Noble gas isotope and halogen compositions of chromian spinels within beach sand from Gorgona Island, Colombia

Abstract

Here we report noble gas isotope ratios and halogen compositions of chromian spinels collected from the beach sands of Gorgona Island, Colombia. Isotope ratios of helium (³He/⁴He) trapped in melt inclusions in chromian spinels are estimated to be higher than 20 Ra (Ra is atmospheric ³He/⁴He), suggesting that the Galapagos mantle plume, with the highest reported ³He/⁴He ratio of 29 Ra, may have been involved in the origin of magmatism of Gorgona. Combining this with halogen compositions (Br/Cl and I/Cl ratios), which are similar to the mantle values, volatiles in the Gorgona komatiites and/or picrites would be derived from a less-degassed reservoir in the deep mantle, possibly in the core-mantle boundary.