Hostname: page-component-586b7cd67f-2plfb Total loading time: 0 Render date: 2024-11-27T05:39:33.037Z Has data issue: false hasContentIssue false
  • English
  • Français

The iron-titanium oxides of some Dunedin (New Zealand) lavas, in relation to their palaeomagnetic and thermomagnetic character (with an appendix on associated chromiferous spinel)

Published online by Cambridge University Press:  14 March 2018

J. B. Wright
J. B. Wright*
Affiliation:
Geology Department, University of Otago, New Zealand1
Get access Rights & Permissions [Opens in a new window]

Summary

Earlier palaeomagnetic studies on the Dunedin volcano showed that a portion of the sequence is reversely or anomalously magnetized. Some of the rocks used for palaeomagnetic study were subsequently classified into groups according to their thermomagnetic behaviour (unpublished work).

Cell dimensions and Curie-point curves have been measured for oxides separated from representative rocks of each group. The oxides are mostly homogeneous titanomagnetites containing between 40 and 55 mol. % of ulvöspinel, with a generally small degree of late low-temperature alteration. X-ray and thermomagnetic data also suggest that there was some early oxidation to titanomaghemite, probably during cooling.

The thermomagnetic behaviour of rocks classified in the different groups is attributed to variable oxidation of the titanomagnetite during thermomagnetic treatment. The high Curie points of rocks used for palaeomagnetic studies may often be due merely to oxidation of titaniferous magnetite and not to nearly pure primary Fe3O4. Since there is insufficient oxidation in the lavas examined for any currently accepted self-reversal process to have been operative, the reversely magnetized part of the Dunedin sequence was probably erupted during a reversed polarity epoch, possibly between about 13 and 11 million years ago.

The basanitic lavas contain minor amounts of chromiferous spinel, as inclusions in silicate phenocrysts and as cores to separate microphyric titanomagnetite; its significance is briefly discussed.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 36 , Issue 279 , September 1967 , pp. 425 - 435
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1967

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

Ade-Hall, (J. M.), 1964. Geophys. Journ. Roy. Astron. Soc., vol. 8, pp. 403–423.CrossRefGoogle Scholar
Akimoto, (S.), Katsura, (T.), and Yoshida, (M.), 1957. Journ. Geomag. Geoelect., vol. 9, pp. 165–178.CrossRefGoogle Scholar
Aoki, (K.), 1966. Amer. Min., vol. 51, pp. 1799–1805.Google Scholar
Babkine, (J.), 1965. Bull. soc. franÇ. Min. Crist., vol. 88, pp. 306–318.Google Scholar
Babkine, (J.), Conquéré, (F.), Vilminet, (J.-C.), and Phan, (K. D.), 1965. Ibid., pp. 447-455.CrossRefGoogle Scholar
Coombs, (D. S.), 1965. New Zealand Dept. Sci. Indust. Res., Inform. Ser. 51 (Thompson, B. N., Kermode, L. O., ed.), pp. 54–67.Google Scholar
Coombs, (D. S.), and Hatherton, (T.), 1959. Nature, vol. 184, pp. 883–884.CrossRefGoogle Scholar
Coombs, (D. S.), White, (A. J. R.), and Hamilton, (D.), 1960. New Zealand Journ. Geol. Geophys., vol. 3, pp. 573–579.Google Scholar
Meitzner, (W.), 1963. Beitr. Min. Petr., vol. 9, pp. 320–352.CrossRefGoogle Scholar
O'Reilly, (W.) and Banerjee, (S. K.), 1966. Nature, vol. 211, pp. 26–28.CrossRefGoogle Scholar
Osborn, (E. F.) and Tait, (D. B.), 1952. Amer. Journ. Sci., Bowen vol., pp. 413–433.Google Scholar
Powell, (D. S.), 1963. Nature, vol. 199, pp. 674–676.CrossRefGoogle Scholar
Schreiter, (P.) and Vollstädt, (H.), 1964. Monatsberichte, deutsch. Akad. Wiss. Berlin, vol. 6, pp. 811–814.Google Scholar
Wilkinson, (J. F. G.), 1965. Min. Mag., vol. 34, pp. 528–541.Google Scholar
Wright, (J. B.) and Lovering, (J. F.), 1965. Min. Mag., vol. 35, pp. 604–621.Google Scholar
Wright, (J. B.) and Lovering, (J. F.), 1967. Geophys. Journ. Roy. Astron. Soc., in press.Google Scholar