Insight on the recent magmatic system of Lipari and Vulcano on the basis of new structural and geochemical data

Recent studies, based on field and geochronological data on the available chronicles, show that in the southern sector of the Aeolian Archipelago the historical volcanic activity occurred close in time or, in some case, simultaneously at different vents along a NS tectonic alignment: in the early XIII c. at Lipari (Mt Pilato-Rocche Rosse eruption), La Fossa of Vulcano (Commenda and Palizzi eruptions) and Vulcanello, and in the XVII-XVIII c. at La Fossa (Pietre Cotte) and Forgia and, possibly, at Vulcanello. Petrochemical investigations on the erupted magmas suggest the existence of a polybaric feeding system connected to deeper shoshonitic-latitic magmas that periodically refills the shallow system. The reactivation of the shallow systems directly originates latitic-trachytic eruptions and/or is the trigger for the rhyolitic ones. Structural data allowed to get information about the kinematic of the structures and the local and regional stress field, as well as to better understand the structural relationships among the two islands and stress regime -recent magmatism. Most of the structures have a N-S and NNW-SSE direction and in both islands a distensive regime is dominant. As a whole, structures are oriented N-S at Vulcano, and they curve at NNW-SSE in the North and South of Lipari. When they are present, kinematic indicators support a mainly normal component (pitches between 80 and 130°, indicator of dip-slip), with a subordinate strike-slip component. Structural results suggest a possible change of the stress field that could vary at a regional scale, from a pure strike-slip regime along the Tindari-Letojanni fault, to an extensional regime at Vulcano and Lipari. Most of recent products are only marginally faulted or not faulted at all. Recognized structures may have a magmatic origin and not necessarily be related to regional systems with estimable recurrence times. At Vulcano a key area for the understanding of tectonic deformation and its relationship with magma uplift is the M. Saraceno area where (a) the stratigraphic sequence and the volcanic structures indicate the locus of a probable recent activity, successive or coeval to the formation of Fossa caldera, and (b) faults and fracture are N-S oriented, as the structures that guided the magmatic upraise of historic activity. A C14 age on coal fragments found in the upper portion of Saraceno scoriae give an age of 8890 +/- 30 BP which well fit with the previous age determination. We also performed textural and chemical (major and trace elements) analyses on mineral phases including Sr-isotope ratios on core-rim traverses and groundmass by micro-drilling technique. At this aim, we selected the most primitive products (latitic enclaves and their hosts) from the most recent eruptions of La Fossa and the 1739-1888 and other historical eruptions of Lipari and Vulcano. Particular attention has been devoted to latites erupted during the last activity (1888-90) and latites erupted during the post-medieval activity (Gran Cratere). They represent the most recent ascent of a relatively poorly evolved magma at La Fossa, an event that could have triggered the last eruptive phases. Results provide informations on the path of rising magmas, storage time and depth of magma chambers, pre- and syn-eruptive mechanisms and their relative timescales. The comparison of chemical composition of the historical latites in terms of trace elements of whole rock and single minerals confirms their strong similarity. Micro-Sr isotope data analyzed on plagioclase, sanidine and clinopyroxene show a large variability (0.70460- 0.70590), also among the minerals of a same sample. Clinopyroxene cores, however, have lower Sr isotope ratios than sialic phases and show quite similar values in all the studied samples, suggesting their origin from a common magma. This characteristic seems to confirm that the same latitic magma may refill the shallower part of the feeding system. Furthermore, the higher Sr-isotope ratios of the sialic phases may suggest their crystallization at lower depth during the crustal contamination processes.