Earth Science Conservation Review
| Tullybrick | Londonderry |
| Site Type: | Stream section |
| Site Status: | ESCR |
| Grid Reference: | H732904 |
| Google maps: | 54.75666,-6.863 |
| Rocks | |
|---|---|
| Rock Age: | Ordovician |
| Rock Name: | Tyrone Volcanic Group |
| Rock Type: | Mylonite, Schist |
| Interest | |
| Minerals: | Chlorite, Sericite |
| Other interest: | Caledonian, fault, Extrusion |
Introduction:
The Tullybrick site is in a stream section in the townland of Tullybrick south of the Moyola Valley and close to the Six Towns. Streambed outcrops extend for a distance of about 600m upstream from the Bridge at [27320 39040]. Access to the site is from the Tullybrick Road via the bridge parapet.
On Portlock's early geological map of the area (1843), the rocks in the vicinity of Tullybrick were represented as "mica schists" and were not distinguished from the metamorphic rocks of the Sperrin Mountains.
On the first edition of the one-inch to the mile scale geological map (Sheet 26, Draperstown, Geological Survey of Ireland, 1882) the rocks at Tullybrick were shown as "chloritic, Talcose & Micaceous Schists of Lower Silurian age". In the memoir, which accompanied the map, Nolan (1884) referred to "shining thin-bedded schists ..." in the nearby Altihaskey Glen.
Hartley (1933) published the first detailed lithological map and description of the central Tyrone Ordovician volcanicplutonic terrane and incorporated the rocks at Tullybrick in a division which he referred to as the "Phyllites and Chloritic Schists of Tullybrick". Hartley considered that the schists at Tullybrick were part of the volcanic tuff and lava (volcanic) series into which they grade.
On the second edition (1:50,000 scale) of Sheet 26(Draperstown) (Geological Survey of Northern Ireland, 1995) the stratigraphy of the volcanic and plutonic rocks of Tyrone and south Londonderry was revised and the rocks at Tullybrick are included within the Tyrone Volcanic Group.
The Tyrone Volcanic Group forms part of the Tyrone-Girvan Sub-Terrane of the Midland Valley Terrane as designated by Bluck et al. (1992). This terrane comprises ophiolitic and arc-volcanic type geological sequences which formed along the Laurentian foreland at the northern margin of the Iapetus Ocean during closure of the Iapetus Ocean during Ordovician times (Hutton et al., 1985).
On Portlock's early geological map of the area (1843), the rocks in the vicinity of Tullybrick were represented as "mica schists" and were not distinguished from the metamorphic rocks of the Sperrin Mountains.
On the first edition of the one-inch to the mile scale geological map (Sheet 26, Draperstown, Geological Survey of Ireland, 1882) the rocks at Tullybrick were shown as "chloritic, Talcose & Micaceous Schists of Lower Silurian age". In the memoir, which accompanied the map, Nolan (1884) referred to "shining thin-bedded schists ..." in the nearby Altihaskey Glen.
Hartley (1933) published the first detailed lithological map and description of the central Tyrone Ordovician volcanicplutonic terrane and incorporated the rocks at Tullybrick in a division which he referred to as the "Phyllites and Chloritic Schists of Tullybrick". Hartley considered that the schists at Tullybrick were part of the volcanic tuff and lava (volcanic) series into which they grade.
On the second edition (1:50,000 scale) of Sheet 26(Draperstown) (Geological Survey of Northern Ireland, 1995) the stratigraphy of the volcanic and plutonic rocks of Tyrone and south Londonderry was revised and the rocks at Tullybrick are included within the Tyrone Volcanic Group.
The Tyrone Volcanic Group forms part of the Tyrone-Girvan Sub-Terrane of the Midland Valley Terrane as designated by Bluck et al. (1992). This terrane comprises ophiolitic and arc-volcanic type geological sequences which formed along the Laurentian foreland at the northern margin of the Iapetus Ocean during closure of the Iapetus Ocean during Ordovician times (Hutton et al., 1985).
| Enlander, I., Dempster, M. & Doughty, P., 2024. Tullybrick, County Londonderry, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=587. Accessed on 2024-12-26 |
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