First documented deep submarine explosive eruptions at the Marsili Seamount (Tyrrhenian Sea, Italy): A case of historical volcanism in the Mediterranean Sea

• Submarine explosive eruptions at the Marsili Seamount in the last 3–5 ka
• Marsili is still active, it should be monitored and the hazard evaluated.
• Coexisting arc and back-arc volcanism in the Tyrrhenian Sea during Holocene

The Marsili Seamount (MS) is an about 3200 m high volcanic complex measuring 70 × 30 km with the top at ~ 500 m b.s.l. MS is interpreted as the ridge of the 2 Ma old Marsili back-arc basin belonging to the Calabrian Arc–Ionian Sea subduction system (Southern Tyrrhenian Sea, Italy). Previous studies indicate that the MS activity developed between 1 and 0.1 Ma through effusions of lava flows. Here, new stratigraphic, textural, geochemical, and 14C geochronological data from a 95 cm long gravity core (COR02) recovered at 839 m bsl in the MS central sector are presented. COR02 contains mud and two tephras consisting of 98 to 100 area% of volcanic ash. The thickness of the upper tephra (TEPH01) is 15 cm, and that of the lower tephra (TEPH02) is 60 cm. The tephras have poor to moderate sorting, loose to partly welded levels, and erosive contacts, which imply a short distance source of the pyroclastics. 14C dating on fossils above and below TEPH01 gives an age of 3 ka BP. Calculations of the sedimentation rates from the mud sediments above and between the tephras suggest that a formation of TEPH02 at 5 ka BP MS ashes has a high-K calcalkaline affinity with 53 wt.% < SiO2 < 68 wt.%, and their composition overlaps that of the MS lava flows. The trace element pattern is consistent with fractional crystallization from a common, OIB-like basalt. The source area of ashes is the central sector of MS and not a subaerial volcano of the Campanian and/or Aeolian Quaternary volcanic districts. Submarine, explosive eruptions occurred at MS in historical times: this is the first evidence of explosive volcanic activity at a significant (500–800 m bsl) water depth in the Mediterranean Sea. MS is still active, the monitoring and an evaluation of the different types of hazards are highly recommended.

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