Resistivity structure of western Taupo Volcanic Zone, New Zealand

Abstract

data from two deep-penetration electrical resistivity surveys crossing the western margin of the Taupo Volcanic Zone (TVZ) near Tihoi, northwest of lake Taupo, North island, New Zealand, have been used to identify the elements of the margin. in this vicinity the volcanologically defined boundary of the TVZ includes the andesitic cones of Pureora and Titiraupenga. The faulted margin of the TVZ lies east of these cones and is marked in the resistivity data by a dipping interface (faulted margin) between the resistive greywacke rocks to the west and the relatively conductive volcanic rocks that fill the upper few kilometres of the TVZ. The resistivity and gravity signatures of the margin are coincident in this vicinity. To the immediate east of the margin is a low-resistivity zone c. 10 km wide and 2.5 km deep. The low-resistivity material within this region is identified as old (>1 Ma) volcaniclastics that contain clays produced by low-temperature alteration and devitrification. This material is reversely magnetised. we suggest that this zone was formed following the onset of active extension of the TVZ and has since remained relatively undisturbed while the focus of volcanism and deformation has moved to the east. The eastern boundary of this low-resistivity zone coincides with the western edge of the whakamaru caldera (the boundary of the "young TVZ"). although the resistivity data can be matched using an interface with a dip to either the east or west, an eastward dip would be consistent with the boundary having been formed during the collapse associated with the formation of the whakamaru caldera. The resistivity signature within the whakamaru caldera is consistent with >2 km thickness of younger, more resistive volcanic sequences, suggesting the low-resistivity layers found to the west have been disrupted and downfaulted to be replaced with young, resistive caldera infill.

Rapid Evolution of Subduction‐Related Continental Intraarc Rifts: The Taupo Rift, New Zealand

“…Shallow subsurface studies also support inward fault migration over time. On the western margin of the young rift, large fault throws in post‐350 ka deposits have been proposed based on resistivity data (Bibby et al, ) (location 11 in Figure b and Text S1), suggesting extensive faulting between 350 ka and 25–18 ka. Likewise, large displacements of ~350 ka old deposits sealed by ~230 ka old deposits have been interpreted on the eastern side based on seismic reflection and gravity data (Stagpoole, ) (location 6 in Figure b and Text S1).…”

Mechanical and physical properties of hydrothermally altered rocks, Taupo Volcanic Zone, New Zealand

“…1: Wilson et al, 1995;Rowland and Sibson, 2001), and in its modern form coincides with a structurally and magmatically segmented rift system (Taupo rift). The oblique subduction of oceanic crust from the Pacific plate beneath the Indian-Australian plate caused the back arc/arc basin producing the TVZ (Cole, 1990;Bibby et al, 1995Bibby et al, , 2008Darby et al, 2000;Rowland and Sibson, 2004;Cole and Spinks, 2009;Seebeck et al, 2010;.…”

Comparison of DC sensitivity patterns for anisotropic and isotropic media

“…The emerging trend is for tensor measurements, in which the impressed electric field (from the current electrodes) is sequentially applied in two orthogonal directions, and the voltage measurements made on two orthogonal sets of potential electrodes (Caldwell and Bibby, 1998;Novák et al, 2004;Bibby et al, 2008).…”