Abstract
CO 2 abundance and carbon isotope data are reported for basalt glasses from three spreading centres in the Central Lau Basin. Abundances of CO 2 dissolved in glasses vary from 9 ppm to 217 ppm with δ 13C ranging from −16.4‰ to −8.8‰. Evolved ferrobasalts from the propagating rift tip of the Central Lau Spreading Centre have both the lowest CO 2 concentrations and δ 13C values, while more magnesian basalts from the Intermediate and Eastern Lau Spreading Centres have higher CO 2 abundances with higher and less variable δ 13C values. Variations in abundance and carbon isotope ratios of dissolved CO 2 can be modelled by degassing during eruption of melts originally containing 410–440 ppm CO 2, with δ 13C of −7.7‰, using a vapour-melt isotope fractionation of 2.3‰. The type of degassing experienced by melts is related to their style of eruption, which is, in turn, governed by their eruption site. Central Lau Basin glasses, along with glasses from other marginal basins, display carbon isotope ratios which are lower than MORB. While the variations within the suite are adequately described by various degrees of degassing, carbon isotope heterogeneity between sources of oceanic basalts can not be discounted.
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