PETROLOGICAL AND EXPERIMENTAL CONSTRAINTS ON THE PRE-ERUPTIVE CONDITIONS OF LA SOMMATA BASALT AND BROWN TUFFS TEPHRA (AEOLIAN ISLANDS)

This work is focused on two key eruptions of Vulcano Island: 1) the most primitive magma of Vulcano erupted by the La Sommata scoria cone, a silica-undersaturated Ca-rich shoshonitic basalt with olivine-hosted primitive melt inclusions having an ultra-calcic character; 2) the most energetic eruptions of the whole Aeolian Archipelago, the Brown Tuffs (BT) eruptions, which produced several pyroclastic deposits, covering an ample age interval, spread out over a large portion of all Aeolian islands up to the northern coast of Sicily (Lucchi et al., 2008). By complementary studies of melt inclusions and experimental petrology, we pursued the following main objectives: (i) to constrain the pressure temperature-fluid activity during the ascent paths of La Sommata primitive magma and BT basaltic andesite; (ii) to experimentally investigate the influence of H2O in these magma and its effects on the phase relations; (iii) to try to depict a petrological model and to constrain the pre- eruptive conditions of these very different eruptions. In order to obtain the BT pre-eruptive H2O and CO2 contents, preliminarly to the experimental petrology, we performed several analyses on melt inclusions hosted in loose clinopyroxenes sampled from the BT deposits at Vulcano. This step greatly adjuvated the restriction of T, P, H2Omelt conditions for the later experimental petrology approach on BT composition.