The Fe-Ti oxides may not record shifts in magmatic conditions as quickly as we thought.
A series of experiments on dacite magma with a large single-step reduction show that even after two weeks, titanomagnetite and hemoilmenite crystals display disequilibrium textures and compositions.
Titanomagnetite morphology in starting materials versus experiments (2 log units fO2 lower than starting materials)
Major-element composition of Fe-Ti oxides, showing high Ti in the titanomagnetite rims and in the furthest-reacted hemoilmenite grains
End-member compositions of experimental run products, expected to fall on the dark green line, have generally progressed too far from input compositions (hemoilmenite) or else not far enough (titanomagnetite).
Publication: First, E., Hammer, J. Re-equilibration of Fe-Ti oxides: Textural and compositional effects of low fO2. American Mineralogist, in prep.