Hydrogeochemistry of the region between Monte Amiata and Rome

Abstract

The study carried out in the region limited by the Mt. Amiata zone to the north, the river Tiber to the east and SE, Rome to the south and the Tyrrhenian sea to the west, is aimed at investigating the thermal and mineral manifestations from the hydrogeological and geochemical point of view. These manifestations (about 200 in all) are distributed over an area exceeding 5000 km 2. The investigation enabled to locate the areas of possible supply of meteoric waters and to determine the pattern of underground circulation down to a depth of approximately 1000–1200 m. Consequently, the most preferential areas as possible reservoirs of hyperthermal fluids have been singled out. In this connection, some ions or compounds such as boron, silica, chlorine, magnesium and sulphates proved to be particularly significant. Generally speaking, thermomineral manifestations represent the surface trace of two essential types of circulation: one, occurring almost exclusively within the volcanic cover (2–300 m at most) and the other, deeper, prevalently involving the calcareous Mesozoic substratum at various levels (6–700 m at least). Because of particular lithological and tectonic situations, more or less marked mixings occur locally between the above-said types of circulation, From such mixings a series of different effluents, which feature chemical and thermal characteristics intermediate between those of the meteoric waters and those of the deep thermomineral waters, originates.