Hostname: page-component-586b7cd67f-t8hqh Total loading time: 0 Render date: 2024-11-29T16:58:25.408Z Has data issue: false hasContentIssue false
  • English
  • Français

Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland

Published online by Cambridge University Press:  01 May 2009

Peter Mohr
Peter Mohr
Affiliation:
Department of Geology, University College, Belfield, Dublin 4, Ireland
Get access Rights & Permissions [Opens in a new window]

Abstract

Rb–Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464±26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and TDM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.

Type
Articles
Information
Geological Magazine , Volume 128 , Issue 3 , May 1991 , pp. 251 - 256
Copyright
Copyright © Cambridge University Press 1991

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

Barnes, C. G., Allen, C. M. & Brigham, R. H. 1987. Isotopic heterogeneity in a tilted plutonic system, Klamath Mountains, California. Geology 15, 523–7.2.0.CO;2>CrossRefGoogle Scholar
Brindley, J. C. 1954. The geology of the northern end of the Leinster Granite: Part 1 – internal structural features. Proceedings of the Royal Irish Academy 56B, 159–90.Google Scholar
Brindley, J. C. 1973. The structural setting of the Leinster Granite, Ireland - a review. Scientific Proceedings of the Royal Dublin Society 5A, 27–36.Google Scholar
Brooks, C., Hart, S. R. & Wendt, I. 1972. Realistic use of two-error regression treatments as applied to rubidium-strontium data. Reviews of Geophysics and Space Physics 10, 551–77.Google Scholar
Brown, P. E., Miller, J. A. & Grasty, R. L. 1968. Isotopic ages of late Caledonian granitic intrusions in the British Isles. Proceedings of the Yorkshire Geological Society 36, 251–76.Google Scholar
Brück, P. M. 1968. The geology of the Leinster Granite in the Enniskerry–Lough Dan area, Co. Wicklow. Proceedings of the Royal Irish Academy 66B, 53–70.Google Scholar
Brück, P. M. 1974. Granite varieties and structures of the Northern and Upper Liffey Valley Units of the Leinster Batholith. Geological Survey of Ireland Bulletin 1, 381–93.Google Scholar
Brück, P. M. 1975. A map and outline description of the Lower Palaeozoic rocks of SW Wicklow and S Kildare (one-inch sheets 128 and 129). Geological Survey of Ireland Report Series RS 75/2 (Geology).Google Scholar
Brück, P.M. & O'Connor, P.J. 1977. The Leinster Batholith: Geology and geochemistry of the Northern Units. Geological Survey of Ireland Bulletin 2, 107–41.Google Scholar
Brück, P. M. & Reeves, T. J. 1983. The geology of the Lugnaquillia Pluton of the Leinster Batholith. Geological Survey of Ireland Bulletin 3, 97–106.Google Scholar
Compston, W. & Chappell, B. W. 1979. Sr-isotope evolution of granitoid source rocks. In The Earth: Its Origin, Structure and Evolution (ed. McElhinny, M. W.), pp. 377–426. Academic Press.Google Scholar
Cooper, M. A. & Brück, P. M. 1983. Tectonic relationships of the Leinster Granite, Ireland. Geological Journal 18, 351–60.Google 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.Google Scholar
Dempsey, C. S., Halliday, A. N. & Meighan, I. G. 1990. Combined Sm–Nd and Rb–Sr isotope systematics in the Donegal granitoids and their petrographic implications. Geological Magazine 127, 75–80.Google Scholar
DePaolo, D. M. 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic. Nature 291, 193–6.Google Scholar
Elsdon, R. & Kennan, P. S. 1979. Geochemistry of Irish granites. In The Caledonides of the British Isles – Reviewed (eds Harris, A. L., Holland, C. H. and Leake, B. E.), pp. 713–16. Special Publication of the Geological Society of London no. 8.Google Scholar
Faure, G., Bowman, J. R., Elliot, D. H. & Jones, L. M. 1974. Strontium isotope composition and petrogenesis of the Kirkpatrick Basalt, Queen Alexandra Range, Antarctica. Contributions to Mineralogy and Petrology 48, 153–69.CrossRefGoogle Scholar
Fehn, U. & Hahn-Weinheimer, P. 1974. Rb–Sr ages of two epizonal granites of the southern Schwarzwald, Germany. Journal of Geology 82, 514–19.Google Scholar
Flood, R. H. & Shaw, S. E. 1977. Two ‘S–Type’ granite suites with low initial 87Sr/86Sr ratios from the New England Batholith, Australia. Contributions to Mineralogy and Petrology 61, 163–73.CrossRefGoogle Scholar
Gray, C. M. 1984. An isotopic mixing model for the origin of granitic rocks in southeastern Australia. Earth and Planetary Science Letters 70, 47–60.Google Scholar
Halliday, A. N., Stephens, W. E., Hunter, R. H., Menzies, M. A., Dickin, A. P. & Hamilton, P. J. 1985. Isotopic and chemical constraints on the building of the deep Scottish lithosphere. Scottish Journal of Geology 21, 465–91.Google Scholar
Hampton, C. M. & Taylor, P. N. 1983. The age and nature of the basement of southern Britain: evidence from Sr and Pb isotopes in granites. Journal of the Geological Society of London 140, 499–509.Google Scholar
Harmon, R. S., Halliday, A. N., Clayburn, J. A. P. & Stephens, W. E. 1984. Chemical and isotopic systematics of the Caledonian intrusions of Scotland and northern England: a guide to magma source region and magma-crust interaction. Philosophical Transactions of the Royal Society of London 310A, 709–42.Google Scholar
Juteau, M., Michard, A., Zimmermann, J. L. & Albarede, F. 1984. Isotopic heterogeneities in the granitic intrusion of Mount Capanne (Elba Island, Italy) and dating concepts. Journal of Petrology 25, 532–45.Google Scholar
Kennan, P. S., Feely, M. & Mohr, P. 1987. The age of the Oughterard Granite, Connemara, Ireland. Geological Journal 22, 273–80.Google Scholar
Kulp, J. L., Long, L. E., Giffin, C. E., Mills, A. A., Lambert, R. ST-J., Giletti, B. J. & Webster, R. K. 1960. Potassium-argon and rubidium-strontium ages of some granites from Britain and Eire. Nature 185, 495–7.Google Scholar
Lambert, R. ST-J. & Mills, A. A. 1961. Some critical points for the Paleozoic time scale from the British Isles. Annals of the New York Academy of Science 91, 378–88.Google Scholar
Leggo, P. J., Tanner, P. W. G. & Leake, B. E. 1969. Isochron study of Donegal Granite and certain Dalradian rocks of Britain. In North Atlantic – Geology and continental drift (ed. Kay, M.), pp. 354–62. Memoirs of the American Association of Petroleum Geologists no. 12.Google Scholar
Lutz, T. M. & Srogi, L-A. 1986. Biased isochron ages resulting from subsolidus isotope exchange: a theoretical model and results. Chemical Geology 56, 63–71.Google Scholar
McCarthy, T. S. & Cawthorn, R. G. 1980. Changes in initial 87Sr/86Sr ratio during protracted fractionation in igneous complexes. Journal of Petrology 21, 245–64.Google Scholar
McCutcheon, S., Lutes, G., Gauthier, G. & Brooks, C. 1981. The Pokiok Batholith: A contaminated Acadian intrusion with an anomalous Rb/Sr age. Canadian Journal of Earth Sciences 18, 910–18.Google Scholar
Menuge, J. F. 1988. The petrogenesis of massif anorthosites: a Nd and Sr isotopic investigation of the Proterozoic of Rogaland/Vest-Agder, SW Norway. Contributions to Mineralogy and Petrology 98, 363–73.Google Scholar
O'Connor, P. J. & Brück, P. M. 1976. Strontium isotope ratios for some Caledonian igneous rocks from central Leinster, Ireland. Geological Survey of Ireland Bulletin 2, 69–77.Google Scholar
O'Connor, P. J. & Brück, P. M. 1978. Age and origin of the Leinster Granite. Journal of Earth Science of the Royal Dublin Society 1, 105–13.Google Scholar
O'Connor, P. J., Long, C. B., Kennan, P. S., Halliday, A. N., Max, M. D. & Roddick, J. C. 1982. Rb–Sr isochron study of the Thorr and Main Donegal Granites, Ireland. Geological Journal 17, 279–95.Google Scholar
O'Connor, P. J., Aftalion, M. & Kennan, P. S. 1989. Isotopic U–Pb ages of zircon and monazite from the Leinster Granite, southeast Ireland. Geological Magazine 126, 725–8.Google Scholar
Roddick, J. C. & Compston, W. 1977. Strontium isotopic equilibration: a solution to a paradox. Earth and Planetary Science Letters 34, 238–46.Google Scholar
Roycroft, P. D. 1989. Zoned muscovite from the Leinster Granite, S.E. Ireland. Mineralogical Magazine 53, 663–5.Google Scholar
Simonetti, A. & Doig, R. 1990. U–Pb and Rb–Sr geochronology of Acadian plutonism in the Dunnage zone of the southeastern Quebec Appalachians. Canadian Journal of Earth Sciences 21, 881–92.Google Scholar
Stephens, W. E. & Halliday, A. N. 1980. Discontinuities in the composition surface of a zoned pluton, Criffell, Scotland. Geological Society of America Bulletin 91, 165–70.Google Scholar
Sweetman, T. M. 1987. The geochemistry of the Blackstairs Unit of the Leinster Granite, Ireland. Journal of the Geological Society, London 144, 971–84.Google Scholar
Sweetman, T. M. 1988. The geology of the Blackstairs Unit of the Leinster Granite. Irish Journal of Earth Sciences 9, 39–59.Google Scholar
York, D. 1969. Least-squares fitting of a straight line with correlated errors. Earth and Planetary Science Letters 5, 320–4.Google Scholar
Zheng, Y. F. 1989. Influences of the nature of the initial Rb–Sr system on isochron validity. Chemical Geology (Isotope Geoscience Section) 80, 1–16.Google Scholar