Hostname: page-component-8448b6f56d-cfpbc Total loading time: 0 Render date: 2024-04-24T23:30:17.264Z Has data issue: false hasContentIssue false
  • English
  • Français

Nd-isotope study of provenance patterns across the British sector of the Iapetus Suture

Published online by Cambridge University Press:  01 May 2009

P. Stone  and
J. A. Evans
P. Stone
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK
J. A. Evans
Affiliation:
NERC Isotope Geosciences Laboratory. Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

The Southern Uplands greywacke succession (Scotland) accumulated at the Laurentian margin of the Iapetus Ocean. It was sequentially incorporated into an imbricate, accretionary thrust complex until closure of the ocean. Thereafter the thrust belt propagated across the suture zone as a foreland thrust belt directed towards the hinterland of Avalonia. A foreland basin migrating ahead of the thrust belt was the depositional site for the southernmost Southern Uplands units and the Windermere Supergroup (English Lake District). A Nd-isotope study has shown that juvenile ophiolitic detritus was introduced into the oldest, mid-Ordovician, Southern Uplands greywackes before two distinct provenance areas evolved: one supplying juvenile andesitic detritus in addition to a quartzo-feldspathic component, the other Proterozoic and exclusively quartzo-feldspathic. Bimodal composition continued into the early Silurian but was overlapped from late in the Ordovician by greywackes with intermediate Nd-isotope composition. This was not a simple mixing effect since the andesitic component is not represented and the necessary juvenile component comes from granodioritic and felsitic lithologies. Intermediate eNd values are then a consistent feature through the Silurian both in the younger strata of the Southern Uplands and in the earliest foreland basin turbidites of the Windermere Supergroup. The transition suggests cessation of volcanicity and erosion of deeper levels of the provenance terrane(s), possibly linked to the evolution of the basin system from active margin, accretion-related, to a foreland setting. To the north of the Southern Uplands terrane, beyond the Southern Upland Fault, a Caradoc to Wenlock turbidite sequence occupies inliers within the Midland Valley. The older greywackes contain abundant juvenile ophiolite and plutonic detritus in addition to a quartzofeldspathic metamorphic component; there are similarities with the most northerly part of the Southern Uplands. From the late Ordovician, εNd values systematically decline so that early Llandovery Midland Valley greywackes are exclusively quartzo-feldspathic, derived from an ancient source indistinguishable in isotopic terms from that periodically supplying the Southern Uplands. In general the Llandovery Midland Valley provenance was significantly more mature than that contemporaneously supplying the Southern Uplands. Thereafter, the Midland Valley latest Llandovery and early Wenlock greywackes contain a higher proportion of a juvenile component, and by the early Wenlock, greywackes from the Midland Valley, Southern Uplands and Lake District terranes are similar in terms of εNd. A common provenance seems likely and suggests that by the mid-Silurian all three terrenes were in close proximity.

Type
Articles
Information
Geological Magazine , Volume 132 , Issue 5 , September 1995 , pp. 571 - 580
Copyright
Copyright © Cambridge University Press 1995

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

Anderson, T. B., & Oliver, G. J. H., 1986. The Orlock Bridge Fault: a major late Caledonian sinistral fault in the Southern Uplands terrane, British Isles. Transactions of the Royal Society of Edinburgh: Earth Sciences 77, 203–22.CrossRefGoogle Scholar
Barnes, R. P., Lintern, B. C., & Stone, P., 1989. Timing and regional implications of deformation in the Southern Uplands of Scotland. Journal of the Geological Society, London 146, 905–8.CrossRefGoogle Scholar
Bluck, B. J., 1983. Role of the Midland Valley of Scotland in the Caledonian orogeny. Transactions of the Royal Society of Edinburgh: Earth Sciences 74, 119–36.CrossRefGoogle Scholar
British Geological Survey. 1992. The Rhins of Galloway. Scotland Sheets 1 and 3 with parts of 7 and 4W. Solid geology. 1:50 000. Keyworth, Nottingham: British Geological Survey.Google Scholar
Colman-Sadd, S. P., Stone, P., Swinden, H. S., & Barnes, R. P., 1992. Parallel geological development in the Dunnage Zone of Newfoundland and the Lower Palaeozoic terranes of southern Scotland: an assessment. Transactions of the Royal Society of Edinburgh: Earth Sciences 83, 571–94.CrossRefGoogle Scholar
Cope, J. C. W., Ingham, J. K., & Rawson, P. F., 1992. Atlas of Palaeogeography and Lithofacies. Geological Society of London Memoir, no. 18.Google Scholar
Dallmeyer, R. D., 1988. Polyphase tectonothermal evolution of the Scandinavian Caledonides. In The Caledonian-Appalachian orogen (eds Harris, A. L. and Fettes, D. J.), pp. 365–79. Geological Society of London Special Publication no. 38.Google Scholar
Elders, C. F., 1987. The provenance of granite boulders in conglomerates of the northern and central belts of the Southern Uplands of Scotland. Journal of the Geological Society, London 144, 853–63.CrossRefGoogle Scholar
Evans, J. A., Stone, P., & Floyd, J. D., 1991. Isotopic characteristics of Ordovician greywacke provenance in the Southern Uplands of Scotland. In Developments in sedimentary provenance studies (eds Morton, A. C., Todd, S. P. and Haughton, P. D. W.), pp. 161–72. Geological Society of London Special Publication no. 57.Google Scholar
Faure, G., 1986. The principles of isotope geology. Second edition. New York: John Wiley and Sons.Google Scholar
Floyd, J. D., 1982. Stratigraphy of a flysch succession: the Ordovician of W Nithsdale, SW Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 73, 1–9.CrossRefGoogle Scholar
Floyd, J. D., 1994. The derivation and definition of the ‘Southern Upland Fault’: a review of the Midland Valley-Southern Uplands terrane boundary. Scottish Journal of Geology 30, 51–62.CrossRefGoogle Scholar
Floyd, J. D., & Rushton, A. W. A., 1993. Ashgill greywackes in the Southern Uplands: an extension of the Ordovician succession in the Northern Belt. Transactions of the Royal Society of Edinburgh: Earth Sciences 84, 79–85.CrossRefGoogle Scholar
Harland, W. B., & 5 Others. 1990. A geologic time scale 1989. Cambridge University Press.Google Scholar
Hughes, R. A., Cooper, A. H., & Stone, P., 1993. Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia. Geological Magazine 130, 621–29.CrossRefGoogle Scholar
Kelley, S., & Bluck, B. J., 1989. Detrital mineral ages from the Southern Uplands using 40Ar−39Ar laser probe. Journal of the Geological Society, London 146, 401–3.CrossRefGoogle Scholar
Kelling, G., 1962. The petrology and sedimentation of Upper Ordovician rocks in the Rhins of Galloway, south-west Scotland. Transactions of the Royal Society of Edinburgh 65, 107–37.CrossRefGoogle Scholar
Kelling, G., Davies, P., & Holroyd, J., 1987. Style, scale and significance of sand bodies in the Northern and Central belts, southwest Southern Uplands. Journal of the Geological Society, London 144, 787–805.CrossRefGoogle Scholar
Kneller, B. C., 1991. A foreland basin on the southern margin of Iapetus. Journal of the Geological Society, London 148, 207–10.CrossRefGoogle Scholar
Kneller, B. C., King, L. M., & Bell, A. M., 1993. Foreland basin development and tectonics on the northwest margin of eastern Avalonia. Geological Magazine 130, 691–7.CrossRefGoogle Scholar
Kneller, B. C., Scott, R. W., Soper, N. J., Johnson, E. W., & Allen, P. M., 1994. Lithostratigraphy of the Windermere Supergroup, Northern England. Geological Journal 29, 219–40.CrossRefGoogle Scholar
Leggett, J. K., 1980. The sedimentological evolution of a Lower Palaeozoic accretionary fore-arc in the Southern Uplands of Scotland. Sedimentology 27, 401–17.CrossRefGoogle Scholar
Leggett, J. K., McKerrow, W. S., & Eales, M. H., 1979. The Southern Uplands of Scotland: a Lower Palaeozoic accretionary prism. Journal of the Geological Society, London 136, 755–70.CrossRefGoogle Scholar
Loeschke, J., 1985. Geochemistry of acidic volcanic clasts in Silurian conglomerates of the Midland Valley of Scotland: implications on the Caledonian orogeny. Geologische Rundschau 74, 537–46.CrossRefGoogle Scholar
Longman, C. D., Bluck, B. J., & Van Breemen, O., 1979. Ordovician conglomerates and the evolution of the Midland Valley. Nature 280, 578–81.CrossRefGoogle Scholar
McCaffrey, W. D., 1994. Sm-Nd isotopic characteristics of sedimentary provenance: the Windermere Supergroup of NW England. Journal of the Geological Society, London 151, 1017–21.CrossRefGoogle Scholar
Merriman, R. J., & Roberts, B., 1990. Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: geochemical evidence of ensialic marginal basin volcanism. Geological Magazine 127, 259–71.CrossRefGoogle Scholar
Morris, J. H., 1987. The Northern Belt of the Longford-Down Inlier, Ireland and Southern Uplands, Scotland: an Ordovician back-arc basin. Journal of the Geological Society, London 144, 773–86.CrossRefGoogle Scholar
O’Nions, R. K., Hamilton, P. J., & Hooker, P. J., 1983. A Nd isotope investigation of sediments related to crustal development in the British Isles. Earth and Planetary Science Letters 63, 229–40.CrossRefGoogle Scholar
Soper, N. J., & Woodcock, N. H., 1990. Silurian collision and sediment dispersal patterns in southern Britain. Geological Magazine 127, 527–42.CrossRefGoogle Scholar
Stone, P., 1995. Geology of the Rhins of Galloway district. Memoir of the British Geological Survey, Sheets 1 and 3 (Scotland).Google Scholar
Stone, P., Floyd, J. D., Barnes, R. P., & Lintern, B. C., 1987. A sequential back-arc and foreland basin thrust duplex model for the Southern Uplands of Scotland. Journal of the Geological Society, London 144, 753–64.CrossRefGoogle Scholar
Stone, P., & 5 Others. 1991. Geochemistry characterises provenance in southern Scotland. Geology Today 7, 177–81.CrossRefGoogle Scholar
Stone, P., Green, P. M., Lintern, B. C., Simpson, P. R., & Plant, J. A., 1993. Regional geochemical variation across the Iapetus Suture Zone: tectonic implications. Scottish Journal of Geology 29, 113–21.CrossRefGoogle Scholar
Stone, P., & Smellie, J. L., 1988. Classical areas of British geology: the Ballantrae area: description of the solid geology of parts of 1:25 000 sheets NX08, 18 and 19. London: HMSO for British Geological Survey.Google Scholar
Styles, M. T., Stone, P., & Floyd, J. D., 1989. Arc detritus in the Southern Uplands: mineralogical characterization of a “missing” terrane. Journal of the Geological Society, London 146, 397–400.CrossRefGoogle Scholar
Thirlwall, M. F., 1988. Geochronology of late Caledonian magmatism in northern Britain. Journal of the Geological Society, London 145, 951–67.CrossRefGoogle Scholar
Thirlwall, M. F., & Bluck, B. J., 1984. Sr-Nd isotope and geochemical evidence that the Ballantrae “ophiolite”, SW Scotland, is polygenetic. In Ophiolites and oceanic lithosphere (eds Gass, I. G., Lippard, S. J. and Shelton, A. W.), pp. 215–30. Geological Society of London Special Publication no. 13.Google Scholar