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Earth Science Conservation Review
| Ballyhalbert Pier | Down |
| Site number: | 579 | ||
| ESCC: | EF | ||
| Locality Type: | Coastal exposure | Status: | ASSI |
| Grid Reference: | J660633 Centroid | ||
| Google maps: | 54.49139,-5.4381 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Devonian, Silurian | ||
| Stages: | Lower Devonian | ||
| Lithostrat: | Newry Igneous Complex | ||
| Site Description | |
|---|---|
| Highlights: | |
This site comprises coastal exposure in which relationships between Silurian country rocks and undeformed lamprophyre dykes of the younger or uncrushed series of Reynolds (1931) can be seen. These Caledonian dykes were supposedly emplaced post-tectonically and are believed to be associated with the nearby Newry Igneous Complex. | |
| Introduction: | |
This site is located immediately east of Ballyhalbert Pier on the Ards Peninsula. Viewing of the exposure is tide dependent and should be done at least two hours before high tide on a rising tide, and one hour after high tide on a falling tide. Care is needed when traversing slippery rock surfaces. The first edition of the one-inch to the mile geological map Sheet 38 (Geological Survey of Ireland, 1869) shows a number of lamprophyre dykes of hornblende and mica type, intruded into folded Upper Silurian country rocks. In the accompanying explanatory memoir, Hull, Warren and Leonard (1871) described the country rocks and lamprophyre dykes in some detail. Reynolds (1931) made a number of significant advances in the study of the lamprophyre dykes. She described these dykes as uncrushed and assigned them to a "younger series" found to occur north of a line joining Ringburr Point on the west of the Ards Peninsula to Ringboy Point on the east. Current classification (Smith, Johnston and Legg, 1991) of these undeformed dykes indicates lamprophyres belonging to the vogesite and minette groups with occasional spessartites. | |
| Description: | |
The Silurian country rocks are of sedimentary origin and consist of interbedded greywacke sandstones and shales of turbiditic origin. Bedding is steeply inclined to the northwest and strikes northeast-southwest. At this location, two types of undeformed lamprophyre dykes occur; they are easily distinguishable from each other and from the country rocks. An earlier set of undeformed dark greyish green dykes, generally <1m thick, are almost bedding parallel. These dykes have a honeycombed surface caused by weathering out of phenocrysts. In places the dykes can be seen to terminate within the country rock. In thin section this is a porphyritic dyke rock composed mainly of hornblende pseudomorphs (10%) and plagioclase (10%) in a fine-grained groundmass (80%) composed of plagioclase, biotite and titanaugite (Merriman & Hards 2000). Although all of the primary minerals are altered, their nature and proportions indicate that this a variety of lamprophyre known as camptonite. Former hornblende phenocrysts (<1.5mm) are completely replaced by chlorite, carbonate and white mica, whereas plagioclase phenocrysts (<1.0mm) are replaced by carbonate and white mica. The groundmass consists of biotite, plagioclase laths and titanaugite, and in places shows a crude alignment caused by magma flowage. The most prominent intrusion at this site is an orange brown dyke that is ~2.5m wide and is almost bedding parallel. A ~1m wide offshoot of this dyke cuts across the earlier dykes (described previous paragraph) and so indicates the relative timing of intrusion events. In thin section this is a microporphyritic dyke rock which is composed mainly of hornblende (10%) and plagioclase (5%) in a fine-grained groundmass (65%) (Merriman and Hards, 2000). Although all of the primary minerals are altered, their nature and proportions indicate that this is dyke is also a camptonite. | |
| Importance: | |
Lamprophyre dykes of the younger "uncrushed series" of Reynolds (1931) can be viewed at the Ballyhalbert Pier site. The dykes form an important part of the geological history of the Caledonian mountain building event. | |
| Interpretation: | |
The relationship between folded Silurian country rocks and these undeformed lamprophyre dykes leads to the conclusion that the dykes were emplaced post-tectonically. More than one phase of intrusion is evident from the cross cutting relationships seen at this site. It is thought that the dykes are associated with the nearby Newry Igneous Complex. | |
| Conclusions: | |
Ballyhalbert pier is a high quality site where lamprophyre dykes of the younger or uncrushed series of Reynolds (1931) can be viewed. The dykes are interpreted as being emplaced at a time of low strain during the Caledonian Orogeny. The dykes are thought to be associated with the nearby Newry Igneous Complex and form an important part of the geological history of the mountain building event. | |
| 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 570 - Shannaghan Hill 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 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: | Greywacke, Shale, Turbidite, Lamprophyre, Minette, Spessartite, Vogesite |
| Structures: | Caledonian, dyke |
| Relations: | Intrusion |
| Access | |
|---|---|
| Management: | |
Given the limited exposure of these particularly useful examples of undeformed lamprophyre dykes, hammering or sampling should be restricted at this site. | |
| Threats: | Hammering and sampling should be restricted at this site. |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1869. 1:63,360 Geological Sheet 38. Dublin, Ordnance Survey for Geological Survey of Ireland. GEOLOGICAL SURVEY OF NORTHERN IRELAND, 1997. Northern Ireland. Solid Geology (2nd edition). 1:250,000. (Keyworth, Nottingham: British Geological Survey). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 04 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Ballyhalbert Pier, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=579. Accessed on 2026-11-05. |
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