Melilitolite intrusion and pelite digestion by high temperature kamafugitic magma at Colle Fabbri, Spoleto, Italy

A subvolcanic body in Colle Fabbri (Umbria, Central Italy) intrudes sedimentary rocks and the overlaying extrusive breccia. The intrusive rock is melilitolite with essential leucite, kalsilite, and wollastonite plus accessory Ti-garnet, Ti–Al–Fe3+-clinopyroxene, magnetite, perovskite, rankinite, Si-bearing apatite, Fe–Ni sulphides, and carbonate/zeolite. Bulk chemistry of melilitolite indicates a strong SiO2-undersaturation, extremely high CaO composition, and strong initial potassic character. Sr and Nd isotopic ratios support a link with the source of kamafugites and carbonatites found in the same region. The igneous contact rock contains variable amounts of quenched clinopyroxene, anorthite, sanidine ± wollastonite, plus spinel and glass. Extremely high temperature melilitolite magma digested pelite country-rock, thus leading to a unique mineral composition. The homogenisation temperatures of mineral inclusions in contact rock demonstrate that crystallisation occurred well above 1230 °C. A large thermal aureole formed in a local clinker-like breccia, characterised by the association of felsic glass + indialite + tridymite ± Ti-magnetite, confirms high-temperature emplacement. Metasomatic/thermometamorphic phenomena favoured zone-specific mineralisation of hydrated Ca-silicates, hydrated complex sulphates and zeolites in breccias and encasing rocks.