Abstract - Previous studies of post-Caledonian faults in Connemara argue for a significant phase of Tertiary normal faulting to explain the present day terrain and the offset geometry of the base Carboniferous unconformity. The latter indicates a series of ENE-E striking faults with vertical displacements ranging up to 850m. Here we review existing constraints and present new data on the geometry and timing of these faults. We suggest that the most parsimonious interpretation of the available data is that these faults are of Dinantian age, although some minor Tertiary reactivation cannot be ruled out. The main lines of evidence are: (i) The geometry and scale of these normal faults is comparable with those of Dinantian faults (i.e. those with associated syn-depositional effects and Zn-Pb mineralisation). (ii) Tertiary faults of similar scale or orientation are not seen in seismic datasets from offshore West of Ireland. (iii) There is no evidence for displacement of other Tertiary structures (e.g. dykes). (iv) Differential erosion of sequences across ‘dead’ faults provides ‘resequent fault scarps’ (e.g. in Western USA and northern England). We suggest that the difference in response to erosion of Carboniferous sediments and underlying basement could generate the present-day terrain, with no requirement for Tertiary faulting.
Abstract of poster presented at:
Irish Geological Research Meeting, Queens University, Belfast, February 2003