HR: 08:15h
AN: T41D-02    [Abstracts]
TI: Electrical resistivity structure of a transitional ocean-continent subduction zone: the Marlborough strike-slip system, northern South Island, New Zealand
AU: * Wannamaker, P E
EM: pewanna@egi.utah.edu
AF: University of Utah, Energy & Geoscience Institute 423 Wakara Way, Ste 300, Salt Lake City, UT 84108, United States
AU: Caldwell, G
EM: g.caldwell@gns.cri.nz
AF: GNS Science, P.O. Box 30368 Lower Hutt, Wellington, 6315, New Zealand
AU: Hill, G J
EM: gjhill77@gmail.com
AF: Monash University, Wellington Road, Clayton, VIC 3800, Australia
AU: Jiracek, G R
EM: jiracek@moho.sdsu.edu
AF: San Diego State University, Dept. of Geological Sciences 5500 Campanile Drive, San Diego, CA 92182, United States
AU: Bibby, H M
EM: h.bibby@gns.cri.nz
AF: GNS Science, P.O. Box 30368 Lower Hutt, Wellington, 6315, New Zealand
AU: Heise, W
EM: w.heise@gns.cri.nz
AF: GNS Science, P.O. Box 30368 Lower Hutt, Wellington, 6315, New Zealand
AU: Maris, V
EM: vmaris@egi.utah.edu
AF: University of Utah, Energy & Geoscience Institute 423 Wakara Way, Ste 300, Salt Lake City, UT 84108, United States
AU: Bennie, S
EM: s.bennie@gns.cri.nz
AF: GNS Science, P.O. Box 30368 Lower Hutt, Wellington, 6315, New Zealand
AB: The Marlborough strike slip fault system of the northern South Island, New Zealand, lies in the transition of plate convergence from near decoupling between upper and lower plates in true subduction (northern North Island), to essentially complete coupling between the plates with near-continuous lithospheric thickening and no subduction (central South Island). Here, four major dextral fault zones at a low angle to the present Australian- Pacific plate convergence direction accommodate most of the component of motion parallel to the plate boundary, while Pacific plate underthrusting and modest uplift take up most of the boundary-normal plate motion. Study of the Marlborough system may clarify controls on internal physical state of strike slip fault zones because of the differing degrees and rates of fault slip in a crust of unusually uniform composition. It should also fill a gap in understanding of transpressional orogens between uncoupled and fully coupled plate situations such as regards geometry and anisotropy of lower crustal conductors, and regions of production of lower crustal and slab related fluids. Preliminary results from a transect of 63 broad-band MT soundings across the northern South Island suggest enhanced deep crustal/uppermost mantle conductivity near the center of the island overlying a steep increase in plate dip and possible fluid release. Internal resistivity structure of the strike-slip faults is subtle and still being tested. A moderately southeast dipping mid-crustal conductor in the Westland province projects to the surface near the active Buller-Murchison thrust trend, which we tentatively correlate with damage and fluidized porosity along the deeper fault zone. This resistivity structural picture contrasts with previous study of the central South Island, where apparent continuum compression and crustal thickening creates an anisotropic conductive root zone from prograde metamorphism, fluid release and shearing.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8123 Dynamics: seismotectonics
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting