Abstract

Dr M. L. F. Bamford writes: Cooper et al. 1986 described a thin-skinned model for the Irish Variscides. The sequence of events established was initial layer-parallel shortening followed by buckle folding and finally thrusting. They considered that this sequence of events moved progressively northwards developing above a sole thrust. Sanderson (1984) proposed a dextral transpression model for the Variscides based on field data from the western part of the fold belt. Whilst Cooper et al. 1986 accepted that a component of dextral strike-parallel shear occurred in the west, they argued that the north-south compressional component is more significant than transpression. These two models are not incompatible once the dextral transpression in the west is not considered to be thick skinned as favoured by Sanderson (1984).

Ford (1985) proposed that a surge zone (sensu Coward 1982) occurs in the centre of the fold belt. Towards the east this is accommodated by the predominance of dextral movement on north-south wrench faults and the swing of the fold axis from 070" in the centre of the fold belt to 110" in the east (Cooper et al. 1986). It has been suggested by Murphy (1985) that in the east, temporary sticking points on the sole thrust produced both the swing in fold axis orientation and the north-south dextral wrench faults (Fig. 1). In the western part of the fold belt the fold trend swings towards 055" and Murphy (1985) suggested that temporary sticking points may also have occurred. However, north-south wrench faults in the western