The origins of the magnetic anomaly over the Lough Derg Complex, Co. Donegal, Ireland

Abstract

The ring-shaped negative magnetic anomaly over the psammites of the Lough Derg Complex, considered to be a part of the pre-Caledonian basement in Co. Donegal, is shown to be due to an extremely stable permanent magnetism. Although the rocks probably acquired their present magnetization during the Caledonian orogeny, the magnetic mineral itself, possibly an ilmenohaematite, could well be older. It seems possible that other negative anomalies in the region of low magnetic field between the Highland boundary and Great Glen Fault zones could be produced by a similar process.