Exhumation of an active magmatic–hydrothermal system in a resurgent caldera environment: the example of Ischia (Italy)

Ischia is a rare case of a well-exposed caldera system that has experienced rapid recent resurgence, which can be used to dissect the anatomy of an otherwise inaccessible active hydrothermal system developed in a caldera-forming environment. Integrated analyses of melt and fluid inclusions, mineralogy and stable isotopic compositions of pumices, tuffs and syenitic xenoliths of the Ischia volcanic system provide strong physico-chemical constraints on the shallow magmatic reservoir and the hydrothermal system. The hydrothermal system has been exposed by the rapid uplift of the Mt. Epomeo resurgent block. The engine of the hydrothermal system of Ischia can be identified in the shallow magmatic system (at around 2 km depth) that hosts hot (c. 1000 °C) trachytic magma. The hydrothermal system developed principally within thick intracaldera ignimbrite deposits, and extended to a depth of at least 1 km, defining a series of facies characterized by associations of alteration mineral assemblages typical of a seawater-dominated high-temperature geothermal system.