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Earth Science Conservation Review
| Shannaghan Hill | Down |
| Site number: | 570 | ||
| ESCC: | EO | ||
| Locality Type: | Inland exposure | Status: | ASSI |
| Grid Reference: | J21854070 Centroid | ||
| Google maps: | 54.30101,-6.12902 | ||
| County: | Down | Council area: | Armagh City, Banbridge & Craigavon Borough Council |
| Period: | Devonian, Silurian | ||
| Stages: | Lower Devonian | ||
| Lithostrat: | Newry Igneous Complex | ||
| Site Description | |
|---|---|
| Highlights: | |
A series of exposures on Shannaghan Hill demonstrate complex relationships between contact metamorphosed Silurian country rock, lamprophyre dykes and sheeted granodiorite of the northeast pluton of the late Caledonian Newry Igneous Complex. | |
| Introduction: | |
The site is located on the south-western slopes of Shannaghan Hill, approximately 1km east of Katesbridge. Access to the site is via a farm track joining the A50 (Banbridge to Castlewellan). Geologically, the site lies at the northern margin of the northeast pluton that forms part of the late Caledonian Newry Igneous Complex. The first edition of the one-inch to the mile geological map (Banbridge, Sheet 48) (Geological Survey of Ireland, 1871) indicates a zone of contact metamorphism, up to 1km wide, immediately west of the site. The contact between 'indurated' country rock and granite dips steeply to the northwest. The strike of the contact is close to parallel to that of the bedding in surrounding Silurian sediments. Bedding dip within the country rock is variable but generally steep (50° to 80°). There are two prominent directions of dip, towards the northwest and southeast, indicating folding. In the accompanying geological memoir, (Egan, 1872) observed that "fine-grained Granite appears extensively at the surface". Two 'felstone' dykes trending northwest to southeast are also described. The country rock is recorded as being "large masses of fine grit" retaining original dips and displaying the characteristics of fused (mobilized) sediment as described later by Reynolds (1934; 1936). Petrology and classification of the granite by Reynolds (1934; 1936) showed the rocks to be granodioritic. Reynolds' classification and terminology still stand with modern schemes (Streckeisen, 1976). Systematic sampling, thin section petrology and geochemistry (Neeson, unpublished; Grant, 1961; Meighan and Neeson, 1979) revealed that the granodiorite at the margins of the northeast and southwest plutons is more basic than granodiorite exposed towards the centres of the intrusions. This pattern of geochemical zoning has been described as "normal zoning". The opposite pattern is seen for the middle pluton, which is described as displaying "reverse zoning". Meighan & Neeson (1979) published Rb-Sr age of 399±3Ma for the granodiorites of the northeast pluton. Field relations indicate that this pluton was the first of the three major constituent bodies which together form most of the Newry Igneous Complex. | |
| Description: | |
Located on the south-western slopes of Shannaghan Hill, approximately 1km east of Katesbridge, a series of natural exposures demonstrate complex relationships between contact metamorphosed Silurian country rock, lamprophyre dykes and sheeted granodiorites of the northeast pluton of the Newry Igneous Complex. Metamorphosed country rocks exposed within the site are mainly biotite-hornfels and fused (mobilized) sediment. The strike and dip of bedding, despite numerous intrusions, is consistent with that seen in the country rock to the north. A complex association of lamprophyric dykes and granodiorite sheets can be observed. The lamprophyric dykes are found associated particularly with the northeast of the Newry Igneous Complex (Reynolds, 1931). Granodiorite that forms part of the northeast pluton is exposed as cross cutting, and in some cases partially remobilized, sheet-like intrusive bodies that show variable deformation. Foliation of minerals occurs within the granodiorite sheets and is a feature generally restricted to the margins of plutons within the Newry Igneous Complex (Reynolds, 1934; Meighan & Neeson 1979). | |
| Importance: | |
Shannaghan Hill is a site of national importance offering access to a series of exposures that demonstrate the complex relationships between contact metamorphosed Silurian country rock, lamprophyre dykes and sheeted granodiorites of the northeast pluton of the Newry Igneous Complex. The site demonstrates the complex early stages of intrusion of the northeast pluton and the interaction with lamprophyre dykes. Field evidence proves that there was an overlap between the time for the intrusions and the regional deformation. | |
| Interpretation: | |
At Shannaghan Hill, heat from the northeast granodiorite pluton of the Newry Igneous Complex has caused contact metamorphism of the Silurian greywacke and shale country rock. The resulting rock types are hornfels and fused (mobilized) sediment. Sediments have been mobilized, intruded by melt and recrystallized giving rise to the complex field relationships observed. The complex cross-cutting relationships between lamprophyre dykes and various granodiorite sheets indicates contemporaneous intrusion and regional deformation (Cameron, 1981). The granodioritic sheets are considered to represent the early stages of intrusion of the northern pluton of the Newry Igneous Complex. The presence of foliation within sheeted granodiorites in this area is attributed to regional deformation and shouldering aside of country rock during emplacement of the Newry Igneous Complex. Tectonic fabrics are aligned parallel to the main contact and lend weight to the diapiric intrusive model of formation proposed by Murphy (1987). | |
| Conclusions: | |
Shannaghan Hill is a site of national importance offering access to contact metamorphosed Silurian country rock, and granodiorite sheets which represent the early stages of intrusion of the northeast pluton. The interaction of lamprophyre dykes and granodiorite can also be demonstrated. Field evidence proves that there was an overlap in time for the intrusions and the influence of regional deformation and shouldering aside of country rock during emplacement of the Newry Igneous Complex. | |
| Notes: | |
For information and references on other sites within the Newry Igneous Complex see the following sites: Key Site 568 - Ardglass, Co Down Key Site 569 - Slieve Croob Key Site 571 - Ballymagreehan Quarry Key Site 572 - Rathfriland Key Site 573 - Gransha Key Site 574 - Aughnagon Quarry Key Site 575 - Goraghwood Quarry Key Site 576 - Newry By-pass Key Site 577 - Cam Lough Quarry Key Site 578 - Kearney Point Key Site 579 - Ballyhalbert Pier For general information and references on the Caledonian Igneous Complexes of N. Ireland, and for directions to other regional sites, see the following site: Key Site 595 - Introduction to the Caledonian Igneous Complexes of N. Ireland | |
| Keywords | |
|---|---|
| Rocks: | Granodiorite, Greywacke, Hornfels, Shale, Lamprophyre |
| Structures: | Caledonian, dyke, pluton, mobilisation |
| Relations: | Intrusion, Contact metamorphism |
| Access | |
|---|---|
| Approach: | Access to the site is via a farm track joining the A50 (Banbridge to Castlewellan). |
| Management: | |
This site occupies an area of partially fenced farmland currently used for rough grazing of sheep. Access is via a farm track that joins the A50 between Banbridge and Castlewellan. Landowner permission should sought before entering this land. Despite the abundance of outcrop within this site, it would be wise to restrict hammering or sampling as important small-scale features could quickly be degraded or destroyed. The rocks of the Newry Igneous complex are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration and production has previously been carried out in Counties Armagh and Down. The area which includes this site is likely to attract further exploration activity. | |
| Threats: | Possibly sensitive to over-sampling. |
| Uses | |
| Uses: | Farmland |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1871. 1:63,360 Geological Sheet 48 (Banbridge). (Dublin, Ordnance Survey for Geological Survey of Ireland). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 03 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Shannaghan Hill, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=570. Accessed on 2026-11-08. |
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