Post-tectonic clastic dykes in the Dalradian of Scotland and Ireland: implications for delayed lithification and deformation of sediments

Structures associated with soft-sediment deformation are preserved in the Neoproterozoic Dalradian Supergroup of SW Scotland and NW Ireland. Clastic dykes display a range of age relationships to regional Caledonian D-1 folds and fabrics from pre-tectonic to hitherto unrecognized post-tectonic. Evidence for the post-D-1 timing of some dykes includes the emplacement of centimetre-scale injections along regional S-1 cleavage, the disorientation and transport of cleaved wall-rock clasts within larger dykes, and elastic dykes which markedly cross-cut and transect F-1 fold hinges and axial planes. Collectively, these observations are compatible with the earliest regional (D-1) structures deforming a sequence which contained locally overpressured and unlithified pockets of sediment. These critical relationships indicate that over-pressured pockets of unlithified sediment were possibly retained within the Dalradian for significant periods of time spanning at least 120 Ma given existing isotopic constraints. Copyright (C) 2000 John Wiley & Sons, Ltd.