Lithospheric structure of an active back-arc basin: The Taupo Volcanic Zone, New Zealand

Harrison, A. J. and White, R. S. (2006) Lithospheric structure of an active back-arc basin: The Taupo Volcanic Zone, New Zealand. Geophysical Journal International, 167 (2). pp. 968-990. DOI

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Seismic data from both explosive and earthquake sources have been used to model the crustal and upper-mantle velocity structure beneath the Taupo Volcanic Zone (TVZ), an active backarc basin in central North Island, New Zealand. Volcanic sediments with P-wave velocities of 2.0–3.5 km s−1 reach a maximum thickness of 3 km beneath the central TVZ. Underlying these sediments to 16 km depth is material with velocities of 5.0–6.5 km s−1, interpreted as quartzo-feldspathic crust. East and west of the TVZ, crust with similar velocities is found to depths of 30 and 25 km, respectively. Beneath the TVZ, material with P-wave velocities of 6.9–7.3 km s−1 is found from 16 to 30 km depth and is interpreted as heavily intruded or underplated lower crust. The base of the crust at 30 km depth under the TVZ is marked by a strong seismic reflector, interpreted as the Moho. Modelling of arrivals from deep (>40 km) earthquakes near the top of the underlying subducting Pacific Plate reveals a region with low mantle velocities of 7.4–7.8 km s−1 beneath the crust of the TVZ. This region of low mantle velocities is best explained by the presence of partially hydrated upper mantle, resulting from dehydration of hydrous minerals (e.g. serpentinite) carried down by the underlying subducting plate. Within the lower crust beneath the TVZ, a region of high (0.34) Poisson's ratio is observed, indicating the presence of at least 1 per cent partial melt. This melt probably fractionates and assimilates crustal material before some of it migrates into the upper crust, where it provides a source for the voluminous rhyolitic magmas of the TVZ.

Item Type: Article
Uncontrolled Keywords: 2006 AREP IA49 IA52 2006 P
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
02 - Geodynamics, Geophysics and Tectonics
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Geophysical Journal International
Volume: 167
Page Range: pp. 968-990
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:02
Last Modified: 23 Jul 2013 10:07

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