P‐T‐t‐d Evolution of Low‐Grade Metamorphic Xenotime, Eastern Alps (Austria)

ABSTRACT In situ LA‐ICP‐MS U‐Pb dating of xenotime was used to establish the age of low‐grade metamorphism in Permian metasediments of the Austroalpine Unit (Eastern Alps, Austria). Complexly zoned xenotime in chloritoid‐bearing metasedimentary samples possesses distinct MREE‐rich domains. In the eastern sample, this domain yielded a date of c. 135 Ma, which we interpret as the age of peak metamorphism at 350°C and 0.4–0.5 GPa based on host‐inclusion relationships between chloritoid and xenotime. In the western sample, MREE‐rich xenotime formed at c. 92 Ma related to the formation of a pervasive crenulation cleavage post‐dating the metamorphic peak. In both samples, metamorphic xenotime formed paragenetically with florencite and apatite at the expense of detrital xenotime and REE‐bearing apatite, and is linked to deformation facilitated by dissolution‐precipitation. This study demonstrates that coupling in situ xenotime dating with comprehensive microstructural and chemical characterisation is a promising strategy to determine precise tectono‐metamorphic events in low‐grade metamorphic units.