Discussion of a model for the development of the Irish Variscides

Abstract

E. A. Williams, M. Ford & H. E. Edwards write: Price & Todd (1988) present a model for the development of the Irish Variscides which suggests that ‘an array of superjacent normal faults’ supposedly constituting the extensional framework of the Munster Basin, was re-used during Variscan transpression to produce the Variscan fold and thrust belt in southern Ireland. Whilst there is no controversy regarding the generality of Variscan inversion of at least one late Palaeozoic half-graben in southern Ireland, we are unable to agree with Price & Todd over their concepts of the extensional basinal setting or indeed those of the macroscopic structural geology of the Irish Variscides. Price & Todd use the latter to infer numerous originally extensional basin-forming faults, without attempting to substantiate such structures with critical data such as sedimentary thickness, facies and stratigraphical contrasts. Moreover, they stress regional Variscan dextral transpression when most of the evidence ( Collins 1985 ; Trayner 1985 ; Cooper et al. 1986 ; Ford 1987 ; authors' unpubl. data) points to compressional deformation. For clarity, these points are dealt with under headings comparable to those used by Price & Todd in their paper, although not in the same order. Northern margin of the Munster Basin. The depiction by Price & Todd (1988, fig. 1a) of the Killarney-Mallow Fault as the northern margin of the Munster Basin, and the nature and location of the structures they show on the Iveragh Peninsula and elsewhere (fig. 1a, b) constitute our principal objections to their model. The Killarney-Mallow Fault is