A geochemical traverse along the 'Sperchios Basin - Evoikos Gulf' graben (Central Greece): Origin and evolution of the emitted fluids

The studied area is a 130km 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 2004-2012, 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.