Melt Production in the Mantle: Constraints from U-series

U-series decay chains provide novel insights into mantle melting processes, notably on melting rates and on the porosity at which magma can separate from melting solid and the depth of melting. We review how such physical information can be derived from these geochemical measurements. U-series analyses are most clearly interpreted in the products of decompression melting, the most common mechanism of melting but also provide useful constraints on other modes of mantle melting such as isobaric heating and flux melting. There is tantalizing potential for U-series to constrain key aspects of mantle dynamics. The fraction of melt retained in the mantle informs on and influences its physical properties and U-series analyses clearly show that the residual melt porosity is ubiquitously low, only a few parts per thousand. Determination of melting rates from U-series measurements provides information about mantle upwelling velocities and mantle lithologies. This approach is of particular appeal in trying to understanding mantle plumes, although such scenarios are still under-constrained.