Magma mixing during the 2001 event at Mount Etna (Italy): Effects on the eruptive dynamics

摘要

During the 2001 eruptive episode three different magmas were erupted on the southern flank of Mount Etna volcano from distinct vent systems. Major and minor element chemistry of rocks and minerals shows that mixing occurred, and that the mixed magma was erupted during the last eruptive phases. The space-time integrated analysis of the eruption, supported by geophysical data, together with major and trace element bulk chemistry (XRF, ICP-MS) and major and trace mineral chemistry (EPWA, LAM ICP-MS), support the following model: 1) trachybasaltic magma rises through a NNW-SSE trending structure, connected to the main open conduit system; 2) ascent of an amphibole-bearing trachybasaltic magma from a 6 km deep eccentric reservoir through newly open N-S trending fractures; 3) just a few days following the eruption onset the two tectonic systems intersect at the Laghetto area; 4) at the Laghetto vent a mixed magma is erupted. Mixing occurred between the amphibole-bearing trachybasaltic magma and an inferred deep more basic end-member. The most relevant aspect in the eruptive dynamics is that the eruption of the mixed magma at the Laghetto vent was highly explosive due to volatile content in the magma. The gas phase formed, mainly because of the decreased volatile solubility due to rapid fractures opening and increased T, related to mixing, and partially because of the amphibole breakdown.