MAGNETIC CRUSTAL CHARACTER IN CENTRAL IRELAND

The simplest magnetic model for the upper 20 km of crust in central Ir eland is of two layers. A thin, weakly magnetic upper layer carrying a number of magnetic bodies that can be related to surface geology over lies a magnetic crustal zone whose gross magnetization increases towar ds the north. The deeper trace of the Iapetus Suture in central Irelan d forms the boundary between a more magnetic northern crustal area and a less magnetic southern area. A pre-Carboniferous major dextral offs et of this suture boundary occurs in the Limerick area. The suture is traced beneath the Dingle peninsula in the far south-west of Ireland. In east-central Ireland, between the Iapetus Suture and Southern Uplan d Line, the crust contains a large, south-dipping magnetic body with n o surface expression, which produces the Virginia magnetic anomaly. Th e development of magnetic bodies - in particular, volcanic rocks of Ca rboniferous age - has been controlled by regional stress patterns. The major volcanic centre at Limerick lies at the intersection of two maj or Caledonian block fault systems just to the north of the surface tra ce of the Hercynian Front.