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GEODYNAMICS OF THE SOUTHERN TYRRHENIAN 79

dip eastwards, bounding the continental platform of Sar- les, from macroscopic to mesoscopic. The main struc-
dinia (fig. 1; BOCCALETTI et alii, 1990a, b). Other impor- tures extend for over 100 km, and are generally associated
tant N-S trending faults extend for over 150 km and dip to complex networks of minor faults ranging in size from
westwards, bounding the Paola Basin (fig. 1; BOCCALETTI a few centimetres to several kilometres. The kinematics of
et alii, 1990a, b). The N-S trending faults are not laterally NW-SE trending faults has been recently defined through
continuous, but rather appear segmented by E-W trend- structural measurements by NIGRO et alii (2000) and
ing, dominantly strike-slip faults. The northernmost E-W RENDA et alii (2000) from the Marettimo, Trapani and
trending faults are characterised by dominantly left-late- San Vito faults (See fig. 1 for location). In this section we
ral kinematics (fig. 1; SELLI, 1985; LAVECCHIA, 1988). briefly review the main results of the aforementioned
Toward the South, an important E-W trending fault lies studies, referring the reader to them for additional
on the southern Tyrrhenian Sea margin, and extends for details. Mechanical striae and slickensides on the fault
over 400 km, from Ustica to the Eolian Islands (Ustica- surfaces consistently indicate right-lateral strike-slip kin-
Eolie Line: BOCCALETTI et alii, 1984; Southern Tyrrhenian ematics, though with a local, minor extensional slip com-
Line: BOCCALETTI et alii, 1990a, b). BOCCALETTI & DAI- ponent. The resulting kinematics is therefore best defined
NELLI (1982) first inferred for this fault a dominantly as transtensional The investigated faults are systemati-
right-lateral kinematic character. This interpretation has cally associated to development of a well-defined cata-
been questioned by more recent contributions, mainly clastic foliation, indicating that faulting and fracturing of
based on seismic interpretation and deep sea drilling data the host sediments occurred at very shallow crustal levels,
(e.g. see KASTENS et alii, 1988; KASTENS & MASCLE, 1990; under non-metamorphic conditions. The mean trend of
SARTORI, 1989, 1990; PEPE et alii, 1998, 2000, among the cataclastic foliation is N-S, in agreement with the
many others), according to which the E-W trending struc- bulk dextral kinematics inferred from fault striae analy-
tures are normal faults, and the southern Tyrrhenian tec- sis.
tonic boundary represents a passive, i.e. purely exten- The Gratteri-Mt. Mufara Line (See fig. 1 for location)
sional, margin. The interpretation of the southern had a more complex history. It formed during Late Trias-
Tyrrhenian margin as a strike-slip, or as an extensional sic time as a normal fault, separating differently subsid-
deformation zone, is still matter of debate, and the data ing blocks, and was subsequently reactivated as a trans-
presented below are also aimed to provide new indepen- fer fault and as a lateral thrust ramp during the
dent evidence to help unravel the kinematic character of Oligocene-Miocene and Miocene-Pliocene time intervals,
this boundary. Another major E-W trending structure, the respectively (RENDA et alii, 1999). This reactivation pro-
Mt. Kumeta-Alcantara fault onshore northern Sicily, cess may provide an explanation to account for the pre-
extends for over 300 km, from the Trapani Mts. to Mt. sent, anomalous NNW-SSE orientation of the Gratteri-
Etna (fig. 1; RUGGIERI, 1966; GHISETTI & VEZZANI, 1984, Mt. Mufara Line, that is different from the mean NW-SE
and references therein). Detailed structural analyses orientation of adjacent faults. The distribution of seismic-
revealed for the Mt. Kumeta-Alcantara fault a general ity in the Madonie Mountains (see fig. 2; FREPOLI &
right-lateral kinematic character (GHISETTI & VEZZANI, AMATO, 2000), suggests that this structure was further
1981, 1984). recently reactivated as a dextral strike-slip fault (e.g. see
In addition to N-S trending extensional faults and E- RENDA et alii, 2000).
W trending strike-slip faults, other structures are recog- All structural data collected along the Marettimo, Tra-
nised in the southern Tyrrhenian Sea margin. Most struc- pani and San Vito faults, and along the Gratteri-Mt.
tures trend NW-SE (BOCCALETTI et alii, 1982). FINETTI & Mufara Line, are consistent with a sub-horizontal, NW-
DEL BEN (1986) named the most important NW-SE SE directed shortening.
trending structures as follows, from west to east: the
Marettimo fault, the Trapani fault, the San Vito fault, the
Palermo fault and the Etna fault (fig. 1). RENDA et alii GEOPHYSICAL DATA
(1999) further recognised a major NNW-SSE trending
structure, the Gratteri-Mt. Mufara Line, that character- In this section we briefly review the available geo-
ised the tectonic evolution of the Madonie Mountains, physical information that allows for definition of the
and that experienced repeated reactivation through time. main crustal – and lithospheric-scale features of the
All these structures occur within a 400-km long, 150-km Southern Tyrrhenian Sea margin (MORELLI et alii, 1975;
wide deformation belt, bounded by the E-W trending CALCAGNILE & PANZA, 1981; PANZA, 1984; SCARASCIA et
Ustica-Eolie and Mt. Kumeta-Alcantara faults (fig. 1). The alii, 1994; AGIP, 1981; GALDEANO & ROSSIGNOL, 1977;
exposed portions of NW-SE trending faults in the Egadi FREPOLI & AMATO, 2000). The Southern Tyrrhenian Sea
Islands and in northern Sicily exhibit a marked strike-slip margin matches the transition from a normal continen-
component (ABATE et alii, 1988, 1998; MAUZ & RENDA, tal crust, ca. 40 km thick underlying northern Sicily, to
1995; RENDA et alii, 1999, 2000). a strongly thinned continental crust, ca. 10-15 km thick
The activation of N-S, E-W and NW-SE trending fault underlying the southern Tyrrhenian Sea (fig. 2): as
systems is generally referred to the Early Pliocene-Recent already mentioned, some parts of the southern Tyrrhen-
interval (BOCCALETTI & DAINELLI, 1982; GHISETTI & VEZ- ian Sea are also locally floored by newly created oceanic
ZANI, 1982, 1984; FINETTI & DEL BEN, 1986). crust (fig. 1; KASTENS et alii, 1987). The modes of normal
to thinned continental crust transition are controversial.
According to MORELLI et alii, 1975 the transition occurs
STRUCTURAL DATA gradually, with a base of the continental crust that slo-
pes gently from the Tyrrhenian Sea south-westwards
The NW-SE trending faults of the southern Tyrrhen- under Sicily. According to SCARASCIA et alii (1994),
ian Sea margin are recognised on a wide variety of sca- instead, this transition is abrupt, with a significant step