| Title | Distribution, Age and Hydrothermal Alteration of Quaternary Volcanic Rocks in the Taupo Volcanic Zone (North Island, New Zealand) Seen from High Resolution Airborne Magnetic Data |
|---|---|
| Authors | Supri Soengkono |
| Year | 2013 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Airborne magnetic survey, reduction to the pole (RTP), first vertical derivative (1VD), analytic signal (ASig), lavas, welded ignimbrites, geothermal fields, reversely magnetized rocks |
| Abstract | High resolution airborne magnetic data over the central part of TVZ were interpreted in a simple and direct way using some standard magnetic anomaly processing techniques to assess the distribution, general age and hydrothermal alteration of the Quaternary volcanic rocks in this area. The magnetic anomalies were first “reduced to the pole”. This standard magnetic processing moves centres of anomaly to positions above their sources. In region of Quaternary volcanic rocks such as TVZ, high values of reduced to the pole (RTP) anomalies (magnetic highs) often mark the locations of lavas and welded ignimbrites. Two other types of magnetic processing techniques known as the “first vertical derivative” and “analytic signal” were used to help identify anomalies associated with near surface sources. The GNS Schlumberger apparent resistivity data across TVZ were used to identify magnetic lows (low values of RTP anomalies) that are likely to be associated with hydrothermal alterations of the volcanic rocks, including those by systems that are no longer active. The resistivity data were also used to detect magnetic lows that could be caused by older ( more than 730ka), reversely magnetised volcanic rocks This direct interpretation indicates that older ( more than 730ka) volcanic rocks are widespread in the TVZ. The results also demonstrate the value of airborne magnetic survey in the exploration and investigation of geothermal systems in a Quaternary volcanic area. Similar interpretation can be applied to other geothermal systems hosted by young volcanic rocks elsewhere. Airborne magnetic data are often already available over geothermal fields worldwide from surveys conducted by government agencies or mineral exploration companies. |