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THE SOUTHERN TYRRHENIAN SEA MARGIN 497

eastward migration of the Apenninic arc system and
related back-arc extension induced by the retreat of a
steeply west-dipping subduction zone (RÉHAULT et alii,
1984; MALINVEMO & RYAN, 1986; GUEGUEN et alii, 1997,
1998). In spite of an ongoing debate on the deep geometry
and physical continuity of the subducting slab (i.e. the
slab break-off model: WORTEL & SPAKMAN, 1991; CARMI-
NATI et alii, 1998), recent geophysical and volcanological
data (PECCERILLO, 1985; FINETTI & DEL BEN, 1986; SPAK-
MAN, 1989; AMATO et alii, 1993; SELVAGGI & CHIARABBA,
1995; WILSON & BIANCHINI, 1999) further support the
view of subduction as the dominant geodynamic process.
The southernmost domains of the Apennine-Maghrebide
subduction zone, i.e. the Sicilian and Tunisian segments,
are deformed by the concomitant, slowly north-northwest
moving African plate (MALINVERNO & RYAN, 1986; DE
METS et alii, 1994; GUEGUEN et alii, 1998). This interfer-
ence of the subduction process with the slow northward
drift of Africa is best seen in Sicily, which can therefore
be considered a key-area for the study of the present-day
and recent geodynamics of the central Mediterranean
region (MANTOVANI et alii, 2009; VITI et alii, 2009).
The arcuate shape of the Apennine-Maghrebide sys-
tem is thought to reflect primary compositional differ-
ences in the subducted crustal slabs, with the Ionian
basin, floored by old oceanic crust (DE VOGD et alii,
1992), separating the Sicilian and Apulian continental
forelands. Because of this compositional difference, dur-
ing the last 5 Ma the Calabrian arc continued to roll-back
faster than the adjacent segments, like the Southern
Apennines where the eastward migration of the Apulian
hinge slowed down by a factor of 6 in 10 Ma (GUEGUEN et
alii, 1997, 1998).

TECTONICS OF THE SOUTHERN TYRRHENIAN SEA MARGIN
The tectonic setting of Sicily is characterised by the
superposition of different tectonic units that were origi- Fig. 1 - Structural sketch map of the Central Mediterranean showing
nated at expense of distinct palaeogeographic domains of the major structures and the main tectonic domains.
– Schema semplificato della regione centro-mediterranea, che illustra i
the African mesozoic continental margin (OGNIBEN, 1960). lineamenti tettonici di primo ordine e le principali strutture deformative.
The main recognised units in central-northern Sicily are
the basin-derived Sicilide and Imerese Units, and the plat-
form-derived Panormide Unit. From Oligocene time ing the continental platform of Sardinia (RÉHAULT et alii,
onwards, these units were piled along shallow thrusts and 1987; BOCCALETTI et alii, 1990). Other important N-S
translated southwards during the construction of the trending faults extend for over 150 km and dip west-
Apennine-Maghrebide fold-and-thrust system (CATALANO wards, bounding the Paola Basin (BOCCALETTI et alii,
et alii, 1984). The thrust surfaces have been offset by 1990). The N-S trending faults are not laterally continu-
recent structures related to the opening of the Tyrrhenian ous, but rather appear segmented by E-W trending strike-
Sea during Neogene-Quaternary time (MALINVERNO & slip faults. The northernmost E-W trending faults are
RYAN, 1986). The opening involved significant anticlock- characterised by dominantly left-lateral kinematics (fig. 1;
wise rotations (RÉHAULT et alii, 1987; DEWEY et alii, 1989; SELLI, 1985; LAVECCHIA, 1988). Southward, an important
GUEGUEN et alii, 1997, 1998), and was controlled by faults E-W trending fault zone, known as the Ustica-Eolie Line
of different orientations (fig. 1; BOCCALETTI et alii, 1982, (UEL: BOCCALETTI et alii, 1984) or Southern Tyrrhenian
1984, 1990; WEZEL, 1985). The most important recog- Line (BOCCALETTI et alii, 1990), lies on the southern
nised fault trends are: N-S, E-W and NW-SE (BOCCALETTI Tyrrhenian Sea margin, where it extends for over 400 km.
et alii, 1982). NE-SW trending faults, although present BOCCALETTI & DAINELLI (1982) first inferred for this fault
and locally important in the central Mediterranean a right-lateral kinematic character. Towards the west the
region, are poorly developed along the southern Tyrrhen- UEL can be related to the North Balearic Fracture Zone
ian Sea margin (e.g. see NIGRO et alii, 2000). N-S trending (NBFZ, MAUFFRET, 1976; AUZENDE et alii, 1973) that rep-
faults display a marked extensional character. Slip along resents the southern boundary of the Liguro-Provençal
these faults led to attenuation of the previously thickened Basin and allowed the drift of the Corsica-Sardinia block
continental lithosphere, and to creation of new oceanic during the opening of the basin (AUZENDE et alii, 1973;
floor (KASTENS et alii, 1987). The main recognised struc- RÉHAULT et alii, 1984; GUEGUEN et alii, 1998, among
tures extend for over 300 km and dip eastwards, bound- many others). Right-lateral kinematic character of south-