Abstract During the Carboniferous, Northern Ireland straddled a zone of dextral strike-slip faulting, comparable to the Midland Valley of Scotland (see Chapter 14). The earliest Mississippian marine transgression reached Northern Ireland in the late Tournaisian (CM Miospore Biozone) and from then until the mid-Arnsbergian Substage (E 2b 1 Subzone) the sediment fill was deposited in close proximity to the northern margin of the basin. Metamorphic rocks of the Central Highlands (Grampian) Terrane to the north were repeatedly exposed during episodes of marine regression. In the SE of the region it appears that the Southern Uplands-Down-Longford Terrane was finally submerged in the late Asbian or early Brigantian. The cumulative thickness of 7000 m is represented mainly by Tournaisian, Visean and lower Namurian rocks in Co. Fermanagh, the Fintona Block, peripheral sections at Coalisland and isolated basins such as Newtownstewart, all in Co. Tyrone (Fig. 51). The most continuous outcrop and succession extend from Co. Fermanagh and south Co. Tyrone into north Co. Armagh. The Carboniferous outcrop in the eastern part of Northern Ireland is reduced to outliers at Ballycastle in Co. Antrim, and in Co. Down at Cultra, Castle Espie and Carlingford Lough. During the Pennsylvanian, much of Northern Ireland was land, and strata of this age are limited in extent to the Fintona Block and east Co. Tyrone (Fig. 51).

Abstract The northeast Ox Mountains inlier forms an ENE-trending, 40km long, narrow, arcuate ridge of bare, psammitic hills which passes to the southeast of the town of Sligo in northwest Ireland. (It lies to the northeast of the area of Fig. 16 shown on Fig. 13 and ornamented tentatively as Grampian Group in Chapter 4). It is surrounded by Lower Carboniferous sediments except at its western end where a poorly exposed fault, the Ladies Brae fault, brings it against pelitic rocks of inferred Dalradian age in the central Ox Mountains inlier (Lemon 1971; Phillips et al . 1975; Chapter 4, this volume). Lithologically the inlier comprises migmatitic psammites, minor pelites and rare marbles, with locally important early ultrabasite, metabasite and metagranitoid bodies, and late granite pegmatites. A stratigraphical succession has not been established; Lemon’s (1971) map shows undifferentiated ‘Moine feldspathic granulites’, although Pyne (1972) mapped three formations, a pelite sandwiched between two psammitic units, to the west of Collooney.

Abstract The South Central Ireland region extends from the South Munster Basin north to the southern margin of the Dublin Basin and from Wexford in the SE to the Burren in the NW (Fig. 59). The region is dominated by strata of Mississippian age, with Pennsylvanian strata preserved in boreholes in south Co. Wexford and in the upper part of the Leinster and Kanturk coalfields. Throughout the South Central region, the Tournaisian strata present below the Waulsortian mud-bank limestones, which form a continuous thick unit of massive pale grey limestone across most of the region, are represented by the Lower Limestone Shale and Ballysteen Limestone groups (Brück 1985) of the Limerick Province (see Philcox 1984; Sevastopulo & Wyse Jackson 2009). The Lower Limestone Shale Group is related to a northward-directed marine transgressive event across the North Munster shelf. The deepening trend, which started during the deposition of the Ballysteen Limestone Group, continued with the Waulsortian facies on the distal part of a ramp. From the latest Tournaisian time and throughout the Visean there is widespread development of shallow-water marine carbonate platform sediments with only localized deeper-water ramp and basinal facies (mostly in the Shannon Basin) (Somerville et al. 1992b; Strogen et al. 1996; Sevastopulo & Wyse Jackson 2009). The greatest areal extent and stratigraphic thickness (c. 2 km) of Namurian rocks occurs in the Shannon Basin, centred on counties Clare and Limerick.

Abstract The Caledonides of Britain and Ireland are one of the most intensively studied orogenic belts in the world. This review considers all the tectonic events associated with the development and closure of the Iapetus Ocean. It first summarizes the tectonic evolution of each segment involved in the Scottish–Irish sector of the Caledonides and then reviews the temporal evolution of the Caledonian Orogeny. Three main tectonic phases are recognized in the Scottish–Irish Caledonides: an Early–Middle Ordovician (475–465 Ma) phase termed the Grampian Orogeny; a phase of Silurian (435–425 Ma) tectonism restricted to the Northern Highland Terrane of Scotland termed the Scandian Orogeny; and an Early Devonian (395 Ma) phase termed the Acadian Orogeny. The Grampian Orogeny was caused by the collision of the Laurentian continental margin with an oceanic arc terrane and associated suprasubduction zone ophiolites during the latest Cambrian–Early Ordovician. Following the Grampian arc–continent collision event, there was a subduction polarity reversal. This facilitated continued subduction of Iapetan oceanic lithosphere and an Andean-type continental margin developed on and adjacent to the Laurentian margin in the Middle Ordovician along with a substantial thickness of accretionary prism sediments (the Southern Uplands–Longford Down Terrane). The Iapetus Ocean is believed to have disappeared by the Late Silurian based on the faunal record and a continent–continent collision ensued. The absence of significant regional deformation and metamorphism associated with the Late Silurian collision between Avalonia and the Scottish–Irish margin of Laurentia suggests that the continental collision in this sector of the Caledonian–Appalachian orogen was ‘soft’ or highly oblique. The exception is the Northern Highlands Terrane of Scotland that was believed to have been situated 500–700 km to the north along orogenic strike. This terrane records evidence for significant Silurian regional deformation and metamorphism attributed to the collision of the Laurentian margin of East Greenland with Baltica (the Scandian Orogeny). Current controversies in the Laurentian Caledonides of Scotland and Ireland are discussed at the end of this review.

Abstract In Scotland and Ireland, a Laurentian passive margin sequence, the Dalradian Supergroup, was deformed during the c. 470–460 Ma Grampian orogeny, resulting in the formation of crustal-scale recumbent nappes. In Ireland, this passive margin sequence is in general bounded to the SE by the Fair Head–Clew Bay Line (FHCBL), a segment of a major lineament within the Caledonides. Adjacent to the FHCBL, Dalradian metasediments in two separate inliers have undergone post-Grampian strike–slip movement, with the initially flat-lying Grampian nappe fabric acting as a décollement-like slip surface in both cases. As the orientation of these foliation slip surfaces was oblique to the local shear plane in both inliers, displacement along these pre-existing foliation surfaces was also accompanied by crenulation slip. However, the crenulation-slip morphologies produced imply the opposite sense of movement in the two inliers. 40 Ar− 39 Ar dating of muscovite defining the crenulation-slip surfaces indicates that post-Grampian dextral displacement took place along the FHCBL at 448 ± 3 Ma. A subsequent phase of sinistral movement along the FHCBL took place at c. 400 Ma, based on previously published Rb–Sr muscovite ages for synkinematic pegmatites. The kinematic information obtained from crenulationslip morphologies combined with geochronology can thus be used to constrain the reactivation history of a major crustal-scale shear zone.