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

We report high-precision Ca-44/Ca-40 measurements (2 sigma m < 0.06 parts per thousand) of Hawaiian shield stage tholeiites. Our data reveal similar to 0.3 parts per thousand variation in their Ca-44/Ca-40, which comprises similar to 20% of the Ca-44/Ca-40 variation observed in global carbonates. The Ca-44/Ca-40 variation is correlated with Sr/Nb and Sr-87/Sr-86, 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. (C) 2011 Elsevier Ltd. All rights reserved.