Helium isotope systematics of arc-related volcanism

The lowest arc-related He/ He ratio (0.01 Ra) is found at the transition between the east Sunda and Banda arcs in Indonesia (Hilton et al. 1992). Other arc segments with low He/ He ratios ( 1 Ra) are the Chilean Andes (Hilton et al. 1993a), Colombia (Williams et al. 1987) and the Campanian Magmatic Province of Italy (Graham et al. 1993). Therefore, in a relatively small number of samples from these localities, radiogenic helium (with He/ He ratios -0.05 Ra see Andrews 1985) dominates over any magmatic helium input. 

Location R/Ra R/Ra BMa Crustal Conv. Sediment Slab Refs  

Orthogonal convergence rate from Von Huene and Scholl (1991) 

Estimated (solid) fraction subducted (x 1000 km /Myr) from Von Huene and Scholl (1991) a = Type 1 (accretionary prism forms) b = Type 2 (no net accretion) - from Von Huene and Scholl (1991). 

Age of slab (M ) and type of crust from Jarrad (1986). Types O = oceanic C = continental T = transitional. 

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