Stable calcium isotopic compositions of Hawaiian shield lavas: Evidence for recycling of ancient marine carbonates into the mantle

We report high-precision 44Ca/40Ca measurements (2σm < 0.06‰) of Hawaiian shield stage tholeiites. Our data reveal ∼0.3‰ variation in their 44Ca/40Ca, which comprises ∼20% of the 44Ca/40Ca variation observed in global carbonates. The 44Ca/40Ca variation is correlated with Sr/Nb and 87Sr/86Sr, and this pattern is best explained by adding up to 4% ancient carbonate into the Hawaiian plume. Mass-balance calculations show that up to 40% of the Ca budget and 65% of the Sr budget in some Hawaiian (Makapuu-stage Koolau) lavas are derived from recycled carbonates. Our finding demonstrates, for the first time with the application of Ca isotopes, that ancient recycled carbonates are important components of mantle plumes which feed some of the largest terrestrial volcanoes. Thus, recycling of carbonates into the mantle is an essential part of the global Ca and C cycles.