The Slishwood Division and Its relationship with the Dalradian rocks of the Ox Mountains

The Slishwood Division of northwestern Ireland is located along the southwestern margin of the Laurentian palaeocontinent. As detailed elsewhere in this guide (e.g., Chapters “The Basement and Dalradian Rocks of the North Mayo Inlier” and “The Central Ox Mountains”), the metamorphism and deformation of this region is generally attributed to the collision of outboard magmatic arcs with the Laurentian continental margin during the c. 470 Ma Grampian Orogeny. The Slishwood Division exhibits several features that are unique within the Grampian orogen. In particular, the metamorphic history of these rocks—early eclogite-facies and later high-pressure-granulite-facies—is different from that in any other region of the Grampian belt in Ireland or Britain. The Slishwood Division is plausibly explained as an exotic terrane that experienced at least part of its tectonic history in an outboard position, originating as a microcontinent rifted from Laurentia that experienced deep tectonic burial and arc magmatism before colliding with the Laurentian margin during the Grampian Orogeny. This chapter provides a series of field locations from which the evidence supporting this model was obtained, including evidence for a tectonic suture, the North Ox Mountains Slide, along which a small remnant ophiolitic fragment may be examined.