Mantle-Helium Distribution in Western Anatolia, Turkey: Relationship to Heat Distribution, Active Extension and

Western Anatolia comprises one of the world’s best known extensional terrains and is characterized by the presence of several moderate- to high-enthalpy geothermal fields located along the boundary faults of the major grabens. Helium-isotope compositions of geothermal fluids reflect mixing between mantle (3He/4He = 8RA where RA = air 3He/4He; [1]) and crustal (3He/4He < 0.1RA; [2]) components, the former ranging up to 45 % of the total helium in a given sample. There is a general positive correlation between the distribution of heat and helium in western Anatolia