Magma contamination by direct wall rock interaction: constraints from xenoliths from the walls of a carbonate-hosted magma chamber (Vesuvius 1944 eruption)

During the 1944 eruption of Vesuvius different types of xenoliths were ejected. They represent fragments of the walls of a low volume (<0.5 km3) shallow (3–4 km depth) magma chamber. The study of these xenoliths enables us to estimate the amount of contamination occurring at the boundary of a high-T alkaline magma chamber hosted in carbonate rocks. The process of contamination of the magma by carbonates can be modelled, using isotopic and chemical data, as a mixing between magma and marbles. Mass exchanges occur at the boundary between the crystallizing magma and marble wall rocks, where endoskarn forms. The contamination of the solidification front of the chamber is very limited. The solidification front and the skarn shell effectively isolate the interior of the magma chamber from new inputs of contaminants from the carbonate wall rocks. Therefore, the main volume of magma, hosted in the magma chamber, did not undergo any significant mass exchange with the wall rocks.