Geology topics

A. Minissale

Publications and source records attributed to A. Minissale.

4 recordsLinked to original sources

USGS1997

Multiple source components in gas manifestations from north-central Italy

Gas manifestations in north-central Italy consist of CO2-rich gases with minor N2-rich emissions and discharge either along with thermal springs or into cold and stagnant waters. 'Cold' gases are prevalently CO2-dominated (> 90%) while gases related to the thermal waters have variable composition: from CO2 > 99.5% to N2 > 90%. The variable composition of 'thermal' gases is caused by differences in the thermal regime and lithology of the ascent paths, where there is mixing of gases from multiple sources, such as N2-rich atmospheric and deep CO2-rich metamorphic end-members. Elevated concentrations of CH4 and H2 in these gases are generally related to the presence of active geothermal systems at shallow depth, such as the Larderello-Travale field in Tuscany. The ??13C values between coexisting CH4 and CO2 in all samples analyzed suggest that CH4 originates abiogenically in 200-400??C hydrothermal systems. Far from geothermal areas, where the thermal gradient is lower or the water/gas ratio is high because of large inflow of meteoric waters, H2 and CH4 are usually lower. In some cases, they can be scrubbed or oxidized (especially H2), while the residual rising gas becomes indirectly enriched in N2 and CO2. Carbon dioxide is also enriched in some discharged gases because it is produced at shallow depth in lower temperature conditions (< 150??C). Heavy ??15N values for N2 to near +7.0??? suggest that, for some gas samples that contain excess nitrogen (e.g. where N2/Ar ??? 83), this component probably derives from ammonia-rich feldspars and micas within the Palaeozoic schist basement rocks. However, other samples show evidence of a shallow component of CH4 and N2 from Neogene basin sediments. The areal distribution of the 3He/4He ratio points to a general prevalence of atmospheric and crustal 4He in the gas discharges in central Italy. A significant component of mantle 3He is only found in the geothermal areas of Larderello where the large regional thermal anomaly suggests the presence of a deep magmatic body. ?? 1997 Elsevier Science B.V.

Chemical Geology↗

USGS1997

Geochemistry of natural gas manifestions from the Upper Tiber Valley (central Italy)

Six natural gas manifestions from the upper Tiber Valley at Caprese Michelangela and Pieve S. Stefano (Arezzo) and at Umbertide (Pertugia) localities have been analysed for major, minor, trace gas compositions, as well as for ??13C in CO2 and CH4, ??15N in N2 and 3He/4He isotopic ratios. All gas emissions are CO2-rich (???94%), with N2 contents of 4-5%. Those from Caprese and Pieve S. Stefano have very peculiar compsitions when compared to other gases from northern-central Apennines. Apart from CO2, these gases show relatively high contents of He (with crustal isotopic ratios) and medium to high temperature-related gases such as CO, H2 and C6H6. Although located quite far from the geothermal areas in Tuscany, the application of several gas geothermetric techniques suggest for these gases deep equilibrium tempratures of about 300??C. Moreover, the ??13C in CO2 and CH4 (~.4.0% and -38.0%, respectively) and the ??13N values in N2 (+0.064 to +0.84%) would seem to imply a multiple deep source for these gases.

Mineralogica et Petrographica Acta↗

USGS1994

Geochemistry of thermal fluids on the volcanic isle of Pantelleria, southern Italy

Chemical analyses of thermal springs and gas emissions on the volcanic island of Pantelleria, southern Italy, suggest the presence, at depth, of a Na Cl thermal aquifer near 100°C; 80–90% of the water in this aquifer is fed by rainfall and the remainder of the mixture is seawater. Chemical analyses of the gas emissions reveal that below this shallow aquifer, a deeper hydrothermal degassing system (150°C) may exist. Rising CO 2 causes alterations of the upper aquifer host rocks (mostly pantellerites), favors formation of Na HCO 3 type waters, and causes eventual rpecipitation of CaCO 3 and coprecipitation of MgCO 3 and silica. Comparison of the present chemical data with older data from the literature suggests that the shallow Pantelleria thermal aquifer has increased in salinity and decreased in temperature during the last 25 a. Both effects were apparently caused by increased flow of recent seawater into the system because of increased ground water abstraction in the northern part of the island.

Isle of Pantelleria↗

USGS1994

In search of earthquake-related hydrologic and chemical changes along Hayward Fault

Flow and chemical measurements have been made about once a month, and more frequently when required, since 1976 at two springs in Alum Rock Park in eastern San Jose, California, and since 1980 at two shallow wells in eastern Oakland in search of earthquake-related changes. All sites are on or near the Hayward Fault and are about 55 km apart. Temperature, electric conductivity, and water level or flow rate were measured in situ with portable instruments. Water samples were collected for later chemical and isotopic analyses in the laboratory. The measured flow rate at one of the springs showed a long-term decrease of about 40% since 1987, when a multi-year drought began in California. It also showed several increases that lasted a few days to a few months with amplitudes of 2.4 to 8.6 times the standard deviations above the background rate. Five of these increases were recorded shortly after nearby earthquakes of magnitude 5.0 or larger, and may have resulted from unclogging of the flow path and increase of permeability caused by strong seismic shaking. Two other flow increases were possibly induced by exceptionally heavy rainfalls. The water in both wells showed seasonal temperature and chemical variations, largely in response to rainfall. In 1980 the water also showed some clear chemical changes unrelated to rainfall that lasted a few months; these changes were followed by a magnitude 4 earthquake 37 km away. The chemical composition at one of the wells and at the springs also showed some longer-term variations that were not correlated with rainfall but possibly correlated with the five earthquakes mentioned above. These correlations suggest a common tectonic origin for the earthquakes and the anomalies. The last variation at the affected well occurred abruptly in 1989, shortly before a magnitude 5.0 earthquake 54 km away. ?? 1993.

California↗