Post-tectonic elastic 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 N eoproterozoic Dalradian Supergroup of SW Scotland and NW Ireland. Clastic d ykes display a range of age relationships to regional Caledonian D-1 folds and fabrics from pre-tectonic to hitherto unrecognized post-tectonic. Evide nce for the post-D-1 timing of some dykes includes the emplacement of centi metre-scale injections along regional S-1 cleavage, the disorientation and transport of cleaved wall-rock clasts within larger dykes, and elastic dyke s which markedly cross-cut and transect F-1 fold hinges and axial planes. C ollectively, 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 & Son s, Ltd.