Wide-band magnetotelluric measurements across the Taupo Volcanic Zone, NewZealand - Preliminary results

The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by intensive geothermal activity and frequent rhyolitic volcanism. Sixteen wideband (0.0 1-1,800 s) magnetotelluric soundings were measured along a 110 km-long prof ile approximately perpendicular to the strike of the TVZ. A model obtained from 2D inversion of the soundings shows two near-surface regions of high c onductance 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. Modelli ng 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 in dicate the presence of connected melt. At greater depth (20-30 km) the uppe r mantle beneath the TVZ appears to be anomalously conductive, consistent w ith observed high seismic attenuation.