U–Pb isotopie data for zircons from a granulite-facies xenolith from a volcanic vent at Partan Craig in the southeastern part of the Midland Valley of Scotland display evidence of an early Proterozoic (>2·0 Ga) component. The xenolith is probably relict metasediment and the data therefore indicate old detritus in the sedimentary precursor. The exact ages of sedimentation and metamorphism are uncertain but these must be compatible with Sm–Nd data on similar xenolithic fragments from the same locality which constrain the ages to c. 1–0 Ga or younger.
