Traditional and isotopic geochemical studies conducted on the fluids from Pozzuoli Solfatara have led to new and interesting conclusions concerning the origin of the fluids and their T at depth. The isotopic composition of the steam suggests that the latter is the result of boiling of meteoric water which had previously interacted with the rocks and remained underground for >30 years. This conclusion contradicts the previously held theory that the steam was originally sea-water within the volcanites. The recharge areas are identified as the limestone units in the region. On the basis of the C isotopic composition, the CO2 would appear to derive mainly from the thermometamorphism of marine carbonates, with some CO2 of magmatic origin. Nitrogen and helium are clearly of non-atmospheric origin, considering their very high Ar ratios, which are mostly the result of radiogenic processes. Application of gas chemical and isotopic geothermometers has led to the definition of several different temperature intervals for different depth intervals, in agreement with the data obtained through measurements in the geothermal borehole in this zone.
Studi di geochimica tradizionale ed isotopica effettuati sui fluidi emessi alla Solfatara di Pozzuoli hanno permesso di trarre conclusioni nuove ed interessanti sulla genesi dei fluidi stessi e delle temperature profonde. Dalla composizione isotopica del vapore si e' dedotto che questo si origina per ebollizione di acqua meteorica gia' fortemente interagita con le rocce e rimasta nel sottosuolo per oltre 30 anni. Questa conclusione capovolge quanto precedentemente accettato in letteratura e cioe' che il vapore si originasse da acqua di mare contenuta nelle vulcaniti; viene inoltre ipotizzato che le aree di ricarica siano rappresentate dagli affioramenti calcarei presenti nella regione. Sulla base della composizione isotopica del carbonio, si ritiene che l'anidride carbonica derivi essenzialmente dal termometamorfismo di rocce carbonatiche marine con apporti di anidride carbonica di origine magmatica. L'azoto e l'elio sono chiaramente di origine non atmosferica, dati i loro elevatissimi rapporti con l'argon, prodotto a sua volta in gran parte da processi radiogenici. L'applicazione di geotermometri chimici a gas ed isotopici ha permesso di ipotizzare distinti intervalli di temperatura attribuibili a diversi ambienti profondi e concordanti con le misure effettuate nei pozzi geotermici della zona.
Studio chimico ed isotopico della Solfatara di Pozzuoli: ipotesi sull'origine e sulle temperature profonde dei fluidi.
L Bolognesi;
1986
Abstract
Traditional and isotopic geochemical studies conducted on the fluids from Pozzuoli Solfatara have led to new and interesting conclusions concerning the origin of the fluids and their T at depth. The isotopic composition of the steam suggests that the latter is the result of boiling of meteoric water which had previously interacted with the rocks and remained underground for >30 years. This conclusion contradicts the previously held theory that the steam was originally sea-water within the volcanites. The recharge areas are identified as the limestone units in the region. On the basis of the C isotopic composition, the CO2 would appear to derive mainly from the thermometamorphism of marine carbonates, with some CO2 of magmatic origin. Nitrogen and helium are clearly of non-atmospheric origin, considering their very high Ar ratios, which are mostly the result of radiogenic processes. Application of gas chemical and isotopic geothermometers has led to the definition of several different temperature intervals for different depth intervals, in agreement with the data obtained through measurements in the geothermal borehole in this zone.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
