Evidence on the development of a wide high-T hydrothermal system in the Ischia volcanic field before Mt. Epomeo resurgence: new insights from investigation of hydrothermally altered lithic clasts of Secca d’Ischia volcanic deposits

Abstract

 This work is focused on the hydrothermal system developed in the Ischia volcanic field before Mt. Epomeo resurgence, and is based on the investigation of hydrothermally altered lithic clasts present in the volcanic deposits of Secca d’Ischia and Epomeo Green Tuff eruptions. We demonstrate that a wide high temperature hydrothermal system occurred in the Ischia volcanic complex, both in intracalderic and extracalderic areas, at the time of the caldera-forming paroxysmal phase (60-56 ka). This hydrothermal system was characterized by high temperatures ranging from 240 °C and 340 °C and fluids of marine (~3.5 wt% NaClequiv.) and meteoric origin (<0.5 wt% NaClequiv.). In the intracalderic area, the hydrothermal system was exhumed during the resurgence of Mt. Epomeo; in the extracalderic area of the island the hydrothermal system was at least partially disrupted during the Secca d’Ischia eruption.