Nd and Sr isotope evidence linking mid-ocean-ridge basalts and abyssal peridotites

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Peridotites found on the sea floor are widely believed to be residues left by mid-ocean-ridge basalt (MORE) melting. As such, their composition should provide insights into the nature of the sub-oceanic depleted mantle. But although these abyssal peridotites occur in mid-ocean ridge fracture zones 1,2, there is little other evidence in support of their genetic link with MORB, and doubts about it have been raised3-5. Radiogenic isotopes should be able to provide a powerful test of the hypothesis, but previous studies3,8-10 on whole rocks have not provided unambiguous answers as they are generally altered by sea water. Here we present measurements of the Nd and Sr isotope compositions of a suite of abyssal peridotite clinopyroxenes which should have resisted alteration. Despite residual seawater contamination of Sr in the clinopyroxenes, the data demonstrate that the peridotites are from a depleted mantle source, identical to that of MORB. This provides a strong indication that abyssal peridotites are residues of MORB melting. © 2002 Nature Publishing Group.

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