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G. Lavecchia et al. / Tectonophysics 445 (2007) 145–167 151

order kinematic units identified in Fig. 4 (KU 1, 2, 3 and
4); the sub-units (KU 1a, 1b and 2a, 2b, 2c in Fig. 4) are
delimited by the hangingwall splays from the basal
thrusts of the various slices.
In our interpretation, since late Oligocene–early
Miocene times, the slices were sequentially overthrust
southward one over the next, moving above NNW to
NNE-dipping basal detachments; out of sequence
thrusts developed at shallower levels. The crustal
thinning and normal faulting in northern Sicily and in
the Tyrrhenian Sea often occurred through tectonic
inversion in late Miocene–Pleistocene times (Nigro and
Renda, 1999; Pepe et al., 2000; Giunta et al., 2000;
Guarnieri et al., 2002) of pre-existing major thrust
planes. The Caccamo–Caltavuturo–Troina alignment,
which in the map of Fig. 2 marks the front of the Plio-
Quaternary upper crust extension in northern Sicily, is
interpreted by us as a normal and normal–oblique
deformation zone which reactivates and inverts the
WNW–ESE striking right-lateral Caccamo shear zone
(Del Ben and Guarnieri, 2000; Guarnieri, 2004) and the
eastern portion of the Kumeta–Alkantara right-lateral
strike–slip lineament (Ghisetti and Vezzani, 1984;
Renda et al., 2000).

3. The Sicilian Basal Thrust

The Sicilian Basal Thrust (SBT), i.e. the sole thrust of
the outermost kinematic unit (KU 1a in Fig. 4) of the
Sicilian fold-and-thrust system, extends with southward
convex arched shape offshore of Sciacca–Agrigento–
Licata and onshore from Gela to Niscemi, Mineo,
Scordia and the southern Catania plain. In section view
(Fig. 5) it deepens northward, across the entire crust,
intersecting the Moho at a depth of about 30 km beneath
the northern coast of Sicily. An important hangingwall
splay outcrops some kilometres inward and extends with
the same arched shape along the alignment Sciacca–
Agrigento–Settefarine–Caltagirone–Ramacca–Catania
Fig. 5. Interpretative crustal sections across the study area. The traces
of sections are given in the map in Fig. 4. The various tectonic (Figs. 2 and 4). Starting from the SBT geometry depicted
elements schematically depicted in the profiles (thrusts and normal in the five crustal sections of Fig. 5, the 0-to-30 km SBT
faults) correspond to those in structural map of Fig. 2 and represent the depth-contour lines (e.g. isobaths) have been here
down-dip prosecution of the boundary between the kinematic units of reconstructed and drawn in Fig. 6. The isobaths
Fig. 4; the numbers within the crustal slices are referred to the first- substantially follows the surface SBT trajectory; they
order kinematic units identified in Fig. 4. The various Moho segments
at the base of the crust are mainly deduced from Finetti (2005) with are more closely spaced near the western and eastern
some information from Chironi et al. (2000). Key: c.l. = coast line, concavity and more distant in the central sector. This
SBT = Sicilian Basal Thrust. feature reflects the SBT dip-attitude, which is steeper in
proximity to the Mazara–Sciacca and Gela–Catania
areas and flatter in the Agrigento–Canicattì–Licata area.
entire crust, linking the sedimentary cover and the A cessation of the compressional activity of the
deep crust structures. In Fig. 5, we schematized four Sicilian Thrust belt in Quaternary times is commonly
northward-dipping slices, which correspond to the first accepted in the literature, mainly based on the