A model is proposed in which Pb is preferentially partitioned into the melt during partial melting of the mantle resulting in a higher U/Pb ratio in the residual mantle. The degree of increase is suggested to be inversely correlated with the degree of melting. By combining subduction of oceanic crust (&mgr;crust<&mgr;source) into the lower mantle with intra-crustal fractionation of U/Pb through magmatic and metamorphic differentiation, this model can explain the J-type Pb in both the upper mantle (i.e., young oceanic volcanics) and the upper continental crust. It obviates the need for an extended period of core formation or recycling of continental materials into the mantle to explain the J-type leads although it does not preclude the occurrence of either of these mechanisms.