Wide‐band magnetotelluric measurements across the Taupo Volcanic Zone, New Zealand‐Preliminary results

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Abstract
The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by intensive geothermal activity and frequent rhyolitic volcanism. Sixteen wide‐band (0.01–1,800 s) magnetotelluric soundings were measured along a 110 km‐long profile approximately perpendicular to the strike of the TVZ. A model obtained from 2D inversion of the soundings shows two near‐surface regions of high conductance which correspond to low density volcaniclastic sediments, up to 3 km thick, which infill a sequence of collapse calderas. At deeper levels (approximately 5–10 km) a resistive layer underlies the entire TVZ. Modelling shows other conductive zones occur beneath the TVZ, with the shallowest lying below the central part at a depth of 10–15 km. Given the high heat flux and volcanic history of the TVZ, the high conductivity at depth may indicate the presence of connected melt. At greater depth (20–30 km) the upper mantle beneath the TVZ appears to be anomalously conductive, consistent with observed high seismic attenuation.