No abstract

No abstract

No abstract

Dying and dead seas : climatic versus anthropic causes; [proceedings of the NATO Advanced Research Workshop on Dying and Dead Seas-Climatic versus Anthropic Causes,

No abstract

This study reports a complete geochemical dataset of 215 water and 9 gas samples collected in 2015 from thermal and cold discharges located in the eastern sector of the Sabatini Volcanic District (SVD), Italy. Based on these data, two main aquifers were recognized, as follows: 1) a cold Ca-HCO 3 to Ca(Na)-HCO 3 aquifer related to a shallow circuit within Pliocene-Pleistocene volcanic and sedimentary formations and 2) a deep CO 2-pressurized aquifer hosted in Mesozoic carbonate-evaporitic rocks characterized by a Ca-HCO 3 (SO 4) to Na(Ca)-HCO 3 (Cl) composition. A thick sequence of low-permeability formations represents a physical barrier between the two reservoirs. Interaction of the CO 2-rich gas phase with the shallow aquifer, locally producing high-TDS and low-pH cold waters, is controlled by fractures and faults related to buried horst-graben structures. The d 18 O-H 2 O and dD-H 2 O values indicate meteoric water as the main source for both the shallow and deep reservoirs. Carbon dioxide, which is characterized by d 13 C-CO 2 values ranging from À4.7 to þ1.0‰ V-PDB, is mostly produced by thermo-metamorphic decarbonation involving Mesozoic rock formations, masking possible CO 2 contribution from mantle degassing. The relatively low R/R a values (0.07e1.04) indicate dominant crustal He, with a minor mantle He contribution. The CO 2 / 3 He ratios, up to 6 Â 10 12 , support a dominant crustal source for these two gases. The d 34 S-H 2 S values (from þ9.3 to þ11.3‰ V-CDT) suggests that H 2 S is mainly related to thermogenic reduction of Triassic anhydrites. The d 13 C-CH 4 and dD-CH 4 values (from À33.4 to À24.9‰ V-PDB and from À168 to À140‰ V-SMOW, respectively) and the relatively low C 1 /C 2þ ratios (<100) are indicative of a prevailing CH 4 production through thermogenic degradation of organic matter. The low N 2 /Ar and high N 2 / He ratios, as well as the 40 Ar/ 36 Ar ratios (<305) close to atmospheric ratio, suggest that both N 2 and Ar mostly derive from air. Notwithstanding, the positive d 15 N-N 2 values (from þ0.91 to þ3.7‰ NBS air) point to a significant extra-atmospheric N 2 contribution. Gas geothermometry in the CH 4-CO 2-H 2 and H 2 S-CO 2-H 2 systems indicate equilibrium temperatures <200 C, i.e. lower than those measured in deep geothermal wells (~300 C), due to either an incomplete attainment of the chemical equilibria or secondary processes (dilution and/or scrubbing) affecting the chemistry of the uprising fluids. Although the highly saline Na-Cl fluids discharged from the explorative geothermal wells in the study area support the occurrence of a well-developed hydrothermal reservoir suitable for direct exploitation, the chemistry of the fluid discharges highlights that the uprising hydrothermal fluids are efficiently cooled and diluted by the meteoric water recharge from the nearby Apennine sedimentary belt. This explains the different chemical and isotopic features shown by the fluids from the eastern and western sectors of SVD, respectively, the latter being influenced by this process at a...

No abstract

No abstract