| Title | Deep Interpretation of Gravity and Airborne Magnetic Data over the Central Taupo Volcanic Zone |
|---|---|
| Authors | Supri Soengkono |
| Year | 2011 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | New Zealand, Taupo Volcanic Zone, Mesozoic greywacke basement, Quaternary volcanic infill, airbourne magnetic surveys, gravity anomalies, magnetic anomalies, three-dimensional 3D interpretation and modeling, deep magnetic body |
| Abstract | The Taupo Volcanic Zone (TVZ) is a region of Quaternary volcanic and geothermal activity in the central North Island of New Zealand. The zone is oriented SW-NE, about 350 km long and 60 km wide. It is bounded by ranges of Mesozoic sediments in the northwest and by the Kaingaroa ignimbrite plateau followed by ranges of Mesozoic sediments in the southeast. The Mesozoic sediments consist mainly of dense and indurated sandstone, siltstone and conglomerate and have been grouped together as Torlesse greywacke. The greywacke was found at 1-3 km depths beneath the TVZ volcanic infill by geothermal wells at the Kawerau, Ngatamariki, Ohaaki-Broadlands, Rotokawa and Tauhara fields, but not by wells drilled over the geothermal fields at Wairakei (maximum depth 2km) and Mokai (maximum depth 2.6 km). Gravity data are available over the whole TVZ from surveys carried out by the GNS Science (formerly DSIR) and the NZ universities since early 1950¡¯s. A regional airborne magnetic survey (1,500 m asl, 3.6 km flight-line spacing) was carried out over TVZ by the DSIR in 1952. It was followed by lower altitude surveys (800¡À100 m asl, about 1 km flight-line spacing) conducted by the Geothermal Institute (Auckland University) between 1983 and 1998 covering all main geothermal fields in the 100 km long central TVZ (between Taupo in the SW and Kawerau in the NE). Between mid-1980¡¯s and early 2000¡¯s mineral exploration companies also carried out localised but very detailed (60 m above ground, ¡Ü300m line spacing) over various parts of the TVZ. The largest detailed survey was that carried out by Glass Earth NZ Ltd in 2006 which covered more than 50% of the central TVZ area. This study presents preliminary result of new combined three-dimensional (3D) interpretation of the gravity and airborne magnetic data of the central TVZ in terms of the dense and non-magnetic Torlesse greywacke, less-dense and moderately-magnetic Quaternary volcanic infill, and deep seated magnetic bodies beneath the volcanic zone. It provides new insights into our understanding of deep (>3km depth) structure and permeability control of this fascinating volcanic and geothermal region. |