Helium-3 evidence for a spot of thinned lithosphere in the eastern part of the Balkan Peninsula

Abstract

The presence of a mantle component in the crust-to-atmosphere volatile flux may be considered as evidence for increased crustal permeability. The air-corrected 3He/4He = R ratio, usually normalized to Rair, is well known as a starting point for such an evaluation.The relative abundance of 3He, however, may be underestimated especially in the case of helium-rich fluids. The 3He/20Ne ratio is proposed as an alternative geochemical tracer for mantle exhalation, normalizing the 3He abundance to a small and comparatively constant atmospheric component: neon. The 3He/20Ne ratio for 21 mineral water sites from the eastern part of the Balkan peninsula are calculated on the bases of previous measurements. The regional distribution of the values found is compared with the data available on the depth of Moho discontinuity and lithosphere/asthenosphere boundary. An evident correlation between 3He/20Ne maximum values and an area with thin lithosphere is observed.