Mantle-derived peridotites recovered from the Romanche Fracture Zone fall in two compositional groups. Group 1 nearly undepleted lherzolites, indicating a very low degree of melting, are prevalent in the western part of the transform. Group 2 peridotites, with higher Mg/Fe ratio but enriched in Ti and incompatible trace elements and generally containing plagioclase, are common in the eastern part of the transform, where undepleted samples are also present. Group 1 undepleted Iherzolites are consistent with a relatively low upper mantle temperature below the Romanche region. Group 2 peridotites can be explained by reaction between melt and Iherzolite, at a temperature close to the peridotite solidus, in a still upwelling upper mantle.
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