Right three years ago, on May 1983, a Symposium on Geochemical Surveillance of Volcanic and Seismic Activity was held in Palermo, Italy. In that occasion Carapezza, presenting the first report, emphasized the importance of studying the signs of impending seismic and volcanic events. What are these precursory signs? Obviously any correlations between a certain phenomenon and anomalies appearing prior to this phenomenon can be considered "precursory". However, despite some successful attempts at predicting these events by geochemical methods in various parts of the world, this approach is still neglected. The role of geochemistry should, on the contrary, be expanded and integrated with other disciplines. Classic and isotopic geochemistry may, in fact, give useful indications not only by showing anomalies considered precursory signs, but giving also parameters which are necessary to hypothesize a model of the volcanic apparatus; such a model will constitute the basic reference to evaluate possible variations of studied parameters. Applying geochemical methodologies to Pozzuoli Solfatara fluids, conclusions about their genesis and deep temperatures have been drawn. Relative ratios between non-reactive chemical species in gaseous phase, nitrogen, argon and helium, indicate an origin related to a mixing between a crustal and a mantle component. Important contributions from air-saturated water to gas emissions are thus excluded, even considering that the Solfatara water vapor is of meteoric origin as shown by its isotopic compositions. Nearest permeable outcrops are the Mesozoic limestones surrounding the impervious outcrops of the Phlegraean area; their presence at depth in the fumarole zone is indicated by the carbon isotopic composition of carbon dioxide, then where outcropping they act as recharge area to the system. As a number of geothermal wells has been drilled in the zone it has been possible to verify the applicability of isotopic geothermometers and of some gas-geothermometers when applied by a particular method. As fluids, according to experimental evidence, seem to be in chemical equilibrium at depth, changes in such a situation should be detectable by monitoring the studied parameters.
Fluid geochemistry in Phlegraean Fields area: its contribution to a geochemical model.
Bolognesi L;
1986
Abstract
Right three years ago, on May 1983, a Symposium on Geochemical Surveillance of Volcanic and Seismic Activity was held in Palermo, Italy. In that occasion Carapezza, presenting the first report, emphasized the importance of studying the signs of impending seismic and volcanic events. What are these precursory signs? Obviously any correlations between a certain phenomenon and anomalies appearing prior to this phenomenon can be considered "precursory". However, despite some successful attempts at predicting these events by geochemical methods in various parts of the world, this approach is still neglected. The role of geochemistry should, on the contrary, be expanded and integrated with other disciplines. Classic and isotopic geochemistry may, in fact, give useful indications not only by showing anomalies considered precursory signs, but giving also parameters which are necessary to hypothesize a model of the volcanic apparatus; such a model will constitute the basic reference to evaluate possible variations of studied parameters. Applying geochemical methodologies to Pozzuoli Solfatara fluids, conclusions about their genesis and deep temperatures have been drawn. Relative ratios between non-reactive chemical species in gaseous phase, nitrogen, argon and helium, indicate an origin related to a mixing between a crustal and a mantle component. Important contributions from air-saturated water to gas emissions are thus excluded, even considering that the Solfatara water vapor is of meteoric origin as shown by its isotopic compositions. Nearest permeable outcrops are the Mesozoic limestones surrounding the impervious outcrops of the Phlegraean area; their presence at depth in the fumarole zone is indicated by the carbon isotopic composition of carbon dioxide, then where outcropping they act as recharge area to the system. As a number of geothermal wells has been drilled in the zone it has been possible to verify the applicability of isotopic geothermometers and of some gas-geothermometers when applied by a particular method. As fluids, according to experimental evidence, seem to be in chemical equilibrium at depth, changes in such a situation should be detectable by monitoring the studied parameters.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
