A Method of Tracing the Temperature and Oxygen-Fugacity Histories of Complex Magnetite-Ilmenite Grains

John F. W. Bowles1
Department of Geology, University College, London EC1E 6BT
1Present address: Institute of Geological Sciences, 64-78 Gray's Inn Road, London WC1X 8NG.

Summary: The formation of ilmenite from titanomagnetite frequently shows separate generations of production. The ilmenite products can be combined with the magnetite host to represent the intermediate stages in this development. Use of the Buddington and Lindsley (1964) geothermometer in conjunction with this method provides a number of points in the temperature and oxygen-fugacity history of a single, complex magnetiteilmenite grain.

Application of the method is illustrated by an example from the Freetown layered gabbro. A titanomagnetite exsolved granular ilmenite whilst cooling and this process ceased at 930° and an oxygen fugacity of log ƒO2 = −11·5. Further cooling and exsolution continued until the grain reached 662 °C and log ƒO2 = −19·0, producing distinct ilmenite lamellae.

Mineralogical Magazine; March 1977 v. 41; no. 317; p. 103-109; DOI: 10.1180/minmag.1977.041.317.15
© 1977, The Mineralogical Society
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