Hydrothermal alteration of magmatic titanite: Evidence from Proterozoic granitic rocks, Southeastern Sweden

Magmatic titanite in Proterozoic granitic rocks from southeastern Sweden has been subjected to hydrothermal dissolution and replacement by finely crystalline Fe-dominant chlorite and TiO₂ (± quartz ± calcite). These alteration patterns require the redistribution of the highly immobile Ti and At on the thin-section scale. The chloritization of titanite involved the formation of an intermediate Al-Fe-rich phase probably comprising intimately intergrown, submicroscopic chlorite and titanite. The creation of microporosity by the hydrothermal alteration of titanite may enhance the diffusive flux of matter, and hence the rate of reactions in granitic rocks. The alteration of titanite is most pronounced in red-stained granitic rock zones enriched in partly dissolved biotite and magnetite, which could have acted as local source of Al, Fe and Mg needed for chlorite formation.