Camlough Quarry
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Geology & landscape
Geological Feature: Geological Fault, Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Paleogene, Silurian · Rock Type: Granite
Landscape processes: Volcanic / Igneous
Description
Camlough Quarry Caledonian igneous, Tertiary igneous The area is of special scientific interest because of its geology, which is seen in outcrop at a disused quarry on the west side of Camlough Mountain. The Slieve Gullion volcanic complex, of which Camlough Quarry is a part, is the finest example of a Palaeogene igneous centre in Ireland and is among the best topographic expressions of a ring-dyke system in the British Isles. The rocks found here are of international geological importance, having played an important role in a number of theories related to the development of and interaction between igneous rocks. The Slieve Gullion complex developed in an area of crustal weakness, previously exploited by the much older Newry granite, around 400 million years ago. In Palaeogene times, some 56-58 million years ago, it was the site of a major volcano of which there is now little evidence. Subsidence of this central unit was related to a ring fault, some 20 km in diameter, the latter providing a natural weakness exploited by intrusive igneous rocks. This produced the ring-dyke complex which has been exposed, through erosion of the softer surrounding rocks, to reveal the near-circular system known as the Ring of Gullion. The final phase saw activity return to the central area with apparently layered igneous rocks, both acid and basic in nature. Past debate on the formation of the central complex has been largely resolved. The layered structure apparent today appears to have developed as a series of igneous units intruded or injected into pre-existing rocks, rather than building up as a succession of extruded rock bodies. The Slieve Gullion complex is historically important as it has featured in a number of major geological debates on the nature of igneous rocks and the processes by which they can be formed. Camlough Quarry exposes the older country rocks which are the turbidites of Silurian age here melted and fused by the intrusion of the Newry granodiorite and altered into a hornfels and the late Caledonian age Newry granodiorite itself. The site contains evidence of the complex relationships between highly deformed sheared contact metamorphosed Silurian rocks and the Newry Igneous Complex. The quarry face also exposes the inner wall of the younger Palaeogene age ring dyke here consisting of a porphyritic granophyre. The intrusion is partially fault controlled, thereby providing evidence in support of the theory that the Slieve Gullion Ring Dyke was emplaced in a ring fracture generated during Palaeogene deformation. A late phase of movement along the fault has produced both crush-banded rocks known as mylonites and shattered angular rocks known as the Camlough Breccias. This location provides a fuller understanding of the geological history of the Slieve Gullion Ring complex. https://www.daera-ni.gov.uk/publications/camlough-quarry-assi