What controls sheet intrusion in volcanoes? Structure and petrology of the Stromboli sheet complex, Italy

A multidisciplinary study has been conducted on 109 intrusive sheets of Stromboli. The relation between sheet injection conditions with the magmatic and structural variations of the volcano, and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined.During its subaerial activity (the last 100 ka) Stromboli experienced periods of extrusive growth and sheet intrusions, alternated to caldera and lateral collapses of the NW Sciara del Fuoco flank. The sheet intrusions, similar to the extrusive rocks, span a large compositional range from calc-alkaline to potassic, through high-K calc-alkaline and shoshonitic series. The most evolved compositions of the effusive rocks, however, have not been found as intrusions, whereas some mafic and basic magmas of sheets were never erupted.The repeated time change of location of the intrusions from Strombolicchio to the NE–SW trend passing trough the inferred Paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast, and the subsequent onset of a clear NE–SW-elongated magma chamber located along the main Stromboli weakness zone. The Stromboli evolution in the last 100 ka has been characterized by the persistent N 10–55° E intrusion direction, which reflects the influence of the edifice's state of stress on the magma feeding paths. After 13 ka ago, sheets mainly intruded along to the sector collapse scarps in a circum-amphitheatre geometry, which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters.