, and ice loading/unloading [e.g., Chand et al ., ; Davy et al ., ; Plaza‐Faverola et al ., ; Riboulot et al ., ] as well as fault reactivation mechanisms [e.g., Plaza‐Faverola et al ., ; Roberts and Carney , ; Zühlsdorff and Spiess , ]. Recent studies demonstrate the influence of inherited structural deformation, tectonic stresses, and fluid dynamics on modern margin evolution [ Autin et al ., ; Zoback et al ., ; Armitage et al ., ; Terakawa et al ., ].…”

Detection of Gas Hydrates in Faults Using Azimuthal Seismic Velocity Analysis, Vestnesa Ridge, W‐Svalbard Margin

“…The effect of faults on the distribution of gas hydrates is reported in different geological settings (Cooper & Hart, ; Dewangan et al, ; Lu et al, ; Madrussani et al, ; Minshull & White, ; Ruppel et al, ; Ruppel & Kinoshita, ). Northwestern Gulf of Mexico (Chen & Cathles, ; Cook et al, ; MacDonald et al, ; Milkov & Sassen, , ; Sassen et al, ; ), Black Ridge (Booth et al, ; Gorman et al, ; Paull et al, ; Rowe & Gettrust, ), Omakere Ridge (Plaza‐Faverola et al, ), Hydrate Ridge (Suess et al, , ; Tréhu et al, ; Tréhu, Flemings, et al, ; Weinberger & brown, ), Krishna‐Godavari Basin (Dewangan et al, ), and Qilian mountain permafrost (Lu et al, ) are examples of geological settings, where structural features play a big role in the distribution of gas hydrates. The effect of faults and fractures on the distribution of gas hydrates is even more pronounced on the fine‐grained sediments, where secondary porosity plays an important role in the formation of gas hydrates (Collett et al, ; Dewangan et al, ; Jaiswal et al, , ).…”

Splay fault branching from the Hikurangi subduction shear zone: Implications for slow slip and fluid flow

“…Fluid flow and seafloor seepage in continental margins have well established implications for the Earth's global climate [e.g., Etiope, 2009;MacDonald et al, 2002;Svensen et al, 2004], for prediction of hydrocarbon accumulations [Gay et al, 2003;Hovland et al, 2010], and for marine hazard assessment [Bugge et al, 1987;Judd and Hovland, 2007]. Although fluid expulsion from marine sediments to the seafloor is frequently manifested as pockmarks, mounds, mud volcanoes, or as direct seepage along faults [Barnes et al, 2010;Berndt, 2005;Judd and Hovland, 2007;Plaza-Faverola et al, 2014;Saffer and Bekins, 1999;Westbrook, 1991], tracking the origin of these fluids remains challenging but necessary for a full account of the fluid budget in continental margins.…”