3D magnetotelluric imaging of a transcrustal magma system beneath the Campi Flegrei caldera, southern Italy

Abstract Magnetotelluric investigations can reconstruct features within magmatic systems, such as the distribution of melt and fluid and the volcano-tectonic structures. Here, we use this approach to image the subsurface beneath the active Campi Flegrei caldera, providing new details on the crustal structure down to 20 kilometers. The imaging shows a multilevel magmatic architecture controlled by deep and shallow volcano-tectonic structures. The magma plumbing system primarily manifests as a low resistivity anomaly located at 8–20 kilometers depth and interpreted as a mid-lower crustal mush zone containing ~10% melt. This zone transitions upwards through a channel-like low resistivity structure containing ~8% of melt and a medium resistivity sector where small lenses of heterogeneously distributed magma accumulate and cool. Our new subsurface imaging attests to a transcrustal mush system that has been revealed beneath Campi Flegrei, with important implications for interpretation of monitoring data at one of the world’s most hazardous caldera.