Records of mantle-crust exchange processes during continental subduction-exhumation in the Nonsberg-Ultental garnet peridotites (Eastern Alps)

In the Nonsberg-Ultental area (Tonale nappe), Grt-bearing peridotites occur in high-P migmatitic gneisses enclosing relics of eclogites. The peridotites record the transformation of high-T Spl-lherzolites to coronitic Grt+Spllherzolites to fine-grained Amph±Grt-peridotites. The transformation is preceeded by LILE enrichment and intrusion of hot melts, and accompanied by deformation, hydration, LILE enrichment and LILE/HFSE fractionation. High-P metamorphism of peridotites and eclogites and early migmatization of the country gneisses were virtually coeval and possibly isofacial. The peridotites may represent former mantle-wedge material that was subducted and cooled due to incorporation in a crustal slab and then metasomatized by hydrous fluids left after crystallization of leucosomes. Possible directions for further work on this and other sectors of the Variscan belt where broadly similar rock associations have been found are proposed.