The Establishment of the Steady-State Activity at Stromboli Volcano (Italy): Evidence from Diffusion and Mixing Processes Revealed at Mineral Scale

The present-day activity of Stromboli is characterized by strombolian explosions ejecting black scoriaceous lapilli and ash. This persistent activity is interrupted by effusive eruptions and more energetic explosions (paroxisms) emitting black scoriaceous bombs, lapilli, and gold pumices. The entire system is in a persistent steady-state activity whose driving forces are still not completely understood. Investigating the evolution of the plumbying system toward the present-day condition is thus crucial to better constrain and understand the onset and development of the present-day activity. We studied in detail two selected samples representative of the transitional eruptive phase from the pre-Sciara period to the present-day: (i) an older spatter lava sample from the pyroclasic succession of Chiappe Lisce (Post-Pizzo activity) emplaced prior the beginning of the present-day activity; (ii) a black scoria spatter covering the youngest collapse scarp, probably ejected during one of the early paroxisms of the present-day activity. Both samples have similar paragenesis with phenocrysts of olivine, clinopyroxene, plagioclase and oxide. We recognize several different types of clinopyroxene textures with different recurrence among the two samples. In detail, multiple banded clinopyroxene with evident resorbing features, characterizes the older Chiappe Lisce shoshonite sample, recording several pulsatory intrusions of new mafic magmas into the system and pointing to the establishment of the steady-state condition. Contrarily, single diffused band and/or patchy cores are found in the present-day basaltic paroxism scoria. We applied the diffusion chronometry to suitable clinopyroxene crystal bands to temporally constrain the occurrences of these refilling events. Decadal timescales characterise the shallow magma reservoir from the post-Pizzo period onward pointing to a progressive transition toward the present-day contidion.