Coesite Discovery in Eclogites Confirms UHP Metamorphism in the Orlica‐Śnieżnik Dome (SW Poland)

ABSTRACT Eclogite lenses are exposed within the orthogneiss‐dominated core of the Orlica‐Śnieżnik Dome in the Sudetes, which forms the northeastern margin of the Bohemian Massif (Variscan Belt of Central Europe). The presence of coesite inclusions in garnet and omphacite confirms that these eclogites underwent ultrahigh‐pressure metamorphism. This interpretation is further supported by phase equilibria modelling, which indicates peak‐pressure metamorphic conditions of 2.9–3.2 GPa and 750°C–830°C. The results are consistent with estimates derived from conventional geothermobarometry and Zr‐in‐rutile thermometry applied to rutile inclusions in garnet. Based on quartz‐in‐garnet elastic barometry, a maximum entrapment pressure of approximately 2.0 GPa is obtained. We interpret this discrepancy as a result of viscous relaxation of garnet at high temperature. The first stage of re‐equilibration during decompression occurred at a pressure of 2.0–2.2 GPa and a temperature of 680°C–770°C. The observed rock associations exhibit similarities to other UHP occurrences within the Saxo‐Thuringian Zone, suggesting a comparable exhumation mechanism. This likely involved initial buoyancy‐driven exhumation within a subduction channel, followed by crustal‐scale folding. Furthermore, the maximum pressure recorded in the eclogites may partly reflect nonlithostatic components, such as transient pressure variations arising from rheological heterogeneity between the eclogites and their host rocks.