I granati delle Fosse di Novale (VICENZA)

Recent soils derived from erosion and alteration of Eocene rocks of the Veneto Volcanic Province (NE Italy) contain detrital millimetric garnets together with many other magmatic and metamorphic minerals, such as zircon, topaz, corundum, beryl, ilmenite and clinopyroxene. EMPA analyses on pink to dark red grains revealed two compositional types, namely almandine-rich (pink) and pyrope-rich (dark red) garnets, respectively. LA-ICP-MS data indicated that the analysed garnets are LREE-depleted, whereas heavy rare earth element (HREE) concentrations are variably enriched, according to the different colour of garnets. This means that, in terms of major elements and trace element patterns, Py-rich garnets are similar in composition to those of typical garnets from mantle-derived rocks (e.g., garnet peridotite/pyroxenite or eclogite). Alm-rich garnets are closer in composition to those of metamorphic rocks (e.g., gneisses and schists). Py-rich garnets could be transported from mantle depths to the surface by Tertiary mantle-derived alkaline basalts of the Veneto Volcanic Province, also carrying zircon megacrysts and spinel peridotite xenoliths. The source of Alm-rich garnets may be found in the crust crossed by the same magmas.