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Major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: implications for Caledonian tectonics and mid-crustal shear zones

Published online by Cambridge University Press:  01 May 2009

G. I. Alsop  and
D. H. W. Hutton
G. I. Alsop
Affiliation:
Department of Geological Sciences, University of Durham, DH1 3LE, U.K.
D. H. W. Hutton
Affiliation:
Department of Geological Sciences, University of Durham, DH1 3LE, U.K.
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Abstract

The dominant structure controlling the disposition of Dalradian stratigraphy in mid-Ulster has hitherto been regarded as a southeast-facing gently inclined F1 anticline, a gross geometry modelled on, and thought to be a possible correlative of, the Tay Nappe in Scotland. Remapping of the supposedly inverted southern limb of this major fold reveals that much of it is in fact the correct way up. However, a stratigraphie repetition coupled with a reversal in younging does occur in the Sperrin Mountains, much further south than previously realized. This hitherto unrecognized upward southeast-facing isoclinal Sperrin Nappe is, however, a D2 structure, traceable for at least 40 km along strike and responsible for a regional stratigraphie inversion over an area of 300 km2. Following D2, a major 10 km thick D3 ductile shear zone resulted in translation towards the east-southeast. In the south, this deformation carried the Dalradian over Ordovician volcanics of the Tyrone Igneous Complex along the Omagh Thrust. Penecontemporaneity of magmatism with deformation clearly demonstrates that D3 is Caledonian (Arenig-Llanvirn). This deformation correlates with similar southeast-directed Caledonian thrusting in southern Donegal and Connemara. The apparent absence of Dalradian deformation of this age in southwestern Scotland may imply that Caledonian collision of outboard terranes with the miogeoclinal margin was initiated in Ireland and/or subsequent strike-slip has removed the evidence for deformation of this age from southwestern Scotland. The D3 shear zone in the Sperrin Mountains affects a very large volume of psammitic rocks. Within this shear zone the strain is not markedly higher than surrounding areas; however, its existence is demonstrated by the reorientation of mineral lineations over a large area. Such broad zones of only moderate strain may, we believe, be typical of translatory tectonics in areas of the mid-crust where there is little lithological diversity.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 2 , March 1993 , pp. 233 - 244
Copyright
Copyright © Cambridge University Press 1993

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References

Alsop, G. I. 1991. Gravitational collapse and extension along a mid-crustal detachment: the Lough Derg Slide, northwest Ireland. Geological Magazine 128, 345–54.Google Scholar
Alsop, G. I. 1992 a. Reversals in the polarity of structural facing across an early ductile thrust; the Central Donegal Slide, northwest Ireland. Geological Journal 27, 3–14.Google Scholar
Alsop, G. I. 1992 b. Progressive deformation and the rotation of contemporary fold axes in the Ballybofey Nappe, northwest Ireland. Geological Journal 27, 271–83.Google Scholar
Alsop, G. I. 1992 c. Gravity-driven extensional collapse of an oblique ductile thrust; the Ballybofey Slide, northwest Ireland. Irish Journal of Earth Sciences 11, 165–75.Google Scholar
Alsop, G. I. 1992 d. Late Caledonian sinistral strike-slip displacement across the Leannan Fault System, northwest Ireland. Geological Journal 27, 119–25.Google Scholar
Alsop, G. I. & Hutton, D. H. W. 1990. A review and revision of Dalradian stratigraphy in central and southern Donegal, Ireland. Irish Journal of Earth Sciences 10, 181–98.Google Scholar
Alsop, G. I. & Hutton, D. H. W. 1993. Caledonian extension in the north Irish Dalradian: implications for the timing and activation of gravity collapse. Journal of the Geological Society, London 150, (in press).Google Scholar
Alsop, G. I. & Jones, C. S. 1991. A review and correlation of Dalradian stratigraphy in the SW/central Ox Mountains and southernDonegal, Ireland. Irish Journal of Earth Sciences 11, 99–112.Google Scholar
Arthurs, J. W. 1976. The geology and metalliferous mineral potential of the Sperrin Mountains area. Geological Survey of Northern Ireland report.Google Scholar
Bailey, E. B. & McCallien, W. J. 1934. The metamorphic rocks of north-east Antrim. Transactions of the Royal Society of Edinburgh 58, 163–78.CrossRefGoogle Scholar
Harris, A. L. & Pitcher, W. S. 1975. The Dalradian Supergroup. In A correlation of the Pre-Cambrian rocks of the British Isles (eds Harrison, A. L. and others), pp. 52–75. Geological Society of London Special Report no. 6.Google Scholar
Hartley, J. J. 1933. The geology of northeastern Tyrone and adjacent parts of County Londonderry. Proceedings of the Royal Irish Academy 41B, 218–85.Google Scholar
Hartley, J. J. 1935. The igneous and metamorphic complex of County Tyrone. Proceedings of the Geologists' Association 66, 446–8.Google Scholar
Hartley, J. J. 1936. The age of the igneous series of Slieve Gallion, Northern Ireland. Geological Magazine 73, 226–8.Google Scholar
Hartley, J. J. 1938. The Dalradian rocks of the Sperrin Mountains and adjacent areas in Northern Ireland. Proceedings of the Royal Irish Academy 44B, 141–71.Google Scholar
Hutton, D. H. W. 1979. Tectonic slides: a review and reappraisal. Earth Science Review 15, 151–72.CrossRefGoogle Scholar
Hutton, D. H. W. 1987. Strike-slip terranes and a model for the evolution of the British and Irish Caledonides. Geological Magazine 124, 405–25.Google Scholar
Hutton, D. H. W., Aftalion, M. & Halliday, A. N. 1985. An Ordovician ophiolite in County Tyrone, Ireland. Nature 315, 210–12.Google Scholar
Hutton, D. H. W. & Holland, C. H. 1992. An Arenig-Llanvirn age for the black shales of Slieve Gallion, County Tyrone. Irish Journal of Earth Sciences 11, 187–9.Google Scholar
Leake, B. E., Tanner, P. W. G., Singh, D. & Halliday, A. N. 1983. Major southward overthrusting of the Dalradian rocks of Connemara, Western Ireland. Nature 305, 210–13.Google Scholar
McCallien, W. J. 1931. A contribution to the correlation of the Dalradian rocks of Scotland and Ireland. Geological Magazine 68, 126–33.Google Scholar
McCallien, W. J. 1935. The metamorphic rocks of Inishowen, County Donegal. Proceedings of the Royal Irish Academy 42B, 407–42.Google Scholar
McCallien, W. J. 1936. A note on Dalradian pillow lavas, Strabane, County Tyrone. Proceedings of the Royal Irish Academy 43B, 13–22.Google Scholar
McCallien, W. J. 1937. The geology of the Rathmullan district, Co. Donegal. Proceedings of the Royal Irish Academy 44B, 45–60.Google Scholar
Phillips, W. E. A. 1981. The Orthotectonic Caledonides. In A Geology of Ireland (ed. Holland, C. H.), pp. 17–40. Edinburgh; Scottish Academic Press.Google Scholar
Pitcher, W. S. & Berger, A. R. 1972. The Geology of Donegal: A Study of Granite Emplacement and Unroofing. New York, London: Wiley Interscience, 435 pp.Google Scholar
Pitcher, W. S., Elwell, R. W. D., Tozer, C. F. & Cam-Bray, F. W. 1964. The Leannan Fault. Quarterly Journal of the Geological Society of London 120, 241–73.Google Scholar
Pitcher, W. S., Shackleton, R. M. & Wood, R. S. R. 1971. The Ballybofey Anticline: a solution of the general structure of parts of Donegal and Tyrone. Geological Journal 7, 321–8.Google Scholar
Rogers, G., Dempster, T. J., Bluck, B. J. & Tanner, P. W. G. 1989. A high precision U-Pb age for the Ben Vurich granite: implicationsfor the evolution of the Scottish Dalradian supergroup. Journal of the Geological Society, London 146, 789–98.Google Scholar
Sanders, I. S., Daly, J. S. & Davies, G. R. 1987. Late Proterozoic high-pressure granulite faciès metamor-phism in the north-east Ox inlier, north-west Ireland. Journal of Metamorphic Geology 5, 69–85.Google Scholar
Tanner, P. W. G., Dempster, T. J. & Dickin, A. P. 1989. Time of docking of the Connemara terrane with the Delaney Dome Formation, western Ireland. Journal of the Geological Society, London 146, 389–92.Google Scholar
Van Breeman, O., Halliday, A. N., Johnson, M. R. W. & Bowes, D. R. 1978. Crustal additions in late Precambrian times. In Crustal Evolution in Northwestern Britain and Adjacent Regions (eds. Bowes, R. and Leake, B. E.), pp. 81–106. Geological Journal Special Issue no. 10.Google Scholar
Woodland, A. W. 1977. 1:250,000 map of Ireland, Sheet 1. Geological Survey of Northern Ireland.Google Scholar