Electrical structure along a transect of the central South Island, New Zealand

Regional magnetotelluric responses from a transect across the central South Island, New Zealand, have been inverted to produce a smooth two-dimensional model of electrical resistivity structure associated with the Southern Alps orogen. The resulting structure is consistent with proposed models for the orogen and shows a zone of enhanced conductivity at a depth of only 10 km beneath the Southern Alps. This can be interpreted as being caused by the presence of ''wet'' greenschist facies rocks upthrust from lower crustal depth. There is some indication of reduced resistivity at 25 km depth beneath the Canterbury Plains, which may be associated with the existence of a lower crustal detachment surface. A large resistivity contrast occurs near the Alpine Fault, and this may be an indication of a lack of lateral fluid movement across the fault zone.