<sup>40</sup>Ar-<sup>39</sup>Ar Incremental Heating Studies on a Suite of 'Disturbed' Rocks from Cape Breton Island, Canada; Detection of a Deformational Episode

Authors

  • Ajoy K. Baksi
     National Geophysical Research Institute, Hyderabad 500 007

Abstract

40Ar_39Ar incremental heating studies have been carried out on a set of Middle Cambrian (age) whole-rock samples, which, in an earlier study (Hayatsu and Carmichael, 1970), yielded a K-Ar isochron age of ∼400 Ma and an initial 40Ar_39Ar ratio of ∼500. Age spectrum plots reveal that almost all of the argon originates from fine-grained K-feldspar and plagioclase in these rocks; the argon clock in these minerals was almost totally reset by a deformational event (part of the Acadian Orogeny) which occurred ∼400 Ma ago. Plotting the results on an Isochron diagram suggests that the high initial argon ratios noted earlier are not due to isotopic homogenisation on a grainsize scale. Since feldspars are known to be susceptible to argon loss at temperatures of >250°C, mild deformation and/or metamorphism in suitable rocks can now be identified and dated by careful 40Ar_39Ar incremental heating work.

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Issue

Volume 23, Issue 6, June 1982

Section

Research Papers

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Published

1982-06-01

How to Cite

Baksi, A. K. (1982). <sup>40</sup>Ar-<sup>39</sup>Ar Incremental Heating Studies on a Suite of ’Disturbed’ Rocks from Cape Breton Island, Canada; Detection of a Deformational Episode. Journal of Geological Society of India, 23(6), 267–276. Retrieved from https://geosocindia.com/index.php/jgsi/article/view/65038

References

BAKSI. A. K, (1973a) Quantitative unspiked argon runs in K-Ar dating. Can. Jour. Earth Sci., v. 10, pp. 1415-1419 .

BAKSI. A. K. (1973b) K-Ar dating: loading techniques in argon extraction work and source of. ail' argcn contamination. Can. Jour. Earth Sci., v. 10, pp. 1678-1684.

BAKSI. A. K. (1974a) Isotopic fractionation of a loosely held atmospheric argon argon component in the Picture Gorge Basalts. Earth Planet. Sci. Lett, v. 21, pp. 431-438.

BAKSI. A. K. (1974b) K-Ar study of the S. P. Flow. Can. Jour. Earth Sci., v. 11, pp. 1350-1356.

BAKSI. A. K. (1981) 40Ar_39Ar stepwise heating study of the Tudor Gabbro, Grenville Province,

Ontario; its bearing on the North American APW path in Late Proterozoic times. Submitted to Geophys. Jour. R.A.S.

BAKSI, A. K, and WILSON, A. F., (1980) An attempt at argon dating of two granulite facies terranes, Chem. Geol., v. 30, pp. 109-120.

BERGER, G. W., (1975) 4oAr/39Ar step heating of thermally overprinted biotite, hornblende and potassium feldspar from Eldora, Colorado. Earth Planet. Sci. Lett., v. 26, pp. 387-408.

BERGER, G. W. and YORK, D., (1981a) 40Ar_39Ar dating of the Thanet Gabbro; looking through , the Grenvillian metamorphic veil and implications for paleomagnetism. Can. Jour. Earth Sci,. v. 18, pp. 266-273,

BERGER, G. W. and YORK, D., (1981b) Geothermometry from 40Ar_39Ar dating experiments. Geochim. Cosmochim_ Acta, v. 45, pp. 795-811.

BERGER, G. W., YORK, D. and DUNLOP, D. J., (1979) Calibration of GrenviIIian paleopoles by 40Ar/39Ar dating. Nature, v. 277, pp. 46-48.

BOTTOMLEY, R. J. and YORK, D., (1976) 40Ar_39Ar age determination on the Owyhee Basalt of the Columbia Plateau. Earth Planet. Sci. Lett., v. 31, pp. 75-84.

COSTA, V., FERREIRA, M. P, MACEDO, R. and REYNOLDS, J. H., (1975) Rare gas dating-I; a demountable metal system with low blanks, Earth Planet. Sci. Lett., v. 25, pp. 131-141.

DALRYMPLE, G. B. and LANPHERE, M. A., (1971) 40Ar_39Ar technique of K-Ar dating; a: comparison with the conventional technique. Earth Planet Sci. Lett., v. 12, pp. 300-308.

DALRYMPLE, G. B. and LANPHERE, M. A., (1974) 40Ar_39Ar age spectra of some undisturbed terrestrial samples. Geochim. Cosmochim. ACla, v. 38, pp. 715-738.

FARRAR, E., McINTYRE, R. M" YORK, D. and KENYON, W. J., (964) A simple mass spectrometer for the analyses of argon at ultra-high vacuum. Nature, v. 204, pp. 531-533.

HALLlDAY, A. N., (1978) 40Ar_39Ar step heating studies of clay concentrates from Irish orebodies.

Geochim. Cosmochim. Acta. v. 42, pp. 1851-1858, '

HANSON, G. N., SIMMONS, K. R. and BENCE, A. E., (1975) 40Ar_39Ar spectrum ages for biotite.

hornblende and muscovite in a contact metamorphic zone. Geochim. Cosmochim. Acta, v. 39, pp. 1269-1277.

HAYATSU, A. and CARMICHAEl., C. M., (1970) K-Ar isochron method and initial argon ratios. Earth Planet. Sci. Lett. v. 8, pp, 71-76.

HAYATSU, A. and CARMICHAEl., C. M., (1977) Removal of atmospheric argon contamination and use and misuse of the K-Ar isochron method. Can. Jour. Earth Sci., v. 14, pp. 337-345.

HAYATSU. A. and PALMER, H. C., (1975). K-Ar isochron study of the Tudor Gabbro, Grenville Province, Ontario. Earth Planet. Sci. Lett., v. 25, pp. 208-212.

HUNEKE, J. C. and SMITH, S. P., (1976) The realities of recoil; 39Ar recoil in 40Ar-39Ar dating of lunar samples. Proc. Seventh Lunar Sci. Conf. Geochim. Cosmochim. Acta Suppl .. v. 7, pp. 1997-2008.

HUTCHINSON, R. D., (1952) The stratigraphy and trilobite fauna of the Cambrian sedimentary rocks of Cape Breton island, Nova Scotia. Geol. Surv. Canada, Mem. No. 263, p. 72.

LANPHERE, M. A. and DALRYMPLE, G. B., (1971) A test of the 40Ar_39Ar age spectrum technique on some terrestrial materials. Earlh Planet. Sci. Lett., v. 12, pp. 359-372.

McDOUGALL, I., (1974) The 40Ar/39Ar method of K-Ar age derermination of rocks using the HIFAR Reactor. Atomic Energy in Australia, v. 17, pp. 3-14.

MALUSKI, H., (1978) Behaviour of biotites, amphiboles, plagioclase and K-feJdspars in response to tectonic events with 4oAr_39Ar radiometric methods. Example of Corsican granite. Geochim. Cosmochim. Acta, v. 42, pp. 1619-1634.

MATE EN, A. and GREEN, D. C ,(1974) An assessment of irradiation parameters for 40Arf39Ar age determinations in HIFAR Reactor, Australia. Proc. Roy. Soc. Qld., v. 85, pp. 85-93.

MERRIHUE, C. and TURNER, G., (1966) Potassium-Argon dating by activation with fact neutrons. Jour. Geophys. Res .. v. 71, pp. 2852-2857.

NORTH, F. K., (1971) The Cambrian of Canada and Alaska. In: Cambrian of the New World (C. E. Holland, Ed.) John Wiley & Sons Ltd., London, pp. 219-324.

PAJARI, G. E., TREMBATH, L. T., CORMEIR, R. F. and FYFFE, L. R., (1974) The age of the Acadian deformation in southwestern New Brunswick. Can. Jour. Earlh Sci ., v. 11. pp. 1309-1313.

REYNOLDS, P. H. and MUECKE, G. E . (1978) Age studies on slates; applicability of the 40Ar_39Ar stepwise degassing method. Earth Planet. Sci. Lett., v. 40, pp. 111-118.

RODDICK, J. C., (1978) The application of isochron diagrams in 40Ar_39Ar dating. Earth Planet. Sci. Lett., v. 41, pp. 233-244.

SEIOEMANN, D., (1978) 40Ar_39Ar studies of deep-sea igneous rocks. Geochim. Cosmochim. Acta, v. 42, pp, 1721-1734.

SIGURGEIRSSON, T., (1962) Dating recent basalt by the potassium-argon method (In Icelandic). Rept. Phys. Lan. Iceland, 9p.

STEIGER, R. H. and JaGER, E., (1977) Subcommission on geochronology; Convention on the use of decay constants in geo- and cosmo-chronology. Earth Planet. Sci. Lett., v. 36, pp. 359-362.

TURNER, G. and CADOGAN, P. R., (1974) Possible effects of 39Ar recoil in 40Ar/39Ar dating of lunar samples. Proc. Fifth Lunar Sci. Conf. Geochim. Cosmochim. Acta, Suppl., v. 5, pp. 1601-1615.

TUREKTAN, K. K., (1976) Chemistry of the Earth. Holt, Rinehart and Winston Inc., New York, p.76.