Published online by Cambridge University Press: 05 July 2018
Textural relationships shown by oxide phases in olivine melilitites from Namaqualand-Bushmanland, South Africa, indicate early crystallization of picroilmenite from a relatively reduced magma. Evolution of a CO2-rich vapour during magma ascent led to an increase in oxygen activity and liquidus temperatures, causing rapid crystallization of titanomagnetite. Higher oxygen activities, together with the increase in calcium activity following CO2 loss from the magma, resulted in perovskite replacing ilmenite as the stable Ti phase.
Present address: Falconbridge Explorations (Botswana), PO Box 1463; Gaborone, Botswana.