Constraining magmatic fluxes through thermal modelling of contact metamorphism

The thermal evolution of a contact aureole is strongly dependent on the emplacement mode of the intrusion that is causing the thermal anomaly. Inferences on the emplacement mode can be made if solid temperature estimates are available. The contact aureole of the Western Adamello Tonalite provides a unique combination of magma ascent close to the host rock and suitable rock chemistry. We use three mineral reactions at different distances in the aureole in combination with phase petrology to estimate temperatures. These temperatures are not reproducible by thermal models considering the emplacement of the intrusion as a single batch. The external zone of the intrusion represents a feeder conduit in which magma was transported. We investigated the thermal effect of the conduit on the host rocks using thermal models. Different thermal profiles for the aureole are obtained by varying flow/no-flow times, conduit thickness and magma temperature. We show that only a few combinations match the temperature constraints in the aureole, and that the amount of magma transported through the conduit can be calculated. A comparison with time-averaged fluxes of recent volcanoes and the presence of reworked volcanic sediments in the surroundings of the Adamello batholith indicate that the calculated rates and volumes are plausible.