Lamellae of baddeleyite and Fe-Cr-spinel in ilmenite from the Basistoppen Sill, East Greenland

Ilnenite inthe Gabbro Picrite Zone of the Basistoppen rill, Ea$t Greenland, contain; exsolution lamellae of bad&leyite and Fe-Cr*pinel. The relative proportions of baddeleyite and Fe-Cr-spinel in isolated ilmenite grains indicate that the ilmenite was reduced during zubsolidus re-equilibration, although the sill in general was oxidized during cooling. Calculated pre-exsolutioncompositions for the ilrnenite contain up1o2.4Vo Cr2O3 and up to 7100ppm Zr. The calsulated Zr-content is higher than tlat of any previously reportd lgnar or terrctrid ilmenite. The reduction-exsolution of Fe-Cr*pinel is considered the result of the incorporatiou of Cr in the ilmenite dudng crystallization at concentrations that exceeded the solubility limit of Cr in ilmenite at the temperatures of re-equitbration. The Zr content of the host ilnenite is well below the solubility limit of Zr in ilmenite, indicating that oversaturation was not ttre driving force for the exsolution ofbaddeleyite. The exsolution of baddeleyite in tle ilmenite may have partly compensated fortle overallreduction of tle ilmenite resulting from the exsolution of Fe-Cr-spinel.