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Terrane geochemistry contrasts across the Iapetus Suture in Ireland

Published online by Cambridge University Press:  01 May 2009

P. D. Ryan
Affiliation:
Geology Department, University College, Galway, Ireland
C. J. Stillman
Affiliation:
Geology Department, Trinity College, Dublin 2, Ireland
C. J. Stillman
Affiliation:
Geology Department, Trinity College, Dublin 2, Ireland
S. Pow
Affiliation:
Powergen, Powergen Technology Centre, Ratcliffe on Soar, Nottingham NG11 OEE, UK

Abstract

In the Irish Caledonides, volcanism has been significant in terrane identification and in reconstructions of the Appalachian/Caledonian orogen. Crucial to these reconstructions is the recognition of ocean margins using obducted ocean floor relics (ophiolites) and supra-subduction zone volcanic assemblages. The volcanic rocks provide much evidence for the affinity of a terrane, however, by analogy with present day examples, the ocean floor sediments may provide the best way of tracing both ocean-floor magmatic activity, and continental source areas. This investigation shows that the Irish Lower Palaeozoic volcanogenic terranes can be discriminated in terms of their shale geochemistry, which also gives information on their provenance and environment of deposition. South Mayo shales are dominated by volcaniclastic material derived both from both an arc and from an ophiolitic source. The Northern and Central belts of the Central Terrane show very similar lithogeochemistries, apparently derived in part from intermediate to silicic volcanic complexes. The Ordovician-Silurian inliers that straddle the Suture Zone, here termed the Southern Domain, show a chemistry close to that of the Leinster Terrane, which, coupled with a greater degree of sea-floor weathering, suggests a terrane with sediment of both volcanic and continental provenance being deposited in deeper water further from land. Across the suture the Leinster Terrane shows a mature chemistry which clearly suggests a continental provenance, together with a volcanogenic input from supra-subduction volcanism. This maturity is probably due to slower rates of sedimentation with longer residence times for volcanic detritus, plus the existence of a deeply weathered continental basement.

Type
Articles
Copyright
Copyright © Cambridge University Press 1995

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References

Bjørlykke, K., 1974 a. Depositional history and geochemical composition of the Lower Palaeozoic epicontinental sediments from the Oslo region. Norges Geologisk Undersøkelse 305, 181Google Scholar
Bjørlykke, K., 1974 b. Geochemical and rnineralogical influence of Ordovician island arcs on epicontinental clastic sedimentation. A study of Lower Palaeozoic sedimentation in the Oslo region, Norway. Sedimentology 21, 251–72.CrossRefGoogle Scholar
Boström, K., 1970. Submarine vulcanism as a source for iron. Earth and Planetary Science Letters 9, 348–54.CrossRefGoogle Scholar
Clift, P., & Ryan, P. D., 1994 Geochemical evolution of an island arc, South Mayo, Ireland. Journal of the Geological Society, London 151, 329–42.CrossRefGoogle Scholar
Cullers, R. L., & Graf, J. L., 1984. Rare earth elements in igneous rocks of the continental crust: intermediate and silicic rocks — ore petrogenesis. In Developments in Geochemistry 2: Rare Earth Element Geochemistry (ed. Henderson, P.), pp. 237–49. Amsterdam: Elsevier.Google Scholar
Deer, W. A., Howie, R. A., & Zussman, J., 1967. The Rock Forming Minerals. London: Longmans.Google Scholar
Dewey, J. F., & Ryan, P. D., 1990. The Ordovician evolution of the South Mayo Trough, western Ireland. Tectonics 9, 887901.CrossRefGoogle Scholar
Dewey, J. F., & Shackleton, R. M. 1984. A model for the evolution of the Grampian tract in the early Caledonides and Appalachians. Nature 312, 115–21.CrossRefGoogle Scholar
Duller, P. R., & Floyd, J. D., 1995. Turbidite geochemistry and provenance studies in the Southern Uplands. Geological Magazine 132, 000–000.CrossRefGoogle Scholar
Henderson, P., 1984. General geochemical properties and abundance of Rare Earth Elements. In Developments in Geochemistry 2: Rare Earth Element Geochemistry (ed. Henderson, P.), pp. 129. Amsterdam: Elsevier.Google Scholar
Klemperer, S. L., 1989. Seismic reflection evidence for the location of the Iapetus Suture. Journal of the Geological Society, London 146, 409–12.CrossRefGoogle Scholar
McLennan, S. M., Taylor, S. R., McCulloch, M. T., & Maynard, J. B., 1990. Geochemical and Nd—Sm isotopic composition of deep sea turbidites: Geochemica and Cosmochemica Acta 54, 2015–50.CrossRefGoogle Scholar
Menuge, J. F., Williams, D. M., & O’Connor, P. D., 1995. Silurian turbidites used to reconstruct a volcanic terrane and its Mesoproterozoic basement in the Irish Caledonides. Journal of the Geological Society, London 152, 269–78.CrossRefGoogle Scholar
Morris, J. H., 1987. The Northern Belt of the Longford Down, Ireland and Southern Uplands, Scotland: an Ordovician back-arc basin. Journal of the Geological Society, London 144, 773–86.CrossRefGoogle Scholar
Murphy, F. C., Andersen, T. B., Daly, J. S., Gallagher, V., Graham, J. R., Harper, D. A. T., Johnston, J. D., Kennan, P. S., Kennedy, M. J., Long, C. B., Morris, J. H., O’Keeffe, W. G., Parkes, M., Ryan, P. D., Sloan, M., Stillman, C. J., Tietzsch-Tyler, D., Todd, S. P., & Wrafter, J. P., 1991. An appraisal of Caledonian suspect terranes in Ireland. Irish Journal of Earth Sciences 11, 1141.Google Scholar
Phillips, W. E. A., Stillman, C. J., & Murphy, T., 1976. A Caledonian plate tectonic model. Journal of the Geological Society, London 132, 579609.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
Ryan, P. D., Floyd, P. A., & Archer, J. B., 1980. The stratigraphy and petrochemistry of the Loch Nafooey Group (Tremadocian), western Ireland. Journal of the Geological Society, London 137, 443–58.CrossRefGoogle Scholar
Ryan, P. D., & Williams, D. M., 1985. The shale geochemistry of the Hovin Group, Meldal, Sör Trondelag, Norway. In The Caledonide Orogen—Scandinavia and related areas (eds Gee, D. and Start, B. A.), pp. 429–39. John Wiley and Sons.Google Scholar
Shannon, P. S., 1979. The Lower Palaeozoics of SE Ireland: their tectonic evolution south of the Leinster Granite. In Caledonides of the British Isles — Reviewed (eds Harris, A. L., Holland, C. H. and Leake, B. E.), pp. 281–5. Geological Society of London, Special Publication no. 8.Google Scholar
Stillman, C. J., 1988. Ordovician to Silurian volcanism in the Appalachian—Caledonian Orogen. Inn The Caledonian—Appalachian Orogen (eds Harris, A. L. and Fettes, D. J.), pp. 275–90. Geological Society Special Publication no. 38.Google Scholar
Winchester, J., & Max, M. D., 1982. The geochemistry and origins of the Precambrian rocks of the Rosslare complex, SE Ireland. Journal of the Geological Society, London 139, 309–19.CrossRefGoogle Scholar
Winchester, J., & Max, M. D., 1989. The Pre-Caledonian Iniskea Division of northwest Co. Mayo, Ireland: its geochemistry and probable stratigraphic position. Geological Journal 22, 309–21.CrossRefGoogle Scholar
Wrafter, J. P., & Graham, J. G., 1989. Ophiolitic detritus in the Ordovician sediments of South Mayo, Ireland. Journal of the Geological Society, London 146, 213–15.CrossRefGoogle Scholar