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THE SOUTHERN TYRRHENIAN SEA MARGIN 499

E-W trending anomaly on the magnetic anomalies map
(AGIP, 1981; GALDEANO & ROSSIGNOL, 1977). This anom-
aly terminates eastward against another NW-SE trending
anomaly that runs from the Eolie Islands to the Taormina
Line in Sicily. Whereas westwards, it can be related to the
strong anomalies that outline the North Balearic Fracture
Zone (NBFZ: MAUFFRET, 1976; AUZENDE et alii, 1978), a
lithospheric-scale structure that represents the southern
boundary of the Liguro-Provençal Basin. These strong mag-
netic anomalies trend N130° (GALDEANO & ROSSIGNOL,
1977) and limit to the east the small triangular fan-shape
anomalies domain that lies southwest of Sardinia. On seis-
mic lines offshore the Balearic Islands, the NBFZ is clearly
identified by a remarkable offset in the basement (fig. 3) Fig. 3 - Seismic profile across the North Balearic Fracture Zone
and magmatic bodies (MAILLARD & MAUFRET, 1999). (NBFZ, after MAILLARD et alii, 1999). This section illustrates nicely
Above this structure the Messinian salt layer is disturbed the offset of the top of the basement across the NBFZ. Note the pre-
(GAULLIER, 1993; GUEGUEN, 1995) showing huge elongated sence of the magmatic intrusion that produces the strong magnetic
anomalies observed along the entire trace of the NBFZ through the
salt domes parallel to the fracture zone. The NBFZ has its Liguro-Provençal basin.
onshore continuation in the Catalan volcanic province of – Profilo sismico attraverso la Zona di Frattura Nord-Balearica (NBFZ,
Spain, which is characterised by middle Miocene to Pre- da MAILLARD et alii, 1999). Questa sezione illustra efficacemente la
sent-day alkaline magmatism linked to extensional tecton- componente verticale del rigetto registrato dal top del basamento attraverso
le strutture della Zona di Frattura Nord-Balearica. Si noti la presenza
ics (MARTÌ et alii, 1992). The southern Tyrrhenian Sea mar- dell’intrusione magmatica che determina le intense anomalie magnetiche
gin is still very active as shown by the distribution of osservabili lungo tutta la traccia della Zona di Frattura Nord-Balearica
crustal earthquakes along the coast of Northern Sicily attraverso il Bacino Ligure-Provenzale.
(FREPOLI & AMATO, 2000). These authors analysed sparse
background seismicity data in Italy to investigate the state
of stress of deformed continental crust and to determine
the mean orientations of the principal stress axes. In partic-
ular, they analysed data from the western-central sector of
northern Sicily, and from the Eolian Islands. Based on a
compilation of 47 seismic events (22 events for the western-
central sector of northern Sicily, plus 25 events for the
Eolian Islands sector), these authors inferred a mean
N99°E direction for the axis of maximum horizontal com-
pression (s1 max) for western Sicily, and a mean N162°E
direction for the axis of maximum horizontal compression Fig. 4 - Structural data from the Marettimo (a), Trapani (b), San Vito
(s1 max) in the Eolian Islands sector. In spite of local varia- (c) faults, and from the Gratteri - Mt. Mufara Line (d). Equal area
projection, lower hemisphere. All faults mean trend NW-SE dip
tions, the orientations of the maximum compression axes mainly toward NE and subordinately toward SW, and are mainly
are well clustered around a mean 17° plunge towards dextral strike-slip in character, with local transtensional and tran-
N99°E, and 13° plunge towards N342°E, respectively. As for spressional components.
the directions of the minimum compression axes (s3 min), – Dati strutturali e cinematici (proiezione equiareale, emisfero inferiore)
raccolti lungo le Faglie di Marettimo (a), di Trapani (b), di San Vito (c)
they appear to fall within a great circle, indicating a greater e lungo il Lineamento Gratteri-M. Mufara (d). Tutte le faglie hanno
variability than that of the maximum compression axes. direzione media NW-SE, immergono prevalentemente verso i quadranti
The mean calculated minimum compression axes plunge nord-orientali e solo subordinatamente verso i quadranti sud-occidentali,
55° towards N215°E, and 37° towards N82°E, for western e sono caratterizzate da una cinematica di tipo trascorrente destro, con
occasionali componenti di deformazione transtensiva e transpressiva.
Sicily and the Eolian Islands, respectively.

STRUCTURAL DATA
who first recognised dextral strike-slip deformations (see
The NW-SE trending faults of the southern Tyrrhenian also LENTINI et alii, 2006). One main difference with previ-
Sea margin, i.e. the Marettimo, Trapani, San Vito and ous contributions is that the latter also considered faults that
Palermo faults, are magnificently exposed in northern Sicily were active during the uppermost Pliocene time.
and in the Egadi Islands, thus providing an excellent oppor- By contrast with the exhaustive datasets from the
tunity to define their kinematics by means of structural Marettimo, Trapani and San Vito faults, to date compara-
investigations (LENTINI et alii, 2006). In order to unravel the tively little information is available on the kinematics of
recent evolution of northern Sicily, we studied selected stru - the Palermo fault. Therefore, our structural analysis was
ctures along, or in the immediate vicinities of these major mainly focused on the orientation and kinematics of this
faults, and restricted our analysis to faults that offset Plei - fault and associated minor fabrics. The scale of recog-
stocene or younger deposits. Measurements of orientation nised structures related to the Palermo fault ranges from
data such as mechanical striations and shear fibres along the macroscopic to mesoscopic. In general, minor structures
Marettimo, Trapani and San Vito faults indicate a mean dex- are particularly abundant in the immediate vicinities of
tral strike-slip character, with both minor transtensional and the major fault surface, where important cataclastic belts
transpressional components (fig. 4). These data are in broad are developed. The main recognised minor structures
agreement with the results of previous analyses by NIGRO et consist of shear and extension fractures, pinnate joints
alii (2000), RENDA et alii (1999, 2000) and GUARNIERI (2004), and calcite veins, that are frequently developed within the