Late Caledonian sinistral strike-slip displacement across the Leannan Fault System, northwest Ireland

The Leannan Fault of north-west Ireland is a sinistral strike-slip fault system which juxtaposes Dalradian metasediments of differing structural trends and metamorphic grades. It probably represents a south-west splay of the Great Glen Fault of Scotland. The recognition and tracing of the Foyle Synform across the fault zone, together with the correlation of regional Dalradian strike swings, lateral sedimentary facies variation and metamorphic grades, suggest a sinistral displacement of 34 km across the fault. Members of the Leannan Fault system displace a Lower Devonian (about 397 Ma) granite, but are overlain by Visean (about 352 Ma) sandstones, thus constraining major late Caledonian sinistral motions to the Middle to Upper Devonian.