La geochimica del granato nelle granatiti della Val Fiorina (Val Grande, Ivrea-Verbano).

In this note we consider the relationship between gabbroic sills and metasediment in a peculiar area of the Ivrea Zone, Val Fiorina, where the dominant rock type is garnetite (modal garnet > 60%). Garnetite layers, which reach a tnickness up to 15 m, invariably separate melasediment and gabbroic silIs. Garnets of these layers are almandine-rich pyralspites. The main variation of the garnet composition which occur trough tne sections is a grossular concentration increase and a decrease of the pyrope-almandine component, away from the metasediments. Garnets are LREE depleted and in general have flat or slightly increasing MREE-HREE patterns. The most striking feature of the REE profiles is the negative Eu anomaly, which decreases away from the metasediment contact. A garnetite petrogenesis related with interaction of basaltic and anatectic melts is here favoured wilh respect to processes of subsolidus element diffusion and a formation of refractory residua after advanced anatexis of metasediments.