Carlo Savelli

Tectonic, volcanic and hydrothermal features of a submarine portion of the Aeolian arc (Tyrrhenian Sea)

Abstract Multibeam, side-scan sonar, remotely operated vehicle and bottom sampling data have been acquired over a sector of the Aeolian arc to assess its volcano-tectonic characteristics and hydrothermal mineralization potential. In this paper we report a description of the areas where major tectonic, volcanic and hydrothermal activity has been observed. There areas are the Basiluzzo area, the Secca dei Pesci area, the southwestern Panarea platform, the Secca del Capo highs, the offshore area between Salina and Lipari, and the eastern slope of Vulcano. The study region lies at the junction of two major E-W and NE-SW trending tectonic lineaments through which the extensional faulting of the Calabrian and Sicilian margins, leading to the formation of the Tyrrhenian back-arc sea, took place. The recent tectonics of the study area, dominated by NE-SW and E-W trending extensional structures, appears to be still controlled by the processes which have originated the Tyrrhenian back-arc opening. Many newly discovered recent volcanic features have been observed e.g.: (1) three pairs of volcanic cones aligned along NE-SW tectonic lineaments in the offshore between Salina and Lipari; (2) a field of fresh, tube and pillow lavas in the eastern offshore of Vulcano; (3) outcrops of fresh volcanic rocks in the Panarea platform, in particular around Basiluzzo islet, suggesting recent volcanic activity. Two types of hydrothermal mineralization were sampled i.e. sediment-hosted sulphide deposits, and Fe-rich crusts and sediments. The polymetallic sulphide deposits were sampled in a depression south of Basiluzzo islet, for which area a kuroko-type hydrothermal system reaching high-temperature black ore deposition is suggested. In the other sectors of the study area, however, a lower-temperature hydrothermal circulation is thought to have originated the Fe-rich tetsusekiei-type samples.

Hydrothermal activity in the SE Tyrrhenian Sea: an overview of 30 years of research

Subduction-related volcanic activity in the Southeast Tyrrhenian back-arc basin has resulted in a large variety of calcalkaline rocks (ranging from arc tholeiitic to shoshonitic and rhyolitic composition), which were emplaced in both oceanic and continental crust. Hydrothermal systems in the SE Tyrrhenian Sea have leached these magmatic rocks, generating a wide range of oxyhydroxide and sulfide deposits. All the hydrothermal occurrences formed at much shallower depths than those from the mid-ocean ridges. Oxyhydroxide deposits (metalliferous sediments, crusts, and nodules) are almost pure hydrothermal formations with insignificant hydrogenetic and diagenetic contributions. They exhibit strong separation of Mn-rich and Fe-rich end members with Mn-rich occurrences dominant. Their geochemistry suggests a relative enrichment of Mn in the hydrothermal systems of the SE Tyrrhenian. The sulfides are Zn- and Pb-rich, but poor in Cu and relatively poor in Fe. This suggests either deep-seated magma chambers or boiling of the hydrothermal fluids beneath the seafloor. As a consequence: (1) Cu and a large proportion of the Fe are deposited as sulfides in the basement rocks and sediment cover; (2) the hydrothermal fluids become relatively enriched in Mn, Zn, and Pb. A number of accessory sulfosalts and selenides not typical of mid-ocean ridge massive sulfides are present.

Shallow-water polymetallic sulfide deposits in the Aeolian island arc

Back-arc basins represent the best-known present-day sites of ongoing massive sulfide deposition in subduction-related tectonic settings. Here we present results obtained from shallow-water sea-floor sampling of barium-rich zinc and lead sulfides genetically analogous to Kuroko-type black ore on an active island arc. The samples come from a newly discovered, hydrothermally active depression on the submerged volcanic edifice of Panarea in the Aeolian island arc (Tyrrhenian Sea). Hydrothermal activity in the area is represented by extensive gas venting associated with white sea-floor aprons of sulfate and iron oxide precipitates. A series of barite-rich sediment samples containing galena, sphalerite, and pyrite was recovered 40 cm below the sea bed at a water depth of 80 m. The deposits represent a unique example of massive-sulfide deposition in an active island arc not yet affected by strong extensional tectonics and reveal that, in this environment, the formation of Kuroko-type black-ore sulfides can take place at shallow water depths.

Anthropogenic Pb in recent hydrothermal sediments from the Tyrrhenian Sea: Implications for seawater Pb control on low-temperature hydrothermal systems

During a 1977 cruise of the R/V Bannock , a core was taken from an area of extensive hydrothermal mineralization located on the slope of Eolo Seamount, Aeolian Arc (Tyrrhenian Sea). The Eolo hydrothermal sediments exhibit unusual Pb isotopic compositions that cannot be solely derived from the plausible natural sources in the area. Mixing considerations indicate that a significant part of the Pb in these sediments is anthropogenic in origin. The anthropogenic Pb was most probably scavenged from the Mediterranean seawater by sinking hydrothermal plume particles. Apparently the hydrothermal products entering the seawater column did not carry significant amounts of Pb extracted from the underlying rocks, so their Pb isotopic compositions were swamped by the seawater Pb. This indicates that Pb in low-temperature hydrothermal products is controlled by the sea-water Pb, not by hydrothermal leaching from underlying rocks.

An updated reconstruction of basaltic crust emplacement in Tyrrhenian sea, Italy

Basaltic crust is present in the oceans and marginal seas. Oceanic accretion from inception to ending may be usefully recognized in small basin setting like the Tyrrhenian. Alternating episodes of strong and moderate extensional tectonics characterized the small Tyrrhenian opening. Hyperextension (drifting) of late-Miocene and latemost Pliocene age was followed by Pliocene and Late Quaternary moderate extension (rifting). Early hyperextension (~7.5–6.3 Ma) acted in the submerged margin of Hercynian Sardinia. Sardinia offshore, E-directed low-angle faults were accompanied by MORB-like volcanism of non linear shape in the shallow Vavilov plain - inherited segment of alpine-age orogen. Late hyperextension (~1.9–1.7 Ma) acted along the central N-S lineament of Vavilov plain, former metamorphic core complex. At the lineament northern side, E-dipping detachment faulting exposed serpentinized peridotite. At the other side, Vavilov volcano was faulted and its east flank tilted westwards. At the same time, volcanism with affinity to transitional MORB induced opening of Marsili basin. The drift episodes were characterized by absence or scarcity of volcanic activity on the conjugated emerged margins. The rift episodes (respectively ~5–1.9 Ma, and ~1/0.8 Ma-Recent) saw growth of major north-south trending volcanoes in bathyal area as intense volcanic activity developed on the continental margins.