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Earth Science Conservation Review
| Craiganawork, Pomeroy | Tyrone |
| Site number: | 591 | ||
| ESCC: | EO | ||
| Locality Type: | Inland exposure | Status: | ESCR |
| Grid Reference: | H26773758 Centroid | ||
| Google maps: | 54.28608,-7.59001 | ||
| County: | Tyrone | Council area: | Fermanagh & Omagh District Council |
| Period: | Devonian, Ordovician | ||
| Lithostrat: | Old Red Sandstone, Pomeroy Granite, Tyrone Plutonic Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The Pomeroy Granite is one of a chain of four granitoid plutons aligned parallel to the dominant Caledonian strike in Counties Tyrone and Londonderry. The plutons resemble the Newer Granite plutons of Scotland and may have been intruded during a late stage of the Caledonian Orogeny. | |
| Introduction: | |
The Craiganawork site is located ~4km northwest of Pomeroy, County Tyrone. The first edition of the Ballygawley (Sheet 34) one-inch to the mile geological map (Geological Survey of Ireland, 1913 Edition) shows an intrusive granite body intruded into hornblendic and pyroxenic country rocks northwest of Pomeroy. The Sheet 34 memoir (Nolan, 1878) describes an extensive tract of granite, including that exposed around Beragh and Carrickmore. The granite was considered to be of Old Red Sandstone age; an age based on contact relationships and apparent thermal metamorphism. The second edition off Sheet 34 (renamed Pomeroy) represented the Pomeroy Granite as an elongate pluton aligned parallel to the dominant Caledonian strike (Geological Survey of Northern Ireland, 1979). The pluton was emplaced into gabbros and dolerites of the Tyrone Basic Plutonic Complex; a relationship demonstrated by the occurrence of a narrow thermal aureole. The Beragh and Carrickmore plutons are shown intruding into gneissose rocks of the Corvanaghan Formation. This relationship is shared by the Slieve Gallion intrusion which lies further to the northeast in south Londonderry. The summary of the geological history of the Pomeroy Sheet relates the Pomeroy pluton to the intrusions at Beragh and Carrickmore and suggests that the granites pre-date the Tyrone Volcanic Group (Ordovician). Although research on these granites is limited, the current belief is that these intrusions most closely resemble the younger Caledonian granites (late Ordovician or Silurian age). The contact relationship of the granite with Lower, Middle and Upper Devonian sequences that overly the granites, seems to support this younger Caledonian age for the suite. This is in contrast with the early Caledonian age proposed for the Craigballyharky tonalite (Key Site 590 - Craigballyharky and Craigbardahessiagh) and the porphyritic dacite at Cushendun (Key Site 594 - Cushendun). It should however be noted, that these granites are not seen to intrude Ordovician sediments so could be of a similar age to Craigballyharky tonalite. It is hoped that radiometric age dating studies of the Pomeroy Granite (work in progress) will shed light on the age and contact relationships of the granite. | |
| Description: | |
The Craiganawork site comprises an extensive area of natural exposure which can be accessed via farm tracks and fields from Murnells Road. The rock is a light pinkish very coarse-grained biotite-bearing granite. In hand specimen, the rock has conspicuous large alkali feldspar crystals and plagioclase with minor biotite. The large quartz grains can be seen to join to form ribbons that define a fabric. This fabric has typically Caledonian northeast to southwest trend across the entire site and dips steeply to the north and the boundary of the pluton. In thin section, the proportions of the main mineral constituents granite are as follows: highly strained quartz (35%), alkali feldspar (35%), plagioclase (25%) and biotite (5%) (Merriman and Hards, 2000). The boundary of the Pomeroy Granite can be inferred for a short distance to the northwest on the opposite side of Murnells Road. At this point there are exposures of dolerite and gabbro, part of the Tyrone Basic Plutonic Complex. These basic rocks have undergone thermal metamorphism through contact with the Pomeroy Granite resulting in the formation of pyroxene-hornfels. | |
| Importance: | |
Craiganawork is the best locality to view the otherwise poorly-exposed Pomeroy Granite and its relationship with thermally metamorphosed country rock of the Tyrone Basic Plutonic Complex. The granite exposures are the freshest so far found and therefore provide the best chance of establishing a date of intrusion via geochronology. If dating is successful, the relationship of Pomeroy with similar granites and surrounding country rocks may be revealed. Further geochemical investigation is required to establish source and mode of emplacement for this and related granites. | |
| Interpretation: | |
The age of the Pomeroy Granite remains uncertain. A thermally metamorphosed contact with early Ordovician Tyrone Basic Plutonic Complex indicates intrusion after obduction of the Tyrone Ophiolite as suggested by Hutton et al. (1985). The fabric in the granite at the margin may relate in part to forceful intrusion of granite magma. The granite must have been sourced from below the obducted ophiolite but current thinking places little certainty on the role of mantle, pre-existing and newly generated crust in the orogenic setting. The relationship between the Pomeroy Granite, Slieve Gallion and similar granites (Beragh and Carrickmore) with gneissose rocks of the Corvanaghan Formation may provide further information relating to their mode and timing of emplacement. | |
| Conclusions: | |
Pomeroy and related plutons most resemble the younger Caledonian granites of late Ordovician or Silurian age. The field relationship with Lower, Middle and Upper Devonian sandstones that overly the granites supports a younger Caledonian age for the suite however, it should be noted that these granites are not seen to intrude Ordovician sediments. It is hoped that radiometric age dating (NIGL work in progress) will shed light on the age and relationships of the Pomeroy Granite Pluton. | |
| Notes: | |
For information and references on sites within the Tyrone Basic Plutonic Complex see the following sites: Key Site 580 - Black Rock Key Site 581 - Scalp Hill For information and references on sites within the Tyrone Volcanic Group see the following sites: Key Site 582 - Mveela More Key Site 583 - Creggan Key Site 584 - Copney Hill Key Site 585 - Beaghbeg Key Site 586 - Bonnety Bush, Altihaskey Key Site 587 - Tullybrick Key Site 588 - Stuhanleanantawey Burn For information and references on other Granitoid sites within the Caledonian Complexes of N. Ireland see the following sites: Key Site 589 - Cashel Rock Key Site 590 - Craigballyharky and Craigbardahessiagh Key Site 592 - Tintagh, Slieve Gallion Key Site 593 - Loughmacrory Key Site 594 - Cushendun 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: | Granite, Sandstone |
| Structures: | Caledonian, pluton |
| Relations: | Intrusion |
| Access | |
|---|---|
| Approach: | Access is via farm tracks and fields from Murnells Road. |
| Management: | |
Given the extensive natural exposure, hammering or sampling restrictions are not necessary at this site. Intrusive granitoids such as the Pomeroy Granite are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration has previously been carried out throughout central Tyrone. The area which includes this site is likely to attract further exploration activity in the future. | |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1886. 1:63,360 Geological Sheet 14 (Cushendall). Dublin, Ordnance Survey for Geological Survey of Ireland. GEOLOGICAL SURVEY OF NORTHERN IRELAND, 1979. Pomeroy, Northern Ireland Sheet 34. Solid. 1:50,000. (Southampton: Ordnance Survey for the Geological Survey of Northern Ireland). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 04 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Craiganawork, Pomeroy, County Tyrone, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=591. Accessed on 2026-11-06. |
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