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Titel |
The fluids' geochemistry along the "Sperchios Basin - Northern Evoikos Gulf" Graben, a geodynamically complex area of Central Greece |
VerfasserIn |
Walter D'Alessandro, Sergio Bellomo, Lorenzo Brusca, Sergio Calabrese, Konstantinos Kyriakopoulos |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250073699
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Zusammenfassung |
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 δ15N values
indicate a contribution of crustal derived nitrogen for the N2-rich samples. The δ13C
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 μS/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. |
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