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Authors: D'Alessandro, W.*
Brusca, L.*
Kyriakopoulos, K.*
Bellomo, S.*
Calabrese, S.*
Title: A geochemical traverse along the “Sperchios Basin e Evoikos Gulf” graben (Central Greece): Origin and evolution of the emitted fluids
Title of journal: Marine and petroleum geology
Series/Report no.: /55 (2014)
Publisher: Elsevier Science
Issue Date: 2014
DOI: 10.1016/j.marpetgeo.2013.12.011
Keywords: Rift zone
geothermal activity
Helium isotopes
Carbon isotopes
Abstract: The studied area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence of a subduction slab at depth 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). A high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 C, that discharge along the normal faults bordering the graben. In the period 2004e2012, 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions. Two main groups of thermal waters can be distinguished on the basis of their chemical composition. The first, represented by dilute waters (E.C. <0.6 mS/cm) of the westernmost sites, is characterised by the presence of CH4-rich and mixed N2eCH4 gases. The second displays higher salinities (E.C. from 12 to 56 mS/cm) due to mixing with a modified marine component. Reservoir temperatures of 150e160 C were estimated with cationic geothermometers at the easternmost sites. Along the graben, from west to east, the gas composition changes from CH4- to CO2-dominated through mixed N2eCH4 and N2eCO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (<0.1 R/RA) up to 0.87 R/RA, showing in the easternmost sites a small (3e11%) but significant mantle input. The d13C values of the CO2-rich samples suggest a mixed origin (mantle and marine carbonates).
Appears in Collections:03.02.02. Hydrological processes: interaction, transport, dynamics
03.04.06. Hydrothermal systems
03.02.03. Groundwater processes
03.04.03. Chemistry of waters
04.04.12. Fluid Geochemistry
03.04.05. Gases
Papers Published / Papers in press

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