Regional-scale melt-rock interaction in lherzolitic mantle in the Romanche Fracture Zone (Atlantic Ocean)

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 lherzolites are consistent with a relatively low upper mantle temperature below the Romanche region. Group 2 peridotites can be explained by reaction between melt and lherzolite, at a temperature close to the peridotite solidus, in a still upwelling upper mantle.