Thermal modelling suggests that the problems posed by the high liquid temperatures (∼1,650 °C) of peridotitic lavas in Archaean greenstone belts, and the implied high degree of mantle melting (∼70%), are significantly reduced by considering uprise of a more refractory mantle diapir having an inherent density contrast with the surrounding mantle, and in a tectonic environment analogous to a marginal basin.