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The Metamorphism of the Pre-Cambrian Dolomites of Southern Eyre Peninsula, South Australia

Published online by Cambridge University Press:  01 May 2009

C. E. Tilley
C. E. Tilley
Affiliation:
Emmanuel College, Cambridge.
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Extract

THE rocks arising from the metamorphism of the more impure dolomitic sediments are calc-magnesian silicate types in which all carbon dioxide has been expelled. In some of the rocks to be described it is clear that superposed on the normal metamorphism there has been a metamorphism by addition of material from the neighbouring magma.

Type
Original Articles
Information
Geological Magazine , Volume 57 , Issue 11 , November 1920 , pp. 492 - 500
Copyright
Copyright © Cambridge University Press 1920

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References

page 494 note 1 Adams, F. D. and Barlow, A. E., Mem. Geol. Surv. Can., No. 6, 1910, p. 102.Google Scholar

page 496 note 1 Cordierite would appear to be an exception to this rule. Its absence in metamorphosed limestones is remarkable. A development in accordance with the equation

page 496 note 2 CaMg (CO3)2 + 2 H4Al2Si2O9 + SiO2 = (2MgO.2Al2O3.5SiO2) + 2CaCO3 + 2CO2 + 4H2O cordierite might be expected, but it would appear that the alumina is absorbed in anorthite, and diopside forms instead. CaMg (CO3)2 + CaCO3 + H4Al2Si2O9 + 2SiO2 = CaMg(SiO3)2 + CaAl2Si2O8 + 2H2O + 3CO2

page 497 note 1 Loc. cit. supra, p. 91.Google Scholar

page 497 note 2 Cf. Spurr, J. E., Econ. Geol., vol. vii, 1912, p. 455.Google Scholar This term would be embraced under V. M. Goldsehmidt's term “pneumatolytic contact metamorphism”.Google Scholar

page 498 note 1 Diopside microcline rocks have been described by Flett, J. S. (“The Geology of the country around Bodmin and St. Austell”: Mem. Geol. Surv., 1909, p. 100)Google Scholar, and by Bailey, E. B. (“The Geology of Ben Nevis and Glen Coe”: Mem. Geol. Surv., 1916, pp. 190–4)Google Scholar, and the associations in those cases would seem to demand the presence of an aluminous diopside as these investigators have suggested.

page 498 note 2 Borgström, L. H., Zeitschr. Kryst. Min., vol.liv, 1914, p. 238.Google Scholar

page 498 note 3 Sundius, N., Bull. Geol. Inst. Univ. Upsala, vol. xvi, 1919, pp. 96–106.Google Scholar