Tonalite bodies and basement-cover relationships in the North-eastern Ox Mountains Inlier, north-western Ireland

Detailed mapping in the Slishwood Division of the North-eastern Ox Mountains Inlier, north-western Ireland, has revealed two previously undescribed tonalite intrusions and an interleaved slice of Dalradian rocks. One tonalite, named the Kilroosk Tonalite, is poorly exposed at a single locality in the north-eastern part of inlier. The other tonalite, named the Giant’s Rock Tonalite, is a 10km-long, c. 50m-thick sheet-like intrusion, exposed in the south-western part of the inlier. It cuts granulite-facies fabrics within the Slishwood Division. Both the Giant’s Rock and Kilroosk intrusions were deformed during the Grampian Orogeny. The deformation affecting the Giant’s Rock Tonalite intensifies westwards, where the tonalite outcrop runs parallel to a 7km-long, c. 50m-thick slice of Dalradian cover that has been interleaved within the Slishwood Division basement. Interleaving of the cover and basement was apparently caused by east-south-easterly verging, shearing and folding. Later extensional deformation, allowing exhumation, has transposed earlier compressional fabrics in many areas.