The proximal marine record of the Marsili Seamount in the last 7 ka (Southern Tyrrhenian Sea, Italy): implications for the active processes in the Tyrrhenian Sea back-arc

The volcanism of back-arc basins resembles that of oceanic spreading centers, rifts, and, in vanishing stages, extensional arcs, depending on the amount and rate of the dynamic processes associated to the subduction. Marsili Seamount (MS) represents the axial ridge of the Southern Tyrrhenian Sea back-arc basin, which is connected to the slab roll-backing processes affecting the Calabrian Arc (Italy). The Southern Tyrrhenian Sea back-arc is characterized by a significant decline in the spreading rate with time (2.8-3.1 mm/a to less than 1.8 mm/a in the last 0.78-1 Ma). MS develops between about 1 Ma and 3 ka and mainly consists of lava flows erupted from central and fissural vents. The MS products belong to the calcalkaline association and range in composition from basalts to trachytes. We present new stratigraphic, geochronological, and geochemical data (glass shards and minerals) of tephra from a 2.35 m long gravity core (Marsili1 core) recovered on MS at 943 m b.s.l.. We recognize five tephra [M1 (top of the core) to M5 (bottom)] represented by poorly to high vesiculated ashes. The lowermost tephra M5 emplaced between ca. 7 and 26 ka B.P.; it represents the less evolved distal counterpart of the Unit D related to the Biancavilla-Montalto products of Mount Etna (Sicily). The M1 to M4 tephras emplaced between 2.1 and 7.2 ka B.P. and are related to strombolian-like submarine eruptions of NNE-SSW aligned MS vents. The composition of the M1-M4 glasses ranges from basaltic trachyandesites to andesites and trachytes. The M1 to M4 magmas mainly originated by crystal fractionation from a heterogeneous mantle source with varying LILE enrichments by subductionrelated fluids. The degree of evolution of the MS magmas increases with decreasing time. The formation of vertically stacked magma storage zones at the crust/mantle interface and within MS is related to the vanishing Southern Tyrrhenian Sea opening, which implies the rapid (< 1 Ma) evolution from a slow spreading back-arc setting to an arc system.