Abstract

This study investigates magnetite exsolution in ilmenite from Fe-Ti oxide gabbro in the Xinjie intrusion, SW China. Exsolved magnetite lamellae in ilmenite contain nearly pure Fe3O4 with ~1 wt% TiO2. EBSD-based analyses indicate that the magnetite lamellae have close-packed oxygen planes and directions parallel to those in the host ilmenite with {111}Mag//(0001)Ilm and <110>Mag//<101¯0>Ilm The Fe2+ in the magnetite lamellae is probably derived from adjacent titanomagnetite by sub-solidus inter-oxide cation repartitioning of Fe2+ + Ti4+ = 2Fe3+ during cooling. It is thus suggested that only Fe3+ cations in the magnetite lamellae should be included into the composition of the Ilm-Hemss precursor for the Fe-Ti oxide oxy-thermometer. The existence of magnetite exsolution in ilmenite also provides an alternative explanation for unusually strong natural remnant magnetization in natural ilmenite.

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