A magnetic deep structural geology interpretation of Ireland

A new 10 nT compilation of magnetic data for Ireland and the immediately adjacent sea area shows distinct geophysical provinces of characteristic magnetic signature separated by major magnetic linears which can be related to important geological lines. In the far northwest there is a structurally coherent Grampian tectonic‐thermal zone bounded to the southeast by the Fair Head‐Clew Bay Line. Between the Fair Head‐Clew Bay Line and the western extension of the Southern Uplands Line, which forms the northern margin to the Southern Uplands of Scotland, is a segmented zone of relatively small magnetic anomalies and geological bodies of mixed crustal affinity: Grampian massifs, Lower Palaeozoic sedimentary basins bounded by major shear faults, relics of Lower Palaeozoic oceanic and related crust, and possible older microcontinent fragments. These separate areas have quite individual structural and metamorphic histories. There is good evidence for the Grampian Massifs having undergone significant lateral movement during Lower Palaeozoic times, and it can be inferred that many of the now adjacent bodies are only docked. The original position of each block is now not known. In the far southeast of Ireland are relics of a Cadomian Craton which are now tectonically imbricated with Lower Palaeozoic rocks. This is probably the segmented margin of the stable Cadomian craton which is inferred beneath Wales and south Britain. Between the Southern Uplands Line and the northernmost extent of the relics of the southern craton is a zone of deep‐seated, low‐amplitude magnetic anomalies and major linears. These are about 30° oblique to the southern margin of this vestiges of the Iapetus ocean zone, but are nearly parallel with the northern margin.