| Site Type: | Inland exposure | | Site Status: | ASSI | | Council area: | Newry, Mourne & Down District Council | | Grid Reference: | J160354 | | Bing maps: | 54.25477,-6.22012 | | Google maps: | 54.25477,-6.22012 | | Rocks |
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| Rock Age: | Devonian, Silurian (Lower Devonian) | | Rock Name: | Newry Igneous Complex | | Rock Type: | Granodiorite | | Interest |
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| Other interest: | Caledonian, pluton, enclave, normal zoning, Intrusion |
| Summary of site: |
| This site provides access to exposures of a granite-like rock called granodiorite that, together with a number of other designated sites in the area collectively describe the Newry Igneous Complex. The granodiorite was formed some 410 million years ago. This is an igneous rock type, that is, it was injected as magma (molten rock) into pre-existing older rocks—Silurian sedimentary rocks. These older rocks are known as the ‘host’ rocks. The magma then cooled slowly eventually forming huge masses of solid rock deep beneath the surface. Subsequent erosion has now exposed parts of these enormous rock units. Each of these igneous rock units is referred to as a pluton. Three of these are present which collectively make up the Newry Igneous Complex. The Complex extends over an area of about 45km2 from Slieve Croob in the northeast to Forkhill in south Armagh. The rocks at Gransha form part of the northeast pluton and are of great importance as they give an indication as to where in the pluton they formed. These rocks form part of a wider geological story. Some 420 million years ago, a now lost ocean called the Iapetus Ocean, was shrinking as the continents on either side came together and eventually collided. The northern continent of Laurentia was formed of much of what is now North America, together with the north of Ireland and Scotland. The southern continent of Avalonia was made up of the south of Ireland, England and Wales. The older Silurian sedimentary rocks, which are very widespread in Co. Down, formed in this ocean. As the continents collided, an enormous mountain chain was formed. This is now mainly eroded away with remnant pieces forming the Scottish Highlands, the Sperrins and the uplands in Norway and Sweden. The rocks that make up the Newry Igneous Complex formed in association with major earth movements which followed this collision and period of mountain building. The heat generated as a result of this, produced huge volumes of magma deep within the Earth resulting in the formation of a number of igneous complexes, including the one at Newry. | | Unlike other locations, some of the minerals in the Gransha rocks are aligned, giving an almost stripy or ‘foliated’ appearance. The stripes are typically parallel to the contact between the granodiorite and the older host rocks. They formed as the hot magma was pushed against the host rock at the edge of the pluton. The granodiorite at Gransha also contains units or enclaves of other rock types. These can be either of sedimentary (Silurian sedimentary rocks) or igneous (older than the granodiorite) origin and can be clearly seen as patches of different coloured rocks within the granodiorite. These enclaves are typically found along the margins of the magma chambers. Both the foliation and the enclaves tell us that Gransha formed on the margins of the pluton. |
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