Publication Date:
2017-04-04
Description:
The first geochemical data showing the existence of an active degassing activity over a large seismically
active sector of the Southern Alps (Friuli Region, NE Italy) are presented. The dissolved gases, helium and
carbon isotopic systematics of 46 water samples taken from 13 sites running along E–W and NE–SW faults
besides the natural degassing of a 5000 km2 wide area are investigated. The chemical composition of the
dissolved gases revealed that a CO2-rich gas phase feeds the local groundwaters. 3He/4He ratios (R)
normalized to the atmospheric 3He/4He ratio (Ra=1.39×10−6) and corrected for the atmospheric
contamination (R/Rac), range from 0.29 to 1 as a result of a two component (radiogenic and atmospheric)
mixing. The δ13C values of total dissolved inorganic carbon (TDIC) ranging from −15.28 to −0.75‰ vs. PDB,
show the occurrence of multiple gas–water interactions. The mixing between the atmospheric air and a
crustal source and the gas–water interactions occurring at various extents appears to be the main control on
the observed He–C systematics. The natural CO2 degassing was evaluated by a soil gas survey carried out by a
grid of about 100 measuring sites located over the area that generated destructive seismic sequences (e.g. the
Gemona sequence of 1976; main shocks M6.4 of 6th May and M6.1 of 11th and 15th September). The results
obtained show that a significant amount of crustal-originated gases are released over the continental area of
Eastern Southern Alps. The evidence that carbon dioxide is associated with radiogenic-type helium denotes
the lack of the mantle as primary energy and degassing source, highlighting the possibility that CO2 is
produced by thermo-mechanical processes occurring at seismogenic depth. The information provided here
may be used to start up a long-term geochemical monitoring of this seismically active area and could be able
to detect the modifications occurring to the circulating fluids to gain a better insight on the relationships
between the fluids' geochemistry and the activity of the local seismogenic faults.
Description:
Published
Description:
76–85
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
reserved
Keywords:
Fluids
;
Faults
;
geochemistry
;
isotopes
;
04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
