Istituto di Geoscienze e Georisorse     
Cavarretta G., Gianelli G., Scandiffio G., Tecce F. Evolution of the Latera geothermal system II: metamorphic, hydrothermal mineral assemblages and fluid chemistry. In: Journal of Volcanology and Geothermal Research, vol. 26 pp. 337 - 364. Elsevier, 1985.
The Latera field (Vulsini volcanic complex, Latium, Italy) is one of the geothermal areas of the peri-Tyrrhenian belt along wich a regional, high thermal anomaly has been detected. So far nine deep wells have been drilled within the Latera caldera and four of them have been productive. The geothermal reservoir is located within the fractured carbonatic rocks of the Tuscan nappe; the overlying volcanic units, sealed by hydrothermal minerals (mainly calcite and anhydrite), act as an impervious cover. The fluids produced by the wells comes from a deep aquifers (about 100-1500m depth) wich at present is not connected with the shallow aquifer in the volcanoclastic units. Fluids temperatures range between 200 and 230C; in-hole temperatures as high as 340C at 2775m depth have been measured in dry wells. The study of the newly formed mineral assemblages from both volcanic and sedimentary units as sampled from the geothermal wells can be used to recostruct the thermal evolution of the geothermal field. The intrusion of a syenitic melt, up to a depth of about 200m, dated 0.86 My, represent the major thermal event for the units in the area and is assumed to represent the first step in the geothermal evolution of the Latera system. The above mentioned newly formed mineral assemblages can be divided into three groups:(a) "contact-metasomatic": calcite, anhydrite, diopsidic pyroxene, grossularitic garnet, phlogopite wollastonite or monticellite; (b) "high-temperature hydrothermal": calcite, anhydrite, K-feldspar, vesuvianite, melanitic garnet, tourmaline, amphibole, apidote, sulphides; (c) "low-temperature hydrothermal": calcite, anhydrite, k-feldspar, clay mineral, sulphides. Group (a) minerals are now relics. Part of (b) and all of (c) group are still in equilibrium with the existing conditions in different parts of the geothermal system. Thermodynamic calculations on the observed mineral assemblages permitted estimates of the P, T conditions and gas fugacities
URL: http://https://www.journals.elsevier.com/journal-of-volcanology-and-geothermal-research/
Subject rocks: chemical and petrographical data
petrography and mineralogy
volcanic areas: northern Latium

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