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Ordovician volcanism in the Welsh Borderland

Published online by Cambridge University Press:  01 May 2009

P. T. Leat  and
R. S. Thorpe
P. T. Leat
Affiliation:
Department of Geology, Imperial College of Science and Technology, London SW7 2BP, U.K.
R. S. Thorpe
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, U.K.
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Abstract

Basaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 6 , November 1986 , pp. 629 - 640
Copyright
Copyright © Cambridge University Press 1986

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References

Allen, P. M. 1982. Lower Palaeozoic volcanism in Wales, the Welsh Borderland, Avon, and Somerset. In Igneous Rocks of the British Isles (ed. Sutherland, D. S.), pp. 65–91. Chichester: J. Wiley and Sons.Google Scholar
Bevins, R. E. 1982. Petrology and geochemistry of the Fishguard Volcanic Complex, Wales. Geological Journal 17, 1–21.CrossRefGoogle Scholar
Bevins, R. E., Kokelaar, B. P. & Dunkley, P. N. 1984. Petrology and geochemistry of Lower to Middle Ordovician igneous rocks in Wales: a volcanic arc to marginal basin transition. Proceedings of the Geologists' Association 95, (4), 337–47.CrossRefGoogle Scholar
Bevins, R. E. & Rowbotham, G. 1983. Low-grade metamorphism within the Welsh sector of the paratectonic Caledonides. Geological Journal 18, 141–67.CrossRefGoogle Scholar
Blyth, F. G. H. 1938. Pyroclastic rocks from the Stapeley Volcanic Group at Knotmoor, near Minsterley, Shropshire. Proceedings of the Geologists' Association 49, 392–404.CrossRefGoogle Scholar
Christiansen, R. L. & Lipman, P. W. 1972. Cenozoic volcanism and plate-tectonic evolution of the Western United States. II. Late Cenozoic. Philosophical Transactions of the Royal Society of London A271, 249–84.Google Scholar
Coish, R. A. & Taylor, L. A. 1979. The effects of cooling rate on texture and pyroxene chemistry in DSDP Leg 34 basalt: a microprobe study. Earth and Planetary Science Letters 42, 389–398.CrossRefGoogle Scholar
Cole, J. W. 1981. Genesis of lavas of the Taupo volcanic zone, North Island, New Zealand. Journal of Volcanology and Geothermal Research 10, 317–37.CrossRefGoogle Scholar
Croudace, I. W. 1982. The geochemistry and petrogenesis of the Lower Palaeozoic granitoids of the Llyn Peninsula, North Wales. Geochimica et Cosmochimica Acta 46, 609–22.CrossRefGoogle Scholar
Davies, G., Gledhill, A. & Hawkesworth, C. 1985. Upper crustal recycling in southern Britain: evidence from Nd and Sr isotopes. Earth and Planetary Science Letters 75, 1–12.CrossRefGoogle Scholar
Earp, J. R. & Hains, B. A. 1971. The Welsh Borderland. British Regional Geology. H.M.S.O., 3rd edn.Google Scholar
Ewart, A. 1979. A review of the mineralogy and chemistry of Tertiary-Recent dacitic, latitic, rhyolitic and related salic volcanic rocks. In Trondhjemites, Dacites and Related Rocks (ed. Barker, F.), pp. 13–121. Amsterdam: Elsevier.CrossRefGoogle Scholar
Fitton, J. G., Thirlwall, M. F. & Hughes, D. J. 1982. Volcanism in the Caledonian belt of Britain. In Andesites: Orogenic Andesites and Related Rocks (ed. Thorpe, R. S.), pp. 611–36. Chichester: J. Wiley.Google Scholar
Floyd, P. A. & Winchester, J. A. 1978. Identification and discrimination of altered and metamorphosed volcanic rocks using immobile elements. Chemical Geology 21, 291–306.CrossRefGoogle Scholar
Grieg, D. C., Wright, J. E., Hains, B. A. & Mitchell, G. H. 1968. Geology of the Country around Church Stretton, Craven Arms, Wenlock Edge and Brown Clee. Memoir of the Geological Survey of Great Britain 166. London: H.M.S.O.Google Scholar
Henderson, P. & Williams, C. T. 1981. Application of intrinsic Ge detectors to the instrumental neutron activation analysis for rare earth elements in rocks and minerals. Journal of Radioanalytical Chemistry 67, 445–52.CrossRefGoogle Scholar
Jones, O. T. & Pugh, W. J. 1949. An early Ordovician shoreline in Radnorshire, near Builth Wells. Quarterly Journal of the Geological Society of London 105, 65–99.CrossRefGoogle 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.Google Scholar
Lambert, R. St. J. Holland, J. G. & Owen, P. F. 1974. Chemical petrology of a suite of calc-alkaline lavas from Mount Ararat, Turkey. Journal of Geology 82, 419–38.CrossRefGoogle Scholar
Lapworth, C. & Watts, W. W. 1894. The geology of south Shropshire. Proceedings of the Geologists' Association 13, 297–355.CrossRefGoogle Scholar
Leat, P. T., Jackson, S. E., Thorpe, R. S. And Stillman, C. J. 1986. Geochemistry of bimodal basalt-subalkaline/peralkaline rhyolite provinces within the Southern British Caledonides. Journal of the Geological Society of London 143, 259–273.CrossRefGoogle Scholar
Leat, P. T. & Thorpe, R. S. 1986. Geochemistry of an Ordovician basalt-trachybasalt-subalkaline/peralkaline rhyolite association from the Lleyn Peninsula, N. Wales, U.K. Geological Journal 21, 29–43.CrossRefGoogle Scholar
Le Bas, M. J. 1962. The role of aluminium in igneous clinopyroxenes with relation to their parentage. American Journal of Science 260, 267–288.CrossRefGoogle Scholar
Leitch, E. C. 1984. Marginal basins of the S. W. Pacific and the preservation and recognition of their ancient analogues: a review. 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. 97–108. Special Publication of the Geological Society of London, no. 16.Google Scholar
Lynas, B. D. T. 1983. Two new Ordovician volcanic centres in the Shelve inlier, Powys, Wales. Geological Magazine 120, 535–42.CrossRefGoogle Scholar
Lynas, B. D. T., Rundle, C. C., & Sanderson, R. W. 1985. A note on the age and pyroxene chemistry of the igneous rocks of the Shelve inlier, Welsh Borderland. Geological Magazine 122, 641–647.CrossRefGoogle Scholar
Mitchell, A. H. G. 1984. The British Caledonides: Interpretations from Cenozoic analogues. Geological Magazine 121, (1), 35–46.CrossRefGoogle Scholar
Pearce, J. A. 1980. Geochemical evidence for the genesis and eruptive setting of lavas from Tethyan ophiolites. In Proceedings of the International Ophiolite Symposium, Nicosia, pp. 261–72. Cyprus.Google Scholar
Pearce, J. A. 1982. Trace element characteristics of lavas from destructive plate boundaries. In Andesites: Orogenic Andesites and Related Rocks (ed. Thorpe, R. S.), pp. 525–48. Chichester: J. Wiley.Google Scholar
Pearce, J. A. 1983. Role of sub-continental lithosphere in magma genesis at active continental margins. In Continental Basalts and Mantle Xenoliths (ed. Hawkesworth, C. J. Norry, M. J.), pp. 230–49, Nantwich, Cheshire: Shiva.Google Scholar
Pearce, J. A., Harris, N. B. W. & Tindle, A. G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25 (4), 956–83.CrossRefGoogle Scholar
Pearce, J. A. & Norry, M. J. 1979. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contributions to Mineralogy and Petrology 69, 33–47.CrossRefGoogle Scholar
Phillips, W. E. A., Stillman, C. J. & Murphy, T. 1976. A Caledonian plate tectonic model. Journal of the Geological Society of London 132, 579–609.CrossRefGoogle Scholar
Potts, P. J., Webb, P. C. & Watson, J. S. 1984. Energy-dispersive X-ray fluorescence analysis of silicate rocks for major and trace elements. X-ray Spectronomy 13, 2–15.Google Scholar
Sanderson, R. W. & Cave, R. 1980. Silurian volcanism in the central Welsh Borderland. Geological Magazine 117, 455–62.CrossRefGoogle Scholar
Saunders, A. D. & Tarney, J. 1979. The geochemistry of basalts from a back-arc spreading centre in the East Scotia Sea. Geochimica et Cosmochimica Acta 43, 555–72.CrossRefGoogle Scholar
Saunders, A. D. & Tarney, J. 1984. Geochemical characteristics of basaltic volcanism within back-arc basins. 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. 59–76. Special Publication of the Geological Society of London, no. 16.Google Scholar
Smith, I. E. M., Chappell, B. W. Ward, G. K. & Freeman, R. S. 1977. Peralkaline rhyolites associated with andesitic arcs of the southwest Pacific. Earth and Planetary Science Letters 37, 230–6.CrossRefGoogle Scholar
Stillman, C. J. & Francis, E. H. 1979. Caledonide volcanism in Britain and Ireland. In The Caledonides of the British Isles – Reviewed (ed. Harris, A. L., Holland, C. H. and Leake, B. E.), pp. 557–77. Special Publication of the Geological Society of London, no. 8.Google Scholar
Thompson, R. N., Dickin, A. P., Gibson, I. L. & Morrison, M. A. 1982. Elemental fingerprints of isotopic contamination of Hebridean Palaeocene mantle-derived magmas by Archaean sial. Contributions to Mineralogy and Petrology 79, 159–168.CrossRefGoogle Scholar
Thorpe, R. S. 1979. Late Precambrian igneous activity in southern Britain. In The Caledonides of the British Isles – Reviewed (ed. Harris, A. L. Holland, C. H. Leake, B. E.), pp. 579–84. Special Publication of the Geological Society of London, no. 8.Google Scholar
Thorpe, R. S., Beckinsale, R. D., Patchett, P. J., Piper, J. D. A., Davis, G. R. & Evans, J. A. 1984. Crustal growth and Late Precambrian–early Palaeozoic plate tectonic evolution of England and Wales. Journal of the Geological Society of London 141, 521–36.CrossRefGoogle Scholar
Watts, W. W. 1885. On the igneous and associated rocks of the Breidden Hills in east Montgomeryshire and west Shropshire. Quarterly Journal of the Geological Society of London 41, 532–46.CrossRefGoogle Scholar
Watts, W. W. 1925. The geology of south Shropshire. Proceedings of the Geologists' Association 36 (4), 322–93.Google Scholar
Whittard, W. F. 1952. A geology of south Shropshire. Proceedings of the Geologists' Association 63, 143–97.CrossRefGoogle Scholar
Whittard, W. F. 1979. An account of the Ordovician rocks of the Shelve inlier in west Salop and part of north Powys. Bulletin of the British Museum Natural History Geology Series 33, 1–69.Google Scholar
Wood, D. A. 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establish the nature of crustal contamination of basaltic lavas of the British Tertiary Volcanic Province. Earth and Planetary Science Letters 50, 11–30.CrossRefGoogle Scholar
Wood, D. A., Gibson, I. L. & Thompson, R. N. 1976. Elemental mobility during zeolite facies metamorphism of the Tertiary basalts of eastern Iceland. Contributions to Mineralogy and Petrology 55, 241–54.CrossRefGoogle Scholar
Woodcock, N. H. 1984 a. The Pontesford Lineament, Welsh Borderland. Journal of the Geological Society of London 141, 1001–14.CrossRefGoogle Scholar
Woodcock, N. H. 1984 b. Early Palaeozoic sedimentation and tectonics in Wales. Proceedings of the Geologists' Association 95 (4), 323–35.CrossRefGoogle Scholar
Ziegler, A. M., Mckerrow, W. S., Burne, R. V. & Baker, P. E. 1969. Correlation and environmental setting of the Skomer Volcanic Group, Pembrokeshire. Proceedings of the Geologists' Association 80, 409–39.CrossRefGoogle Scholar