Newry Igneous Complex, Late Palaeozoic intrusives, Northern Ireland

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Mitchell, W I (ed.). 2004. The geology of Northern Ireland-our natural foundation. Geological Survey of Northern Ireland, Belfast.

Introduction

A number of dates of intrusion have been published for the Newry Igneous Complex. While the oldest part of the Complex, the ultramafic-intermediate complex at Slievegarran gives an age of 403±3Ma, the southwestern pluton is dated at 399±21Ma based on whole-rock Rb-Sr isotope analysis [1]. A granodiorite from the margin of the northeast pluton gives a Rb-Sr age of 399±3Ma [2].

In the mid-20th Century the origin of the Newry Igneous Complex was controversial and ranged from a magmatic origin [3] to an essentially non-magmatic ‘transformist’ model involving large-scale, in situ metasomatism of the Silurian country rocks [4]. However, field, petrographic and geochemical evidence supports a magmatic origin for the complex. It is believed that the ultramafic rocks, and associated meladiorites originated by fractionation of intermediate magma of upper mantle origin. The layered nature of these rocks is probably the result of crystal accumulation in the magma chamber [5], [6]. Thus the three granodiorite plutons, which form the bulk of the complex, represent a more evolved melt that may have resulted from this process operating on a larger scale at deeper crustal levels.

The ultramafic-intermediate complex
The granodiorite plutons
Lamprophyre intrusions

References

  1. O’Connor, P J. 1975. Rb-Sr whole-rock isochron for the Newry granodiorite, NE Ireland. Scientific Proceedings of the Royal Dublin Society, A5, 407–13.
  2. Meighan, I G, and Neeson, J C. 1979. The Newry igneous complex, County Down. In: Harris, A L, Holland, C H, and Leake, B E (eds.). The Caledonides of the British Isles–reviewed. Special Publication of the Geological Society of London, 8, 717–22.
  3. Richey, J E, and Thomas, H H. 1932. The Tertiary ring complex of Slieve Gullion (Ireland). Quarterly Journal of the Geological Society of London, 88, 776–847.
  4. Reynolds, D L. 1944. The south-western end of the Newry igneous complex. A contribution towards the petrogenesis of the granodiorites. Quarterly Journal of the Geological Society of London, 99, 205–40.
  5. Meighan, I G, and Neeson, J C. 1979. The Newry igneous complex, County Down. In: Harris, A L, Holland, C H, and Leake, B E (eds.). The Caledonides of the British Isles–reviewed. Special Publication of the Geological Society of London, 8, 717–22.
  6. Reynolds, D L. 1944. The south-western end of the Newry igneous complex. A contribution towards the petrogenesis of the granodiorites. Quarterly Journal of the Geological Society of London, 99, 205–40.