Geochemical and age heterogeneity of titanites from the orthogneisses of Pon'gom Navolok Island

We studied the geochemical and age heterogeneity of titanites separated fro m tectonized orthogneiss at the contact between hypersthene diorites and am phibole granodiorites in Pon'gom Navolok Island, Belomorian Tectonic Zone. Titanite was formed at 1811.4 +/- 4.1 Ma during the final stage of dynamome tamorphism of the contact rocks. Titanites from the orthogneisses are chara cterized by reverse age discordance and contain zircon inclusions, which we re entrapped during crystallization and cause age overestimation. It was sh own that, during an early stage of Caledonian reactivation, reaction zones enriched in Si, Ti, and Fe and depleted in Ca, Al, and U were formed along the fissures and in the rims of titanite under the action of low-temperatur e hydrothermal fluid. This phenomenon resulted in the reverse age discordan ce of titanites. The methods allowing correct isotope dating of titanites a re considered.