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Focussed fluid flow on the Hikurangi Margin, New Zealand – Evidence from possible local upwarping of the base of gas hydrate stability
Pecher, I.A.; Henrys, S. A. ; Wood, W. T. ; Kukowski, N.; Crutchley, G. J.; Fohrmann, M.; Kilner, J.; Senger, K. ; Gorman, A. R.; Coffin, R. B. ; Greinert , J.; Faure, K. (2010). Focussed fluid flow on the Hikurangi Margin, New Zealand – Evidence from possible local upwarping of the base of gas hydrate stability. Mar. Geol. 272(1-4): 99-113. dx.doi.org/10.1016/j.margeo.2009.10.006
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227, more
Peer reviewed article  

Available in  Authors 
    VLIZ: Open Repository 227431 [ OMA ]

Keyword
    Marine
Author keywords
    Fluid flow; Gas hydrates; Hikurangi Margin; Subduction zones

Authors  Top 
  • Pecher, I.A.
  • Henrys, S. A.
  • Wood, W. T.
  • Kukowski, N.
  • Crutchley, G. J.
  • Fohrmann, M.
  • Kilner, J.
  • Senger, K.
  • Gorman, A. R.
  • Coffin, R. B.
  • Greinert , J., more
  • Faure, K.

Abstract
    The southern Hikurangi Subduction Margin is characterized by significant accretion with predicted high rates of fluid expulsion. Bottom simulating reflections (BSRs) are widespread on this margin, predominantly occurring beneath thrust ridges. We present seismic data across the Porangahau Ridge on the outer accretionary wedge. The data show high-amplitude reflections above the regional BSR level. Based on polarity and reflection strength, we interpret these reflections as being caused by free gas. We propose that the presence of gas above the regional level of BSRs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids, although we cannot entirely rule out alternative processes. Simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low-permeability slope basins into the Porangahau Ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability. Focussing of fluid flow is predicted to take place deep in the accretionary wedge and/or the underthrust sediments. Above the high-amplitude reflections, sediment reflectivity is low. A lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas-hydrate-related amplitude blanking. Structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge. A gap in the BSR in the southern part of the study area may be caused by a loss of gas during fluid expulsion. We speculate that gaps in otherwise continuous BSRs that are observed beneath some thrusts on the Hikurangi Margin may be characteristic of other locations experiencing focussed fluid expulsion.

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