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New Rb–Sr and U–Pb ages for the Carnsore Granite and their bearing on the antiquity of the Rosslare Complex, southeastern Ireland

Published online by Cambridge University Press:  01 May 2009

P. J. O'Connor ,
P. S. Kennan  and
M. Aftalion
P. J. O'Connor
Affiliation:
Geological Survey of Ireland, Beggars Bush, Haddington Road, Dublin 4, Ireland
P. S. Kennan
Affiliation:
Department of Geology, University College, Belfield, Dublin 4, Ireland
M. Aftalion
Affiliation:
Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 OQU, UK
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Abstract

A 12-point whole-rock Rb–Sr isochron for the Carnsore Granite of southeastern Ireland yields an age of 428±11 Ma and initial 87Sr/86Sr ratio of 0.7068±0.0003 (index of goodness of fit, MSWD = 0.65). A similar mean 207Pb/206Pb age of 432±3 Ma from three slightly discordant zircon size fractions from the granite is also indicated, and shows that the pluton was emplaced contemporaneously with the neighbouring Saltee Granite.

Thus, Tuskar Group rocks, which are intruded by the Carnsore Granite, could be as young as Ordovician. While the early history of the Rosslare Complex is undoubtedly Precambrian, the new age for the Carnsore pluton means that the later intrusive and tectonothermal events in the history of this complex are no longer constrained to be Precambrian and may have occurred over a 150 + Ma interval in Cambro-Ordovician time.

The zircons from the Carnsore Granite are slightly discordant, and show no apparent inherited radiogenic lead component. The initial 87Sr/86Sr ratio suggests that the magma may have been derived as a melt in the lower crust. The higher strontium isotope ratios of the Rosslare gneisses would seem to preclude their involvement in the genesis of the Carnsore magma.

Type
Articles
Information
Geological Magazine , Volume 125 , Issue 1 , January 1988 , pp. 25 - 29
Copyright
Copyright © Cambridge University Press 1988

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References

Baker, J. W. 1966. The Ordovician and other post-Rosslare Series rocks in southeast Co. Wexford. Geological Journal 5, 1–6.CrossRefGoogle Scholar
Baker, J. W. 1968. The petrology of the Carnsore Granite intrusion, Co. Wexford. Proceedings of the Royal Irish Academy 67B, 159–76.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, 551–7.CrossRefGoogle Scholar
Crimes, T. P. & Dhonau, N. B. 1967. The Pre-Cambrian and Lower Palaeozoic rocks of southeast Co. Wexford, Eire. Geological Magazine 104, 213–21 and 400.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.Google Scholar
Jaffey, A. H., Flynn, K. F., Glendenin, L. E., Bentley, W. C. & Essling, A. M. 1971. Precision measurements of half-lives and specific activities of 235U and 238U. Physics Review C 4, 1889–1906.CrossRefGoogle Scholar
Krogh, T. E. 1973. A low-contmination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determination. Geochimica et Cosmochimica Acta 37, 485–94.CrossRefGoogle Scholar
Leutwein, F., Sonet, J. & Max, M. D. 1972. The age of the Carnsore Granodiorite. Geological Survey of Ireland Bulletin 1, 303–9.Google Scholar
Max, M. D. 1975. Precambrian rocks of south-east Ireland. In A correlation of the Precambrian rocks in the British Isles (eds. Harris, A. L. et al. ), pp. 97–101. Geological Society of London Special Report no. 6.Google Scholar
Max, M. D. & Dhonau, N. B. 1971. A new look at the Rosslare Complex. Scientific Proceedings of the Royal Dublin Society 5A, 103–20.Google Scholar
Max, M. D. & Long, C. B. 1985. Pre-Caledonian basement in Ireland and its cover relationships. Geological Journal 20, 341–66.Google Scholar
Max, M. D. & Ryan, P. D. 1986. The Tuskar Group of southeastern Ireland: its geochemistry and depositional provenance. Proceedings of the Geologists' Association 97, 73–9.CrossRefGoogle Scholar
Max, M. D., Ploquin, A. & Sonet, J. 1979. The age of the Saltees granite in the Rosslare Complex. In The Caledonides of the British Isles – reviewed (eds. Harris, A. L. et al. ), pp. 723–5. Scottish Academic Press.Google Scholar
O'Connor, P. J. 1974. Origin of the Carnsore Granodiorite. Geological Survey of Ireland Bulletin 1, 471–5.Google Scholar
O'Connor, P. J. & Brück, P. M. 1978. Age and origin of the Leinster granite. Journal of Earth Sciences of the Royal Dublin Society 1, 105–13.Google Scholar
O'Connor, P. J. & Reeves, T. J. 1979. Age and provenance of the Carrigmore diorite, Co. Wicklow. Geological Survey of Ireland Bulletin 2, 307–14.Google Scholar
Treloar, P. J. & Max, M. D. 1984. The hornfels and depth of emplacement of the Carnsore Granite, southeast Ireland. Proceedings of the Geologists' Association 95, 185–90.Google Scholar
York, D. 1969. Least squares fitting of a straight line with correlated errors. Earth and Planetary Science Letters 5, 320–4.CrossRefGoogle Scholar