HR: 0830h
AN: T51F-0211    [PDF]
TI: Crustal and Upper Mantle Structure of the Taupo Volcanic Zone, North Island, New Zealand.
AU: * Harrison, A J
EM: harrison@esc.cam.ac.uk
AF: University of Cambridge, Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: White, R S
EM: rwhite@esc.cam.uk
AF: University of Cambridge, Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AB: The Taupo Volcanic Zone (TVZ) is a major Pliocene-Quaternary NNE-SSW orientated,volcano-tectonic complex, about 250 km long and up to 60 km wide in the central North Island of New Zealand. The TVZ is one of the largest and most frequently active rhyolitic magmatic systems on Earth, characterised by intense shallow seismic activity, high natural heat flow (some 12-20 times the continental norm) and active NW-SE extension. To the north of the TVZ, subduction of the Pacific Plate beneath the oceanic lithosphere of the Australian Plate is accompanied by a region of back-arc extension (the Havre Trough). The TVZ marks the southern continuation of this back-arc extension into continental lithosphere.The TVZ therefore represents an ideal opportunity to study the onset of back-arc spreading onshore. Here we present forward and inverse models of the crustal structure beneath the TVZ. These models incorporate both active and passive source data acquired from the NIGHT (North Island GeopHysical Transect) project. Common to both models is a 2-3km deep basin of low velocity sediments which we interpret to be ignimbrite deposits. Typical basement velocities of $\sim$6km/s are observed beneath and to either side of the TVZ, where they correlate well with mapped outcrops of basement rocks. Velocities of around 7.3 km/s are observed at depths greater than 16 km beneath the TVZ. Such velocities may be interpreted as anomalously low velocity upper manlte or heavly intruded lower crust. Having constrained the crustal structure we then use earthquake events from the subducting Pacific Plate to yield information on the velocity structure of the upper mantle beneath the TVZ. NIGHT Working Group A. Harrison, J. Haines, R. White (University of Cambridge,United Kingdom); S. Henrys, S. Bannister, I. Pecher, F. Davey (Inst. Geological and Nuclear Sciences, Lower Hutt, New Zealand); T. Stern, W. Stratford (Victoria University of Wellington, New Zealand); H. Shimamura, Y. Nishimura, and A. Yamada (Hokkaido University, Sapporo, Japan).
DE: 7205 Continental crust (1242)
DE: 8105 Continental margins and sedimentary basins
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting