Hostname: page-component-848d4c4894-hfldf Total loading time: 0 Render date: 2024-06-09T17:41:34.538Z Has data issue: false hasContentIssue false
  • English
  • Français

A new K—Ar age from uppermost Tremadoc rocks of north Wales

Published online by Cambridge University Press:  01 May 2009

B. P. Kokelaar ,
F. J. Fitch  and
P. J. Hooker
B. P. Kokelaar
Affiliation:
School of Environmental Sciences, Ulster Polytechnic, Shore Road, Newtownabbey, Co. Antrim BT37 0QB
F. J. Fitch
Affiliation:
Department of Geology, Birkbeck College, University of London, Malet Street, London WC1E 7HX
P. J. Hooker
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ
Get access Rights & Permissions [Opens in a new window]

Summary

New conventional K–Ar dating of virtually unaltered pargasite phenocrysts extracted from a metabasalt of the uppermost Tremadocian Rhobell Volcanic Group, cropping out near Dolgellau, Gwynedd, north Wales, yields an age of 508 ± 11 Ma. This result provides a valuable new time-scale calibration point although incompatible with some other versions of the radiometric time-scale for the Lower Palaeozoic which have indicated ages of less than 508 ± 11 Ma for the Tremadoc/Arenig boundary.

Type
Articles
Information
Geological Magazine , Volume 119 , Issue 2 , March 1982 , pp. 207 - 211
Copyright
Copyright © Cambridge University Press 1982

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

Armstrong, R. L. 1978. Pre-Cenozoic Phanerozoic time-scale–computer file of critical dates of new and in-progress decay constant revisions. In Contributions to the Geological Time Scale (ed. Cohee, G. V., Glaessner, M. F. and Hedberg, H. D.). Am. Ass. Petrol. Geol. Stud. Geol. 6, 73–91.Google Scholar
Beckinsale, R. D. & Rundle, C. C. 1980. K–Ar ages for amphibole separates from the Rhobell Volcanic Group (Upper Tremadocian) Harlech Dome, North Wales. Rep. Inst. Geol. Sci. No. 80–1, 9–11.Google Scholar
Churkin, M., Carter, C. & Johnson, B. R. 1977. Subdivisions of Ordovician and Silurian time scale using accumulation rates of graptolitic shales Geology 5, 452–6.2.0.CO;2>CrossRefGoogle Scholar
Cole, G. A. J. & Holland, T. 1980. Structure and stratigraphic relations of Rhobell Fawr Geol. Mag. 7, 447–52.CrossRefGoogle Scholar
Cowie, J. W., Rushton, A. W. A. & Stubblefield, C. J. 1972. A correlation of Cambrian rocks in the British Isles Spec. Rep. Geol. Soc. Lond. 2, 1–42.Google Scholar
Cox, A. H. & Wells, A. K. 1927. The geology of the Dolgelley district, Merionethshire Proc. Geol. Ass. 38, 265–318.CrossRefGoogle Scholar
Dallmeyer, R. D. 1977. Diachronous ophiolite obduction in western Newfoundland; evidence from 40Ar–39Ar ages of the Hare Bay metamorphic aureole. Am. J. Sci. 277, 61–72.CrossRefGoogle Scholar
Fearnsides, W. G. 1905. On the geology of Arenig Fawr and Moel Llyfnant. Q. Jl geol. Soc. Lond. 61, 608–40.CrossRefGoogle Scholar
Fearnsides, W. G. 1910. The Tremadoc Slates and associated rocks of South East Caernarvonshire. Q. Jlgeol. Soc. Lond. 66, 142–88.CrossRefGoogle Scholar
Fitch, F. J., Forster, S. C. & Miller, J. A. 1974. Geological time scale. Rep. Prog. Phys. 37, 1433–96.CrossRefGoogle Scholar
Fitch, F. J., Forster, S. C. & Miller, J. A. 1976. The dating of the Ordovician. In The Ordovician System (ed. Bassett, M. G.), pp. 15–27. University of Wales Press and National Museum of Wales.Google Scholar
Gale, N. H., Beekinsale, R. D. & Wadge, A. J. 1979. A Rb–Sr whole rock isochron for the Stockdale Rhyolite of the English Lake District and a revised mid-Palaeozoic time-scale. J. geol. Soc. Lond. 136, 235–42.CrossRefGoogle Scholar
Gale, N. H., Beekinsale, R. D. & Wadge, A. J. 1980. Discussion of a paper by McKerrow, Lambert and Chamberlain on the Ordovician, Silurian and Devonian time scales. Earth Planet. Sci. Lett. 51, 9–17.CrossRefGoogle Scholar
Grasty, R. L. & Miller, J. A. 1965. The omegatron, a useful tool for argon isotope studies. Nature, Lond. 207, 1146–8.CrossRefGoogle Scholar
Hart, S. R., Davies, G. L., Steiger, R. H. & Tilton, G. R. 1968. A comparison of the isotopic mineral age variations and petrologic changes induced by contact metamorphism. In Radiometric Datin for Geologists (ed. Hamilton, E. I. and Farquhar, R. M.), pp. 73–110. New York: John Wiley & Sons.Google Scholar
Henningsmoen, G. 1973. The Cambro-Ordovician boundary. Lethaia 6, 423–39.CrossRefGoogle Scholar
Holmes, A. 1959. A revised geological time scale. Trans. Edinb. geol. Soc. 17, 183–216.CrossRefGoogle Scholar
Institute of Geological Sciences. 1981. Harlech Sheet 135 and part of Barmouth sheet 149. 1:50,000 series. Provisional Drift Edition.Google Scholar
Jacobsen, S. B. & Wasserburg, G. J. 1979. Nd and Sr isotopic composition of ocean crust and mantle and the evolution of the source of mid-ocean ridge basalts. J. Geophys. Res. 84, 7429–45.CrossRefGoogle Scholar
Kokelaar, B. P. 1979. Tremadoc to Llanvirn volcanism on the southeast side of the Harlech Dome (Rhobell Fawr), North Wales. In Caledonides of the British Isles – reviewed (ed. Harris, A. L., Holland, C. H. and Leake, B. E.), Geol. Soc. Lond., Spec. Publ. No. 8, 591–6.Google Scholar
Lambert, R. St J. 1971. The pre-Pleistocene Phanerozoic time-scale – a review. In The Phanerozoic Time-Scale; a supplement, Geol. Soc. Lond., Spec. Publ. 5, 9–31.CrossRefGoogle Scholar
Lambert, R. St J. & McKerrow, W. S. 1976. The Grampian Orogeny. Scott. J. Geol. 12, 271–92.CrossRefGoogle Scholar
Lanphere, M. A., Churkin, M. & Eberlein, G. D. 1977. Radiometric age of the Monograptus cyphus Zone in southeastern Alaska – an estimate of the Ordovician–Silurian boundary. Geol. Mag. 114, 15–24.CrossRefGoogle Scholar
Lynas, B. D. T. 1973. The Cambrian and Ordovician rocks of the Migneint area, North Wales. J. geol. Soc. Lond. 129, 481–503.CrossRefGoogle Scholar
McKerrow, W. S., Lambert, R. St J. & Chamberlain, V. E. 1980. The Ordovician, Silurian and Devonian time scales. Earth Planet. Sci. Lett. 51, 1–8.CrossRefGoogle Scholar
Miller, J. A. & Brown, P. E. 1964. How old is Scotland? Adv. Sci. 20, 527–39.Google Scholar
Roberts, B. 1981. Low grade and very low grade regional metabasic Ordovician rocks of Llŷn and Snowdonia, Gwynedd, North Wales. Geol. Mag. 118, 189–200.CrossRefGoogle Scholar
Ross, R. J., Naeser, C. W., Izett, G. A., Whittington, H. B., Hughes, C. P., Rickards, R. B., Zalasiewicz, J., Sheldon, P. R., Jenkins, C. J., Cocks, L. R. M., Bassett, M. G., Toghill, P., Dean, W. T. & Ingham, J. K. 1977. Fission-track dating of Lower Palaeozoic bentonites in British strato-types. Program and Abstr. 3rd Int. Symp. on Ordovician Syst. (Columbus: Ohio State University.)Google Scholar
Ross, R. J. Jr., Naeser, C. W., Izett, G. A., Whittington, H. B., Hughes, C. P., Rickards, R. B., Zalasiewicz, J., Sheldon, P. R., Jenkins, C. J., Cocks, L. R. M., Bassett, M. G., Toghill, P., Dean, W. T. & Ingham, J. K. 1978. Fission-track dating of Lower Palaeozoic volcanic ashes in British strato-types. Short Papers of the Fourth International Conference on Geochronology, Cosmochronology, Isotope Geology. In U.S. Geological Survey Open-File Report 78–701 (ed. Zartman, R. E.), 363–5.Google Scholar
Ross, R. J., Naeser, C. W., Izett, G. A., Obradovich, J., Bassett, M. G., Hughes, C. P., Cocks, L. R. M., Dean, W. T., Ingham, J. K., Jenkins, C. J., Rickards, R. B., Sheldon, P. R., Toghill, P., Whittington, H. B. & Zalasiewicz, J. 1982. Fission track dating of British Ordovician and Silurian stratotypes. Geol. Mag. 119, 135–53.CrossRefGoogle Scholar
Rundle, C. C. 1981. The significance of isotopic dates from the English Lake District for the Ordovician–Silurian time-scale. J. geol. Soc. Lond. 138, 569–72.CrossRefGoogle Scholar
Steiger, R. H. & Jäger, E. 1977. Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth Planet. Sci. Lett. 36, 359–62.CrossRefGoogle Scholar
Vidal, P., Auvray, B., Chariot, R., Fediuk, F., Haeurt, J. & Waldhausrova, J. 1975. Radiometric age of volcanics of the Cambrian ‘Krivoklat-Rokycany’ complex (Bohemian Massif). Geol. Rundsch. 64, 563–71.CrossRefGoogle Scholar
Wells, A. K. 1925. The geology of the Rhobell Fawr district (Merioneth). Q. J. geol. Soc. Lond. 81, 463–538.CrossRefGoogle Scholar