Magnetotelluric Imaging of Pantelleria Caldera: Implications for its Active Structures

Pantelleria island is the emerged part of a volcanic structure extending in the NW-SE direction for nearly 135 km, with 31.7 km being the emerged portion. The main eruptive vents of Pantelleria develop along NW-SE structures, while another relevant structural system follows a NNE-SSW trend. Pantelleria volcanic activity, characterized by peralkaline rhyolitic (pantelleritic) magmatism, generated large caldera forming explosive events and low-magnitude eruptions including lava flow. Recent submarine basaltic eruptions (Banco di Graham 1831; Foerstner volcano, 5 km NW of the island, in 1891), together with ongoing hydrothermal emissions and fumaroles field, indicate that Pantelleria’s magmatic system is still active. Fumaroles and diffused CO2 emissions from the soil are widespread on the island with manifestations of rather high temperature concentrated in the central part of the island, and lower temperature manifestations (30°C) near the shore of Lago di Venere volcanic lake. In particular, the most powerful fumaroles manifestation is located in the Favare area, where soils are deeply altered because of high temperatures (up to 100°C) and anomalous hydrothermal gas fluxes. Despite this hydrothermal activity, no studies have been devoted to understand the structural framework of the Pantelleria caldera and the control exerted by the main structure on geothermal reservoirs and/or fluid circulation. The lack of geophysical tomographies represents a significant gap in reconstructing the subsurface of the caldera and its deep structures, including the geothermal system and volcano-tectonic features. This study addresses this gap by employing a short-period magnetotelluric (MT) survey, a powerful tool for identifying the role and distribution of geothermal fluids and their interactions with main structural lineaments and surrounding rock volumes. MT data, collected from seventy-eight on-shore soundings, allowed us to characterize the subsurface electrical resistivity, which was used to obtain a 3D model of electrical resistivity, revealing the main structures of Pantelleria down to a depth of 2.5 km. Integrating geological and geochemical datasets, the study delineates resistivity variations associated with volcanic structures, hydrothermal alterations, and possible magmatic signature. The imaging of the deep sector of the Island shows different resistivity anomalies that provide fundamental information on the geometry and volume of possible geothermal reservoirs, as well as insights into the interaction between lithostratigraphic setting, fluid circulation, and current hydrothermal activity. Vertical and lateral resistivity contrasts also highlight the main volcano-tectonic features such as the caldera boundary. Low resistivity anomalies dominate within the caldera, while a more resistive environment characterizes the external zones of the island. The 3D resistivity model significantly improves the understanding of Pantelleria’s volcanic and geothermal processes and supports further research aimed at estimating the geothermal potential of the island.