Magnesian Ilmenite in Picritic Basalts from the Karoo Province, South Africa

R. Grant Cawthorn, John W. Bristow and David I. Groves
Geology Department, University of the Witwatersrand, Wits, 2050, South Africa
Geology Department, De Beers Consolidated Mines, Box 47, Kimberley, 8300, South Africa
Geology Department, University of Western Australia, Nedlands, 6009, Australia

Abstract: Some picritic lavas from near the base of the volcanic succession in the Lebombo region of the Karoo Province contain phenocrysts of olivine and skeletal microphenocrysts of ilmenite, the latter indicating rapid crystallization from the magma. These ilmenite grains contain up to 6% MgO. The near-liquidus crystallization and the high MgO content of the ilmenite are highly anomalous for ilmenite in tholeiitic rocks. These features reflect the atypical nature (high MgO and TiO2) of the parental magma and/or highly reduced conditions of crystallization.

Keywords: magnesian ilmenite • ilmenite • basalts • Karoo Province • South Africa

Mineralogical Magazine; April 1989 v. 53; no. 370; p. 245-252; DOI: 10.1180/minmag.1989.053.370.12
© 1989, The Mineralogical Society
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