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Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar PH20

Published online by Cambridge University Press:  05 July 2018

R. N. Thompson
R. N. Thompson*
Affiliation:
Department of Geology, Imperial College of Science and Technology, London SW7 2BP
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Abstract

Experimental melting equilibria at 1 kbar PH2O are reported for three early Tertiary granites from Skye and one from Rhum, together with a quartz monzonite from Ardnamurchan. The Hebridean Province leucogranites show cotectic melting behaviour, whilst associated ‘primitive’ (mostly adamellitic) acid plutons have silicate liquidi ∼ 925 °C and plagioclase liquidi ∼ 875 °C. At such high temperatures the morefusible crustal rock types of the region would be almost completely molten. If the Tertiary ‘primitive’ acid magmas were simple crustal melts, they would inherit the incompatible element ratios of their sialic progenitors. This is demonstrably not so. Minor element ratios in these plutons are consistent with extensive fractional crystallization during the evolution of their magmas. But it is, in most individual instances, extremely difficult to specify, either by thermal or geochemical arguments, whether (1) fractional crystallization followed sialic contamination of basic magmas or (2) mixing occurred between fractionation residua and sialic melts. Both the minor element ratios and cotectic melting behaviour of the Hebridean Province leucogranites are consistent with the view that they are products of extreme fractional crystallization of (sial contaminated) more-basic magmas. Nevertheless, it is clear—when the sequence and timing of emplacement of acid magmas within individual intrusive centres is considered—that very complex polycyclic combinations of fusion, fractionation, and re-fusion were involved in the evolution of these granites.

The solidi of the samples studied experimentally, together with published data, show a progressive rise in temperature as the compositions of the rocks diverge from the minimum melting composition in NaAlSi3O8-KAlSi3O8-SiO2 at 1 kbarH2O. This relationship is important when considering the likely nature of sialic contamination of basic to intermediate continental magmatic suites fed through reservoir systems which are swarms of dykes and, or, sills. Because salic low-solidus crustal rock types also show near-cotectic melting behaviour, the composition of the contaminant may be strongly biased towards these (usually minor) crustal units, rather than the ‘bulk’ or average crustal composition.

Type
Research Article
Information
Mineralogical Magazine , Volume 47 , Issue 343 , June 1983 , pp. 111 - 121
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1983

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References

Ahern, J. L., Turcotte, D. L., and Oxburgh, E. R. (1981) J. Geol. 89, 421–32.CrossRefGoogle Scholar
Bell, J. D. (1976) Proc. Geol. Assoc. 87, 247–71.CrossRefGoogle Scholar
Brown, G. M. (1963) Mineral. Mag. 33, 533–62.Google Scholar
Carmichael, I. S. E., Turner, F. J., and Verhoogen, J. (1974) Igneous Petrology. St. Louis: McGraw-Hill Book Co. Google Scholar
Carter, S. R., Evensen, N. M., Hamilton, P. J., and O'Nions, R. K. (1978) Science, 202, 743–7.CrossRefGoogle ScholarPubMed
Dickin, A. P. (1981) J. Petrol. 22, 155–89.CrossRefGoogle Scholar
Dickin, A. P. and Exley, R. A. (1981) Contrib. Mineral. Petrol. 76, 98–108.CrossRefGoogle Scholar
Dunham, A. C. (1968) Q. J. Geol. Soc. Lond. 123, 327–52.CrossRefGoogle Scholar
Holland, J. G., and Brown, G. M. (1972) Contrib. Mineral. Petrol. 37, 139–60.CrossRefGoogle Scholar
James, R. S. and Hamilton, D. L. (1969) Ibid. 21, 111–41.Google Scholar
Meighan, I. G. (1979) Bull. Geol. Surv. G.B. 10–22.Google Scholar
Moorbath, S., Stewart, A. D., Lawson, D. E., and Williams, G. E. (1967) Scott. J. Geol. 3, 389–412.CrossRefGoogle Scholar
Moorbath, S., and Welke, H. (1969) Earth Planet Sci. Lett. 5, 217–30.CrossRefGoogle Scholar
O'Hara, M. J., and Mathews, R. E. (1981) J. Geol. Soc. Lond. 138, 237–77.CrossRefGoogle Scholar
Patchett, P. J. (1980) Nature, Lond. 283, 559–61.CrossRefGoogle Scholar
Pidgeon, R. T., and Aftalion, M. (1978) Geol. J. Spec. Issue, 10, 183–220.Google Scholar
Piwinskii, A. J. (1968) J. Geol. 76, 548–70.CrossRefGoogle Scholar
Piwinskii, A. J.and Wyllie, P. J. (1968) Ibid. 76, 205–34.Google Scholar
Streckeisen, A. L. (1973) Neues Jahrb. Mineral. Monat. 149–64.Google Scholar
Sun, S-S. (1980) Phil. Trans. R. Soc. Lond. A297, 409–45.Google Scholar
Thompson, R. N. (1965) D.Phil, thesis. University of Oxford.Google Scholar
Thompson, R. N. (1969) Q. J. Geol. Soc. Lond. 124, 349–85.CrossRefGoogle Scholar
Thompson, R. N. (1980) Geol. Rundsch. 69, 245–62.CrossRefGoogle Scholar
Thompson, R. N. (1981) Mineral. Mag. 44, 161–70.CrossRefGoogle Scholar
Thompson, R. N. (1982a) Scott. J. Geol. 18, 49–107.CrossRefGoogle Scholar
Thompson, R. N. (1982b) In Sutherland, D. S. (ed.), Igneous Rocks of the British Isles, John Wiley and Sons Ltd., 461–77.Google Scholar
Thompson, R. N., Dickin, A. P., Gibson, I. L., and Morrison, M. A. (1982) Contrib. Mineral. Petrol. 79, 159–68.CrossRefGoogle Scholar
Thompson, R. N. and MacKenzie, W. S. (1967) Am. J. Sci. 265, 714–34.CrossRefGoogle Scholar
Thorpe, R. S., Potts, P. J., and Sarre, M. B. (1977) Earth Planet Sci. Lett. 36, 111–20.CrossRefGoogle Scholar
Tuttle, O. F., and Bowen, N. L. (1958) Mem. Geol. Soc. Am. 74, 1–153.Google Scholar
Wager, L. R., Vincent, E. A., Brown, G. M., and Bell, J. D. (1965) Phil. Trans. R. Soc. Lond. A257, 273– 307.Google Scholar
Wager, L. R., Weedon, D. S., and Vincent, E. A. (1953) Mineral. Mag. 30, 263–76.Google Scholar
Walsh, J. N., Beckinsale, R. D., Skelhorn, R. R., and Thorpe, R. S. (1979) Ibid. 71, 99–116.Google Scholar
Walsh, J. N., and Clarke, E. (1982) Mineral. Mag. 45, 247–55.CrossRefGoogle Scholar
Walsh, J. N., and Henderson, P. (1977) Contrib. Mineral. Petrol. 60, 31–8.CrossRefGoogle Scholar
Weaver, B. L., and Tarney, J. (1980) Earth Planet Sci. Lett. 51, 279–96.CrossRefGoogle Scholar
Weaver, B. L., (1981) Ibid. 55, 171–80.Google Scholar
Weertman, J. (1971) J. Geophys. Res. 76, 1171–83.CrossRefGoogle Scholar
Wyllie, P. J., Huang, W-L, Stern, C. R., and Maatee, S. (1976) Canad. J. Earth Sci. 13, 1007–19.CrossRefGoogle Scholar