Metasomatic Interaction of Ultramafic Mantle Xenoliths with their Felsic HP–UHT Granulite Host (Moldanubian Domain, Bohemian Massif in Lower Austria).

This article focuses on the metasomatic interaction between mantle xenoliths and their host felsic granulite in the St. Leonhard granulite massif, Lower Austria, occurring at pressures of 1.0–1.2 GPa and temperatures of 900–1000°C. The study documents how chemical exchange—primarily the migration of Ca, Mg, and Al from garnet clinopyroxenite xenoliths to the granulite and K and Na in the opposite direction—led to the breakdown of clinopyroxene and formation of orthopyroxene–plagioclase symplectite coronae around the xenoliths, as well as a K-feldspar-poor zone in the host granulite. Diffusion chronometry constrains corona growth and subsequent rapid cooling over 13 to 532 thousand years, reflecting fast exhumation typical of the Variscan orogeny. The findings suggest that such crust–mantle chemical interactions may significantly influence the mineralogy, composition, and thermal structure of orogenic lower crust, particularly in hot collisional settings like the European Variscides.