Links Between Volcanic, Tectonic and Geothermal Systems Shown by Array Mt Data in the Taupo Volcanic Zone, New Zealand

Abstract

The Taupo Volcanic Zone (TVZ) is an actively rifting volcanic arc, characterised by recent rhyolitic volcanism, large collapse calderas and more than 20 high-temperature liquid-dominated geothermal systems that convectively discharge ~ 4 GW of heat. During the past 6 years, over 500 broadband magnetotelluric (MT) measurements (at 2 km site spacing) have been made that form two arrays in the northern and southern parts of the central TVZ. 3-D inversion models of these data provide a detailed picture of the electrical resistivity structure of the brittle upper crust, and clarify the relationship between the underlying magmatic system and the overlying system of hydrothermal (convective) heat transport.
In particular, the majority of the geothermal fields encompassed by these MT data are associated with deep low-resistivity zones located at the margins of low-gravity anomalies. This association suggests that geological structure (in particular collapse calderas) and shallow magmatic intrusions play a more direct role in the pattern of convective heat transport than previously envisaged. While several of the geothermal fields appear to be underlain by shallow (~3 km depth) bodies of crystallising magma, others are not. A model of episodic intrusion in a region focused around the geothermal fields is consistent with both the resistivity structure and geological evidence for temporal changes at the geothermal fields in response to nearby magmatic events.