Palaeocene faulting in SE Sweden from U–Pb dating of slickenfibre calcite

Estimating the timing of faulting is crucial to modelling tectonics, palaeoseismicity, landscape evolution and fault mechanics. Four slickenfibre calcite samples from a conjugate strike‐slip fault set in a platformal limestone, SE Sweden, were dated using U–Pb. Three of the samples yielded an average age of 64.8 ± 6.5 Ma, while the fourth yielded a marginally younger age of 54.7 ± 5.5 Ma. Precipitation of the fibres is interpreted as syn‐deformational. Age uncertainty and dispersion reflect incorporation of common Pb and tiny host‐rock components into the dated calcite and/or possible fault reactivation through ca. 55 Ma. We infer from crystal characteristics, stable isotopes (δ¹⁸O and δ¹³C) and rare‐earth elements that fibres formed in an environment rich in deep‐seated fluids, at temperatures of 40–200°C, with shear stresses exceeding 10 MPa and at a maximum burial depth of c. 4 km. This Palaeocene faulting may reflect far‐field stresses from shortening in the Alps.