Evolution of the eruptive activity at Stromboli (Aeolian Islands - Italy) during the last 4 millennia. A tephrostratigraphic investigation on the early-phase of Recent Stromboli Eruptive Epoch

Stromboli is famous for its persistent explosive activity that has been studied from various perspectives over the last century. By contrast, there is controversial information about the volcanic history regarding the period between 6000 years ago and the onset of the present-day activity. Here, we present a comprehensive tephrostratigraphic investigation of the pyroclastic sequences that predate the onset of the present-day activity. This study integrates field observations, sedimentological analyses and radiometric 14 C dating, together with detailed textural, petrographic and geochemical characterisation of juvenile clasts. Specifically, we document two superimposed volcanoclastic sequences, Members A and B, consisting of sub-conformable pyroclastic beds of lapilli and ash, interspersed with massive epiclastic deposits. While these sequences exhibit similar lithological features, indicating comparable eruptive dynamics, they are distinguishable for their glass composition and for a distinct chronostratigraphic framework. In particular, a major change in the glass composition of the magma occurred between 3200 and 1780 years ago, shifting from high-K calc-alkaline (HKCA) to shoshonitic (SHO) affinity, composition that still persists in the present-day. We recognise four distinct eruptive periods with HKCA composition within Member A and two eruptive periods with SHO composition within Member B, both predating the onset of the present-day activity. Also, within Member A, we observed the earliest coexistence and mingling of two end-members with different texture and composition. This suggests that the feeding system of Stromboli could have been very similar to the present-day since at least 3200 years ago. It likely comprises two distinct magma bodies at different depths containing magmas with different compositions and porphyritic characteristics that occasionally interact prior to eruptions. Our findings contribute to a comprehensive reconstruction of Stromboli's volcanic history and hold practical significance for anticipating and mitigating potential future volcanic events. • Recent Stromboli activity began c. 3200 years BP, much closer than previously believed to the end of Neostromboli. • The eruptive history developed across six eruptive periods, characterised by peculiar glass composition. • The chronological, volcanological and geochemical overlap between Lower Sequence and Pizzo Sopra la Fossa confirms that these are produced by the same activity during the Eruptive sub-Epoch 6a. • We documented an abrupt shift from HKCA magmas, which erupted between 3200 and 1780 yrs. BP, to SHO magmas erupted thereafter, with no coexistence, nor intercalations between them. • The onset of the present-day activity is gradual, and based on the shift in magma composition likely occurred 830–684 yrs. BP, although the present-day eruptive style already began from 1080 to 1278 yrs. cal. BP.