1. THE STRUCTURAL FRAMEWORK OF NORTHERN IRELAND
1.1 PLATE TECTONICS
The development and general acceptance of plate tectonic theory, in particular the key mechanism of continental drift, has provided geologists with a mechanism to account for the worlds major structural and metamorphic terranes and the discontinuities that exist between adjacent terranes. North of the Iapetus suture a number of terranes, which now make up northern Britain and Ireland, formed at sites along the Laurentian (North American) continental margin in the Iapetus Ocean. These terranes were brought together into their present configuration as a result of large-scale sinistral transpressive movements.
1.2 TERRANES
The rocks in Northern Ireland range in age from the early Proterozoic (Moinian) to Recent. The older and often structurally complex rocks (Early Proterozoic to Lower Palaeozoic) have been divided into a number of distinct tectono-stratigraphic ‘terranes' which are separated by major NE-SW trending bounding faults (Fig. 1, after Bluck et al., 1992). Each terrane consists of rocks of similar geological provenance and a shared metamorphic and deformational history. These terranes coalesced or ‘docked' in their present juxtapositions as a result of oblique compressional earth movements during late-Caledonian times. The nomenclature for the principal terranes and terrane boundaries in Northern Britain is derived mainly from the classic regions of Scottish geology where much of the pioneering research into structural geology was carried out. This nomenclature has been extended, and applied, with a few minor modifications, to Northern Ireland.