Geothermal exploration of Roccamonfina volcano, Italy

Abstract

The Quaternary volcano of Roccamonfina, located within the Roman high-potassic province, developed in the time interval 1.5-0.25 Ma, initially as a stratocone which later was partially destroyed by phreatomagmatic explosions. The last evolutionary stage is represented by intra-crater latite domes and trachybasalt flows ( ca. 15 Ma). Geophysical data, primarily from gravity and MT/EM surveys, demonstrate that the volcano formed at a complex structural intersection above a NE-trending Pliocene graben. The same data, confirmed by the result of an 887 m test well, indicate that the volcano has not undergone caldera subsidence of the type exemplified by the Valles Caldera of New Mexico, but more probably had a series of post-stratocone lateral blasts akin to the 1980 Mount St. Helens eruptions. Hot springs near the western foot of the volcano, and the presence of young highly-evolved rocks suggested that the area could have geothermal potential. However, geochemical and isotopic data provide no indication of the present existence of a hydrothermal system, whilst the lack of alteration (both at the surface and in the test well) suggest that no such system existed in the past. Geophysical data show no anomalous features which might be associated with a geothermal reservoir or with hydrothermal alteration. These negative conclusions, strongly supported by the low temperature of the test well (35°C at 886 m), demonstrate fairly conclusively that Roccamonfina is non-prospective for high-enthalpy geothermal resources.