Abstract

Textural evidence is interpreted to suggest that in regions where upwelling rates of the mantle are slow to very slow, a small amount (∼2%) of melt was present when plagioclase-free abyssal peridotites entered the conductive regime at the base of the oceanic lithosphere. Upon crystallization, this melt appears to have been undersaturated in orthopyroxene, but precipitated clinopyroxene, Al-rich and Ti-poor spinel, and sulfides. Furthermore, the primary clinopyroxene grains have rare earth element patterns typical of residues of fractional melting, suggesting that the interstitial liquids were incremental partial melts rather than having mid-oceanic-ridge basalt compositions.

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