Tectonic variations along the Hikurangi subduction margin, New Zealand, and relationships to fluid flow and cold seep sites
Lamarche, G.; Barnes, P. M. ; Bialas, J.; Henrys, S.; Pecher, I.; Netzeband, G.; Greinert, J. ; Mountjoy, J.; Pedley, K.; Crutchley, G. (2008). Tectonic variations along the Hikurangi subduction margin, New Zealand, and relationships to fluid flow and cold seep sites. Eos, Trans. (Wash. D.C.) 89(53): T23A-1996
In: Eos, Transactions, American Geophysical Union. American Geophysical Union: Washington. ISSN 0096-3941; e-ISSN 2324-9250
The structure and geomorphology of the Hikurangi subduction margin varies along strike primarily in response to changes in subducting crustal structure, convergence rate and obliquity, and sediment supply. New seismic reflection and multibeam bathymetric data are used to interpret the stratigraphy of the subducting sequence, the upper plate tectonic structures, and the geological framework for cold vent seep sites. The imbricated frontal wedge of the central margin is characteristic of wide (ca. 150 km), poorly drained and over pressured, low taper (~4°) accretionary thrust systems associated with a relatively smooth subducting plate, a thick trench-fill sedimentary sequence, weak basal decollement, and moderate convergence rate. This region differs from the northern, Hawkes Bay to East Cape, sector of the margin where subducting seamounts, faster convergence rate, and reduced trench sediment supply have resulted in a dramatically reduced and steeper active frontal wedge, complex deformation and uplift of frontal ridges above subducting asperities, and a tectonic regime dominated by non-accretion and tectonic erosion. Bottom simulating reflectors (BSRs) are widespread along the length of the margin. Five areas with multiple fluid/methane seep sites, referred to informally as Wairarapa, Uruti Ridge, Omakere Ridge, Rock Garden, and Builders Pencil, typically lie in about 700-1200 m water depth on the crests of thrust faulted ridges along the mid-slope. All of these seep sites lie near the outer edge of a deforming Cretaceous and Paleogene inner foundation, at the rear of the accreted trench fill turbidites. One seep site lies in close proximity to a major strike slip fault. Another occurs directly above a subducting seamount. Beneath the seafloor seeps on ridge crests there is typically a conspicuous break in the BSR, and commonly a seismically-resolvable fault-fracture network through which fluids and gas percolate. There is a clear relationship between the seep sites and major thrust faults, which are conduits for fluid and gas migration sourced from the deeper, inner parts of the thrust wedge, and probably from subducting sediments. We consider that the Cretaceous and Paleogene inner foundation is, on the whole, relatively impermeable and focuses fluid migration preferentially to its outer edge via major low angle thrust faults and the decollement.
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