AbstractPegmatite dyke swarms are exposed within the easternmost Pyrenees at Cabo de Creus. These dykes were emplaced into high‐grade metamorphosed sedimentary strata of Cambro‐Ordovician age, but lack obvious field relationship to Hercynian intrusive rocks. Together with structural and geochemical data, equilibrium oxygen isotope fractionations at temperatures of ≈ 600°C, the lack of obvious subsolidus exchange, and the H‐ and O‐isotopic signatures of water in equilibrium with pegmatite mica and quartz are interpreted to indicate a derivation from anatexis of a metapelitic source at shallow crus