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The geometry and structural evolution of a crustal-scale Caledonian fold complex: the Ballybofey Nappe, northwest Ireland

Published online by Cambridge University Press:  01 May 2009

G. I. Alsop
G. I. Alsop
Affiliation:
Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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Abstract

The gross geometries exhibited by crustal-scale fold nappes are considered a consequence of both original stratigraphic relationships associated with sub-basin configuration, coupled with the nature of the structural regime and tectonic processes involved in the generation of the nappe pile. The Neo-Proterozoic Dalradian metasediments of northwestern Ireland provide a well-constrained and correlatable stratigraphy which defines a sequence of sub-reclined, tight-isoclinal Caledonian (c. 460 Ma) fold nappes. Within this fold complex, the dominant structure is the crustal-scale Ballybofey Nappe, which may be traced for 40 km along strike and is responsible for a regional (500 km2) stratigraphie inversion. The gentle, NE-plunging attitude of this fold results in a complete spectrum of tectonic levels and deformation gradients being exposed. Relatively low strains in the upper fold limb gradually increase down through the nappe, resulting in the generation of composite foliations and lineations and the development of a 10 km thick shear zone which culminates in a high strain basal detachment with underlying pre-Caledonian basement. The Ballybofey Nappe nucleated and propagated along a major zone of lateral sedimentary facies variation, coincident with the margin of a major Dalradian sub-basin. The large amplitude of the nappe is strongly influenced by the lateral heterogeneity within the metasedimentary sequence, and is associated with a minimum of 25–30 km ESE-directed translation concentrated within the overturned limb. Additional significant displacement is also focused along the basal décollement. Generation of the nappe complex resulted in significant crustal thickening and amphibolite facies metamorphism consistent with 15–18 km of burial, induced by a sequence of nappes propagating in the direction of overshear. The ESE-directed translation of the major fold nappes is away from the Caledonian foreland and a gravity-driven mechanism of nappe emplacement is suggested. Rigorous structural analysis within the cohesive stratigraphie framework enables relationships between the tectonic evolution and stratigraphic patterns to be distinguished, thus allowing models of fold nappe generation and mid-crustal deformation to be evaluated.

Type
Articles
Information
Geological Magazine , Volume 131 , Issue 4 , July 1994 , pp. 519 - 537
Copyright
Copyright © Cambridge University Press 1994

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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.CrossRefGoogle Scholar
Alsop, G. I. 1992 a. Late Caledonian sinistral strike-slip displacement across the Leannan Fault System, north-west Ireland. Geological Journal 27, 119–25.CrossRefGoogle Scholar
Alsop, G. I. 1992 b. Gravity-driven extensional collapse of an oblique ductile thrust; the Ballybofey Slide, north west Ireland. Irish Journal of Earth Sciences 11, 165–75.Google Scholar
Alsop, G. I. 1992 c. Progressive deformation and the rotation of contemporary fold axes in the Ballybofey Nappe, northwest Ireland. Geological Journal 27, 271–85.CrossRefGoogle Scholar
Alsop, G. I. 1992 d. Reversals in the polarity of structural facing across an early ductile thrust; the Central Donegal Slide, northwest Ireland. Geological Journal 27, 3–14.CrossRefGoogle Scholar
Alsop, G. I. 1993. Sequential generation of listric shear bands during protracted ductile thrusting within the Ballybofey Nappe, northwest Ireland. Irish Journal of Earth Sciences 12, 1–12.Google Scholar
Alsop, G. I. 1994. Relationships between distributed and localised shear in the tectonic evolution of a Caledonian fold and thrust zone, northwest Ireland. Geological Magazine 131, 123–36.CrossRefGoogle Scholar
Alsop, G. I. & Holdsworth, R. E. 1993. The distribution, geometry and kinematic significance of Caledonian buckle folds in the western Moine Nappe, northwestern Scotland. Geological Magazine 130, 353–62.CrossRefGoogle 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 a. Caledonian extension in the north Irish Dalradian: implications for the timing and activation of gravity collapse. Journal of the Geological Society, London 150, 33–6.CrossRefGoogle Scholar
Alsop, G. I. & Hutton, D. H. W. 1993 b. Major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: implications for Caledonian tectonics and mid-crustal shear zones. Geological Magazine 130, 233–44.CrossRefGoogle Scholar
Alsop, G. I. & Hutton, D. H. W. 1994. Reply to discussion on major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: implications for Caledonian tectonics and mid-crustal shear zones. Geological Magazine 131, 419–21.Google Scholar
Alsop, G. I. & Jones, C. S. 1991. A review and correlation of Dalradian stratigraphy in the SW/cental Ox Mountains and southern Donegal, 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
Baudin, T., Marquer, D. & Persoz, F. 1993. Basement-cover relationships in the Tambo nappe (Central Alps, Switzerland): geometry, structure and kinematics. Journal of Structural Geology 15, 543–53.CrossRefGoogle Scholar
Borradaile, G. J. 1974. The structure of the Moine-like rocks near Lough Derg, County Donegal, Eire. Geological Journal 9, 61–4.CrossRefGoogle Scholar
Brewer, J. A. & Smythe, D. K. 1984. MOIST and the continuity of crustal reflector geometry along the Caledonian-Appalachian orogen. Journal of the Geological Society, London 141, 105–20.CrossRefGoogle Scholar
Butler, R. W. H. 1992. Structural evolution of the western Chartreuse fold and thrust system, NW French Subalpine chains. In Thrust Tectonics (ed. McClay, K. R.), pp. 287–98. London: Chapman & Hall.CrossRefGoogle Scholar
Dietrich, D. & Casey, M. 1989. A new tectonic model for the Helvetic nappes. In Alpine Tectonics. (eds Coward, M. P., Dietrich, D. and Park, R. G.), pp. 47–63. Geological Society of London Special Publication no. 45.Google Scholar
Escher, A. & Watterson, J. 1974. Stretching fabrics, folds and crustal shortening. Tectonophysics 22, 223–31.CrossRefGoogle Scholar
Escher, A., Masson, H. & Steck, A. 1993. Nappe geometry in the western Swiss Alps. Journal of Structural Geology 15, 501–9.CrossRefGoogle Scholar
Froitzheim, N. 1992. Formation of recumbent folds during synorogenic crustal extension (Austroalpine nappes Switzerland). Geology 20, 923–6.2.3.CO;2>CrossRefGoogle Scholar
Harris, A. L. & Pitcher, W. S. 1975. The Dalradian Supergroup. In A correlation of Precambrian rocks in the British Isles (eds Harris, A. L. et al. ), pp. 52–75. Special Report of the Geological Society, London no. 6.Google Scholar
Harris, D. H. M. 1993. The Caledonian evolution of the Laurentian margin in western Ireland. Journal of the Geological Society, London 150, 669–72.CrossRefGoogle Scholar
Hatcher, R. D. & Hooper, R. J. 1992. Evolution of crystalline thrust sheets in the internal parts of mountain chains. In Thrust Tectonics (ed. McClay, K. R.), pp. 217–33. London: Chapman & Hall.CrossRefGoogle Scholar
Holdsworth, R. E. 1989. The geology and structural evolution of a Caledonian fold and ductile thrust zone, Kyle of Tongue region, Sutherland, northern Scotland. Journal of the Geological Society, London 146, 809–23.CrossRefGoogle Scholar
Holdsworth, R. E. & Grant, C. J. 1990. Convergencerelated ‘dynamic spreading’ in a mid-crustal ductile thrust zone: a possible orogenic wedge model. In Deformation Mechanisms, Rheology and Tectonics (eds Knipe, R. J. and Rutter, E. H.), pp. 491–500. Special Publication of the Geological Society, London no. 54.Google Scholar
Hutton, D. H. W. 1983. Deformational history of an area with well developed tectonic slides: Dalradian rocks of Horn Head, NW Irish Caledonides. Transactions of the Royal Society of Edinburgh, Earth Sciences 73, 151–71.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.CrossRefGoogle Scholar
Klemperer, S. L., Ryan, P. D. & Snyder, D. B. 1991. A deep seismic reflection transect across the Irish Caledonides. Journal of the Geological Society, London 148, 149–64.CrossRefGoogle Scholar
Malavieille, J. 1987. Extensional shearing deformation and kilometer-scale ‘a’-type folds in a Cordilleran metamorphic core complex (Raft River Mountains, northwestern Utah). Tectonics 6, 423–48.CrossRefGoogle Scholar
Mancel, P. & Merle, O. 1987. Kinematics of the northern part of the Simplon Line (Central Alps). Tectonophysics 135, 265–75.CrossRefGoogle Scholar
Max, M. D. & Long, C. B. 1985. Pre-Caledonian basement in Ireland and its cover relationships. Geological Journal 20, 341–6.CrossRefGoogle Scholar
Pfiffner, O. A. 1993. The structure of the Helvetic nappes and its relation to mechanical stratigraphy. Journal of Structural Geology 15, 511–21.CrossRefGoogle 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. & Cambray, F. W. 1964. The Leannan Fault. Quarterly Journal of the Geological Society of London 120, 241–73.CrossRefGoogle Scholar
Pitcher, W. S. & Shackleton, R. M. 1966. On the correlation of certain lower Dalradian successions in northwest Donegal. Geological Journal 5, 149–56.CrossRefGoogle 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.CrossRefGoogle Scholar
Platt, J. P. 1982. Emplacement of a fold-nappe, Betic Orogen, southern Spain. Geology 10, 97–102.2.0.CO;2>CrossRefGoogle Scholar
Platt, J. P., Van Den Eeckhout, B., Janzen, E., Konert, G., Simon, O. J. & Weuermars, R. 1983. The structure and tectonic evolution of the Aguilon fold-nappe, Sierra Alhamilla, Betic Cordilleras, SE Spain. Journal of Structural Geology 5, 519–38.CrossRefGoogle Scholar
Powell, D. & Phillips, W. E.A. 1985. Time of deformation in the Caledonian Orogen of Britain and Ireland. In The Nature and Timing of Orogenic Activity in the Caledonian Rocks of the British Isles (ed. Harris, A. L.), pp. 17–40. Memoir of The Geological Society of London no. 9.Google Scholar
Ramsay, J. G. 1967. Folding and Fracturing of Rocks. New York: McGraw Hill.Google Scholar
Ramsay, J. G. 1981. Tectonics of the Helvetic nappes. ln Thrust and Nappe Tectonics (eds. McClay, K. R. and Price, N. J.), pp. 293–309. Geological Society of London Special Publication no. 9.Google Scholar
Ramsay, J. G. 1989. Fold and fault geometry in the western Helvetic nappes of Switzerland and France and its implications for the evolution of the arc of the western Alps. In Alpine Tectonics (eds Coward, M. P., D. Dietrich and Park, R. G.), pp. 33–45. Geological Society of London Special Publication no. 45.Google Scholar
Ramsay, J. G., Casey, M. & Kligfield, R. 1983. Role of shear in development of the Helvetic fold-thrust belt of Switzerland. Geology 11, 439–42.2.0.CO;2>CrossRefGoogle Scholar
Ridley, J. 1986. Parallel stretching lineations and fold axes oblique to displacement direction-a model and observations. Journal of Structural Geology 8, 647–54.CrossRefGoogle Scholar
Rowan, M. G. & Kligfield, R. 1992. Kinematics of largescale asymmetric buckle folds in overthrust shear: an example from the Helvetic nappes. In Thrust Tectonics (ed. McClay, K. R.), pp. 165–73. London: Chapman & Hall.CrossRefGoogle Scholar
Ryan, P. D. & Dewey, J. F. 1991. A geological and tectonic cross-section of the Caledonides of western Ireland. Journal of the Geological Society, London 148, 173–80.CrossRefGoogle Scholar
Sanders, I. S., Daly, J. S. & Davies, G. R. 1987. Late Proterozoic high-pressure granulite facies metamorphism in the north-east Ox inlier, north-west Ireland. Journal of Metamorphic Geology 5, 69–85.CrossRefGoogle Scholar
Sanderson, D. J. 1973. The development of fold axes oblique to the regional trend. Tectonophysics 16, 55–70.CrossRefGoogle Scholar
Sanderson, D. J., Andrews, J. R., Phillips, W. E. A. & Hurron, D. H. W. 1980. Deformation studies in the Irish Caledonides. Journal of the Geological Society, London 137, 289–302.CrossRefGoogle Scholar
Skjernaa, L. 1980. Rotation and deformation of randomly oriented planar and linear structures in progressive simple shear. Journal of Structural Geology 2, 101–9.CrossRefGoogle Scholar