HR: 17:30h
AN: OS52D-07    [PDF]
TI: Southern Ritchie Banks, Hikurangi Margin, New Zealand - Similarities to Hydrate Ridge?
AU: Pecher, I A
EM: i.pecher@gns.cri.nz
AF: IGNS, PO Box 30-368, Lower Hutt, 6315 New Zealand
AU: * Henrys, S A
EM: s.henrys@gns.cri.nz
AF: IGNS, PO Box 30-368, Lower Hutt, 6315 New Zealand
AU: Zhu, H
EM: h.zhu@gns.cri.nz
AF: IGNS, PO Box 30-368, Lower Hutt, 6315 New Zealand
AB: The Hikurangi Margin offshore New Zealand's East Coast is predicted to contain large quantities of gas hydrates, based on the observation of wide-spread bottom simulating reflections (BSRs). The Hikurangi Plateau, a large igneous province populated by seamounts, is being subducted at this margin beneath the New Zealand continent. Subducting seamounts disrupt the margin and may underlie Ritchie Banks, a series of prominent outer-margin highs. We present results from three seismic lines across the Southern high of Ritchie Banks. BSRs are visible on the flanks of Southern Ritchie Banks clearly suggesting the presence of gas hydrates. At the crest, we were able to identify gas conduits that extend close to the seafloor. Depending on bottom water temperature, most of the crest is predicted to be within the methane hydrate stability zone. We therefore predict gas hydrates to be present above the gas conduits. One of the gas conduits is located beneath the projected location of a gas plume that has been identified previously in the water column, suggesting venting of gas through the gas hydrate stability zone. Southern Ritchie Banks displays similarities to Hydrate Ridge. Both ridges appear to be uplifted and form large-scale structures of fluid flow focusing. Water depths are similar and both ridges exhibit gas venting. Structural similarities include landward dipping layers at the seaward flanks of both ridges. We observe high seafloor reflectivity at the crest of Southern Ritchie Banks, perhaps indicative of carbonate cementation or even gas hydrate outcrops, similar to Hydrate Ridge. Our observations suggest that Southern Ritchie Banks may contain a very ``active'' gas hydrate system.
DE: 1615 Biogeochemical processes (4805)
DE: 1800 HYDROLOGY
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting