Three‐dimensional electrical resistivity image of magma beneath an active continental rift, Taupo Volcanic Zone, New Zealand

Abstract

Magmatic activity in regions of continental extension may result in huge (>400 km 3 ) explosive eruptions of viscous, gas‐rich silicic‐magma. Geochemical and geological data suggest that the large volumes of magma erupted are produced by extracting interstitial liquid from a long‐lived ‘mush zone’ (a mixture of solid crystals and liquid melt) that accumulates in liquid‐dominated lenses at the top of a much thicker region of lower melt‐fraction mush. Such lenses will be highly electrically conductive compared with normal mid‐crustal rocks. Here we use results of 220 magnetotelluric (MT) soundings to construct a 3‐D electrical resistivity image of the northern (silicic) part of New Zealand's Taupo Volcanic Zone, a young continental rift associated with very high heat flow and intense silicic volcanism. The electrical resistivity image shows a plume‐like structure of high conductivity, interpreted to be a zone of interconnected melt, rising from depths >35 km beneath the axis of extension.