Extensional faults that localize Irish syndiagenetic Zn-Pb Deposits and their reactivation during Variscan compression

Abstract

Abstract The syndiagenetic Zn-Pb deposits of south-central Ireland, which are hosted by Lower Carboniferous carbonate sediments, occur along generally northeast trending, segmented normal fault arrays which were active during sedimentation. Individual sulphide bodies are located at points of maximum throw on east-west trending faults within the northeast trending fault arrays. All of the known major Irish Zn-Pb deposits in the south-central Midlands occur on north-side-down normal faults. The Irish Midlands underwent compressive shortening during the Variscan phase of the Hercynian orogeny. North-side-down normal faults were largely unaffected by this event while favourably oriented, south-side-down, Early Carboniferous normal faults were reactivated and transformed into reverse faults. The absence of significant sulphide deposits along south-side-down Chadian-Arundian extensional faults is probably due mainly to dismemberment, and/or compressional uplift and erosion, of such zones during Variscan deformation.