Origin of Helium and Associated Fluid in Fault‐Related Hydrothermal Systems of the Eastern Pyrenees.

ABSTRACT Intense hydrothermal activity hosted by regional tectonic structures occurs in the Eastern part of the Pyrenees. Helium isotope ratios (3He/4He) in hot springs along the Têt (0.033–0.099 Ra) and the Tech (0.171–0.375 Ra) faults indicate different signatures from purely crustal to slightly contaminated by magmatic helium. 3He/4He ratio increased towards the East, consistently with the observed thinning of the continental crust. These results suggest localised and not interconnected hydrothermal systems at fault scale. The origin of magmatic helium contamination is discussed in the light of the Gulf of Lion geodynamic evolution and data from comparable orogenic hydrothermal systems in the Alps. [ABSTRACT FROM AUTHOR]