Magnetic Anomalies Over the Ngatamariki Geothermal Field, Taupo Volcanic Zone, New Zealand

Abstract

A low-level airborne magnetic survey (760 m covering the geothermal field in the Taupo Volcanic Zone (Central North Island of New Zealand) was undertaken in 1984. Both the normal geomagnetic field and a set of long wavelength regional magnetic anomalies were subtracted from the observed total force magnetic data toobtain secondorder residual magnetic anomalies. The second order residual anomaliesoutline localmagnetic structuresof the area and were interpreted using three-dimensional (3-D) magnetic modelling. A negative residual magnetic anomaly (about -250 over the Ngatamariki field can be explained by hydrothermally demagnetised volcanic rocks within the reservoir. A large positive anomaly (up to in the area to the west-southwest of the Ngatamariki field was modelled in terms of large concealed composite strato volcano which probably extends down to a depth of about 2 km.