Publication Date:
2017-04-04
Description:
The study area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes
both the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in
the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). Its
high geothermal gradient is evidenced by the presence of many thermal springs with temperatures from 19 to 82
C, issuing along the normal faults bordering the graben.
In the period 2004-2012 about 50 gas and water samples have been collected and their chemical and isotopic analysis
revealed a wide range of compositions.
Going from west to east the gas composition changes from CH4- to CO2-dominated passing through mixed N2-
CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal
values (0.05 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but
significant mantle input. Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples
and hydrothermal origin for the remaining samples. Positive 15N values indicate a contribution of crustal derived
nitrogen for the N2-rich samples. The 13C values of most the CO2-enriched samples show a mixed origin (mantle
and marine carbonates).
Also the chemical composition of the waters shows differences along the graben and two main groups can be separated.
The first, represented by dilute waters (E.C. 〈 600 S/cm), is found in the westernmost sites characterised
by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (E.C. from
12 to 56 mS/cm) due to the mixing with a modified marine component. Only the water composition of easternmost
sites in the Giggenbach’s cation triangular graph plots in the field of the partially equilibrated waters giving
estimated temperatures at depth of 150-160 C.
Description:
Published
Description:
Vienna, Austria
Description:
4.5. Studi sul degassamento naturale e sui gas petroliferi
Description:
open
Keywords:
hydrothermal systems
;
gas chemistry
;
water chemistry
;
stable isotopes
;
03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters
;
03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
;
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Abstract
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