Ring of Gullion AONB 3.31

The Ring of Gullion is a geological formation and area, officially designated as an Area of Outstanding Natural Beauty, (AONB) located in County Armagh, Northern Ireland. The area centres on Slieve Gullion, the highest peak in County Armagh, measures roughly 42 by 18 kilometres (26 by 11 mi) and comprises some 150 km² defined topographically by the hills of an ancient ring dyke. Parts of the area have also been officially listed as Areas of Special Scientific Interest.The geological formation was the first ring dyke to be mapped, although its significance was not understood until similar structures had been described from Scotland. It was emplaced during the Paleogene opening of the Atlantic Ocean during the formation of the North Atlantic Igneous Province.Geological history and featuresThe structure of the ring dyke was produced when the active volcano's caldera underwent collapse producing a concentric suite of faults providing space into which magma was able to intrude. The ring dyke is composite with both porphyritic granophyre and porphyritic felsite components. The composition of the remainder of the volcano today is dominated by gabbro and granophyre and is also the site of a noted occurrence of platinum group elements.