IGNEOUS EMPLACEMENT IN A TRANSPRESSIVE SHEAR ZONE - OX MOUNTAINS IGNEOUS COMPLEX

The central and southwestern Ox Mountains Inlier in western Ireland, comprises amphibolite facies metasediments and metavolcanic rocks which have been deformed by a major sinistral shear zone. Granitoid emplacement Occurred in two distinct styles in the Ox Mountains shear zone. The older pluton, the Ox Mountains granodiorite was emplaced syn-kinematically with respect to the main sinistral, transpressional events in its wall rocks. It was emplaced as a series of compositionally distinct sheets in the central part of the shear zone system thus suggesting the formation of transient, dilational sites occurred in response to the transpressive deformation. The younger, Lough Talt and Easky Lough adamellites were emplaced as individual intrusions in dilational cavities produced by reactivated movements on a discrete zone within the Ox Mountains inlier. The different intrusive styles are considered to be a product of the tectonic regimes operating during emplacement. Intrusion into transient dilational cavities may be one method by which granitoid magmas are emplaced into fault zones undergoing active contractional deformation.