Aughnavallog ASSI

Protected area type: Areas of Special Scientific Interest
Feature type: 
  • Earth Science
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Council: Armagh, Banbridge and Craigavon
Guidance and literature: Aughnavallog ASSI

Aughnavallog is a special place because of its earth science interest.  The area provides access to exposures of a granite-like rock called granodiorite that together with a number of other sites 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 ‘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 45km2from Slieve Croob in the northeast to Forkhill in south Armagh.  

The rocks at Aughnavallog form part of the northeast pluton and are of great importance as they give an indication as to where in the pluton they formed.  

At Aughnavallog the minerals that make up the granodiorite are randomly orientated.  This indicates that they formed well away from the contact with the surrounding ‘host’ rock.  If this was the case, then the minerals would be aligned, giving an almost stripy appearance as the hot magma was pushed against the edge of the pluton.  However, there is no such alignment at Aughnavallog indicating that the rocks formed at the centre of the pluton.  

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