Dipartimento di Scienze della Terra, Via S. Maria 53, 56126 Pisa, Italy.

This work presents the results of a mineralogical and isotopic (18O, 13C, 87Sr/86Sr) study on xenoliths ejected during the famous 79AD Plinian eruption of Vesuvius. They are considered to be representative of the upper parts of the crystallizing margins of the magma chamber and also of the associated skarn shell. The aim of this study is to describe the thermometamorphic and metasomatic processes which took place at the 79AD magma chamber/wall-rock interface. The results of our research indicate that metasomatism of carbonate wall rocks of the 79AD Vesuvius magma chamber took place due to the infiltration of magmatic fluids, which were exsolved from the peripheral parts of the magma chamber itself. These fluids drive Fe, K, Si, Al and trace elements such as REE, Nb, U, Th, Zr, W, Sb, Pb extracted from the magma into the carbonate host-rocks, thus producing exoskarn. No evidence of later re-equilibrium with low temperature external fluids of meteoric origin was observed. This indicates that only the prograde early stage of skarn formation is recorded in these xenoliths.