FY 1994

Helium isotopes in some historical lavas from Mount Vesuvius

Graham, D.W., P. Allard, C.R.J. Kilburn, F.J. Spera, and J.E. Lupton

J. Volcanol. Geoth. Res., 58, doi: 10.1016/0377-0273(93)90117-A, 359–366 (1993)

He/He ratios in lavas erupted during the last 360 years at Mt. Vesuvius are between 2.2 and 2.7 R (R = atmospheric ratio of 1.39 × 10), and are among the lowest values measured in young volcanic rocks. They are also identical to values measured in summit crater fumaroles sampled during 1987-1991. This agreement indicates that the He/He ratio in the crater fumaroles faithfully tracks the magmatic value. The relatively low and uniform He/He ratio in the lavas reflects either a mantle source enriched in (U + Th)/He, or a mixture of magmatic and crustal components.