Exhumation of an active magmatic-hydrothermal system in a resurgent caldera environment. The example of Ischia Island (Italy)

Abstract: Ischia island is a rare case of well-exposed, rapid ongoing caldera resurgence that can be used to dissect the anatomy of rarely exposed active hydrothermal systems developed in the caldera forming environment. An integrated approach (melt and fluid inclusions, mineralogy, stable isotopes) was used on the pumices, tuffs and syenitic xenoliths of Ischia volcanic system to provide strong physico-chemical constraints on the shallow magmatic reservoir and the hydrothermal system. The latter is partially exposed on the surface due to the rapid uplift of the Mt. Epomeo resurgent block. The engine of the hydrothermal system of Ischia island can be identified in the shallow (top at around 2 km of depth) and wide magmatic system that hosts hot (around 1000°C) trachytic melts. The hydrothermal system developed within thick intracaldera ignimbrite deposits, and the most external portions of the subvolcanic bodies, to a depth of at least 1 km defining a secondary mineralogical distribution typical of high temperature geothermal systems dominated by seawater.