L ike most of the Balkan Peninsula, North Macedonia is a geodynamically active area. As such it hasmany hydrothermal features and gas manifestations. Until now, no systematic study about thegeochemical characterization of the geogenic gases was made before in this country. In August2019, 24 gas samples were collected in the study area. All, except one collected at Duvalo (soil gas),are gases bubbling or dissolved in thermomineral waters (temperatures from 12 to 66 °C). Theywere analysed in the laboratory for their chemical (He, Ne, Ar, O2 , N2 , H2 , H2S, CH4 and CO2) andisotopic composition (δ13C-CO2, δ13C-CH4, δ2H-CH4 and R/RA). Most of the gases have CO2 as themain component (400-998,000 ppm) while the remaining are enriched in N2 (1300-950,000 ppm).Helium ranges from 0.3 to 2560 ppm while CH4 from 1.6 to 20,200 ppm. R/RA and 4He/20Ne ratiosindicate a generally low atmospheric contamination, a prevailing crustal contribution and mantlecontributions between 1 and 20% considering a MORB endmember. The highest mantlecontributions are found in the SE part of the country very close to the sites that show the highestR/RA values in continental Greece . This area is characterised by extensional tectonics and Plio-Pleistocene volcanism. A quite high mantle contribution (about 15%) is also found in twomanifestations in the NW part of the country along a main normal fault system. With the exceptionof the sample of Smokvica, which has very low CO2 (1400 ppm) and δ13C-CO2 (-15.7 ‰ V-PDB), allfree gases show a relatively narrow range in δ13C-CO2 values (-4.6 to +1.0 ‰ V-PDB) indicating themixing between a mantle and a carbonate rock source. The isotope composition allows us toassign the CH4 origin to three sources. The largest group can be attributed to a hydrothermalorigin (δ13C-CH4 around -20 ‰ V-PDB and δ2H-CH4 around -100‰). Three samples collected in theSW part of the country have a thermogenic origin (δ13C-CH4 around -35 ‰ V-PDB and δ2H-CH4around -160‰ V-SMOW). Finally, one sample (Smokvica) with the highest values (δ13C-CH4 -7.2 ‰V-PDB and δ2H-CH4 -80‰ V-SMOW) may be attributed to abiotic processes in a continentalserpentinization environment or to methane oxidation.
|Numero di pagine||2|
|Rivista||GEOPHYSICAL RESEARCH ABSTRACTS|
|Stato di pubblicazione||Published - 2020|