MANTLE PLUME HELIUM IN SUBMARINE BASALTS FROM THE GALAPAGOS PLATFORM

Helium-3/helium-4 ratios in submarine basalt glasses from the Galapago s Archipelago range up to 23 times the atmospheric ratio in the west a nd southwest. These results indicate the presence of a relatively unde gassed mantle plume at the Galapagos hot spot and place Galapagos alon gside Hawaii, Iceland, and Samoa as the only localities known to have such high helium-3/helium-4 ratios. Lower ratios across the rest of th e Galapagos Archipelago reflect systematic variations in the degree of dilution of the plume by entrainment of depleted material from the as thenosphere. These spatial variations reveal the dynamics of the under lying mantle plume and its interaction with the nearby Galapagos Sprea ding Center.