Hostname: page-component-7479d7b7d-767nl Total loading time: 0 Render date: 2024-07-11T05:22:10.499Z Has data issue: false hasContentIssue false
  • English
  • Français

Basement fractures in North Wales: their recognition and control on Caledonian deformation

Published online by Cambridge University Press:  01 May 2009

I. Wilkinson  and
M. Smith
I. Wilkinson
Affiliation:
Department of Geology, University College of Wales, Aberystwyth, Dyfed, SY23 3DB, Wales
M. Smith
Affiliation:
British Geological Survey (NERC), Bryn Eithyn Hall, Llanfarian, Aberystwyth, SY23 4BY
Get access Rights & Permissions [Opens in a new window]

Abstract

A detailed survey of the patterns of regional deformation in North Wales has revealed the presence of several discrete, linear zones of anomalous deformation. These zones are distinguished by atypical finite strain values, intense tight to isoclinal folding, non-axial planar cleavages and high metamorphic gradients. A history of prolonged tectonic activity along these zones is indicated by their influence on sedimentation and volcanism. It is proposed that these zones reflect the deformation of the Lower Palaeozoic cover above pre-existing basement fractures. These basement fractures form a framework which divides North Wales into a series of blocks and sub-blocks. The end-Caledonian deformation is explained by a transpression model dominated by SE-directed shear with minor components of strike-slip localized in these zones. The application of this model to other parts of the Welsh Basin is briefly considered.

Type
Articles
Information
Geological Magazine , Volume 125 , Issue 3 , May 1988 , pp. 301 - 306
Copyright
Copyright © Cambridge University Press 1988

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Baker, J. W. 1971. Intra–Lower Palaeozoic faults in the southern Irish Sea area. Geological Magazine 108, 501–9.CrossRefGoogle Scholar
Bates, D. E. B. 1974. The structure of the Lower Palaeozoic rocks of Anglesey, with special reference to faulting. Geological Journal 9, 39–60.CrossRefGoogle Scholar
British, Geological Survey. 1987. 1:25000 Sheet, SH64/65, Snowdon.Google Scholar
Campbell, S. D. G., Reedman, A. J. & Howells, M. F. 1985. Regional variations in cleavage and fold development in North Wales. Geological Journal 20, 43–52.CrossRefGoogle Scholar
Campbell, S. D. G., Howells, M. F., Smith, M. & Reedman, A. J. 1988. A Caradoc failed rift within the Ordovician marginal basin of Wales. Geological Magazine 125, 257–66CrossRefGoogle Scholar
Coward, M. P. & Siddans, A. W. B. 1979. The tectonic evolution of the Welsh Caledonides, In The Caledonides of the British Isles–Reviewed (ed. Harris, A. L., Holland, C. H., Leake, B. E.), pp. 187–98. Special Publication of the Geological Society of London no. 8. Edinburgh: Scottish Academic Press.Google Scholar
Craig, J. 1987. The structure of the Llangranog Lineament, West Wales: a Caledonian transpression zone. Geological Journal 22, 167–81.CrossRefGoogle Scholar
Dewey, J. F. 1969. Structure and sequence in the paratectonic British Caledonides. Memoirs of the American Association of Petroleum Geologists 12, 309–35.Google Scholar
Dimberline, A. J. & Woodcock, N. H. 1987. The southeast margin of the Wenlock turbidite system, mid-Wales. Geological Journal 22, 73–86.CrossRefGoogle Scholar
Fitches, W. R. & Campbell, S. D. G. 1987. Tectonic evolution of the Bala Lineament in the Welsh Basin. Geological Journal 22, 131–53.CrossRefGoogle Scholar
Gibbons, W. 1983. The Monian ‘Penmynyyd Zone of Metamorphism’ in Llyn, North Wales. Geological Journal 18, 21–41.CrossRefGoogle Scholar
Gibbons, W. 1987. Menai Strait fault system: an early Caledonian terrane boundary in North Wales. Geology, 15, 744–7.2.0.CO;2>CrossRefGoogle Scholar
Greenly, E. 1919. Geology of Anglesey. Memoir of Geological Survey, Great Britain, 2 vols, pp. 980.Google Scholar
Howells, M. F., Reedman, A. J. & Leveridge, B. E. 1985. Geology of the country around Bangor. Explanation for 1:50000 geological sheet, British Geological Survey Sheet 106, England and Wales.Google Scholar
Howells, M. F., Reedman, A. J. & Campbell, S. D. G. 1986. The submarine eruption and emplacement of the Lower Rhyolitic Tuff Formation (Ordovician), North Wales. Journal of the Geological Society of London 143, 411–23.CrossRefGoogle Scholar
Howells, M. F., Campbell, S. D. G., Reedman, A. J. & Tunnicliff, S. P. 1987. A fissure-controlled acidic volcanic centre (Ordovician) at Yr Arddu, North Wales. Geological Journal 22, 133–49.CrossRefGoogle Scholar
Kokelaar, B. P. 1979. Tremadoc to Llanvirn volcanism on the southeastern side of the Harlech Dome (Robell Fawr) North Wales. In The Caledonides of the British Isles – Reviewed (ed. Harris, A. L., Holland, C. H., Leake, B. E.), pp. 591–96. Special Publication of the Geological Society of London no 8.Google Scholar
Kokelaar, B. P., Howells, M. F., Bevins, R. E., Roach, R. A. & Dunkley, P. N. 1984. The Ordovician marginal basin of Wales. In Marginal Basin Geology: Volcanic and Associated Sedimentary and Tectonic processes in Modern and Ancient Marginal Basins (ed. Kokelaar, B. P., Howells, M. F.), pp. 245–69. Special publication of the Geological Society of London no. 16. Oxford: Blackwell.Google Scholar
Murphy, F. C. 1985. Non-axial planar cleavage and Caledonian sinistral transpression in eastern Ireland. Geological Journal 20, 257–79.CrossRefGoogle Scholar
Reedman, A. J., Leveridge, B. E. & Evans, R. B. 1984. The Arvon Group (‘Arvonian’) of North Wales. Proceedings of the Geologists Association of London 95, 313–21.CrossRefGoogle Scholar
Roberts, B. 1967. The succession and structure in the Llwyd Mawr syncline, Caernarvonshire, North Wales. Geological Journal 5, 369–90.CrossRefGoogle Scholar
Roberts, B. 1979. The Geology of Snowdonia and Llyn: An Outline and Field Guide. Bristol: Adam Hilger, 183 pp.Google Scholar
Roberts, B. & Merriman, R. J. 1985. The distinction between Caledonian burial and regional metamorphism in metapelites from North Wales: an analysis of isocyst patterns. Journal of the Geological Society of London 142, 615–24.CrossRefGoogle Scholar
Sanderson, D. J. & Marchini, W. R. D. 1984. Transpression. Journal of Structural Geology 6, 449–58.CrossRefGoogle Scholar
Shackleton, R. M. 1954. The structural evolution of North Wales. Liverpool and Manchester Geological Journal 1, 261–96.CrossRefGoogle Scholar
Smallwood, S. D. 1986. Sedimentation across the Tywi lineament, mid-Wales. Philosophical Transactions of the Royal Society of London A 317, 279–88.Google Scholar
Smith, M. 1987. The Tremadoc ‘Thrust’ Zone in Southern Central Snowdonia. Geological Journal 22, 119–29.CrossRefGoogle Scholar
Smith, R. D. A. 1987. Structure and deformation history of the central Wales synclinorium, north-east Dyfed: evidence for a long-lived basement structure. Geological Journal 22, 183–98.CrossRefGoogle Scholar
Soper, N. J., Webb, B. C. & Woodcock, N. H. 1987. Late Caledonian (Acadian) transpression in north west England: timing, geometry and geotectonic significance. Proceedings of the Yorkshire Geological Society.CrossRefGoogle Scholar
Wilkinson, I. 1987. A finite study of the Ordovician rocks of Snowdonia, North Wales, and its implications for a regional strain model. Geological Journal 22, 95–105.CrossRefGoogle Scholar
Woodcock, N. H. 1984. Early palaeozoic sedimentation and tectonics in Wales. Proceedings of the Geologists Association London 95, 323–35.CrossRefGoogle Scholar