Palaeocene faulting in <scp>SE</scp> Sweden from U–Pb dating of slickenfibre calcite

Abstract

Abstract 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 (δ 18 O and δ 13 C) 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 MP a and at a maximum burial depth of c. 4 km. This Palaeocene faulting may reflect far‐field stresses from shortening in the Alps.