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2 F. NIGRO
coastal areas, it is possible to observe a widespread presence
of hanging-wall tilting low angle norma! faults (listric
faults), cutting the strike-slip fault systems. In Centrai Sici-
ly, the prevalently E-W trending transcurrent faults are
often buried, and recognisable due to the presence of many
large scale en-echelon fold systems that involved the Plio-
Pleistocene successions.
The exposed neotectonic structures represent the shal-
low evidences of deep geologica! mechanisms that contro!-
!ed the recent evolution ofthe Peri-Tyrrhenian Belt. The re-
lated deep structures produced also different geophysical
anomalies; the generai trend ofthese parameters can help to
understand the regional architecture ofthe analysed area.
Some tectonic phases recorded in the Plio-Pleistocene
sequences have been recognised, pointing out the repeated
change in time of their character (compressional/transpres-
sional and extensional). The biostratigraphic data of the
most recent sequences involved in the deformation have
dated, in some places, the main neotectonic phases.
The comparison of the trend and significance of out-
cropping structures, carried out through the structural analy-
sis and large-scale field observations, with those charac-
terising the surrounding submerged areas of Sicily (recog-
nised from the interpretation of already published high reso-
lution seismic profiles already described), make it possible
to fit ali data in a structural mode! ofthe Tyrrhenian opening
during the last 5-6 Ma.
The change in time of stress field, recorded in the
polyphase deformed Plio-Pleistocene sequences, permits to
hypothesise on rhythmical tectonics in Centrai Mediterra-
nean related to a group of vectors in space that express sev-
era! forces characterising the recent geodynamic evolution
ofthe analysed area.
A possible mode! of the Tyrrhenian basin evolution
given in this paper considers the widespread presence of
strike-slip structures that might have controlled the basin
formation and evolution, and the re-deformation ofthe pre-
existing peri-Tyrrhenian Belt in the analysed area during the
last few Ma.
TYRRHENIAN BASIN
GENERALBACKGROUND
Two groups of models have been proposed for the Tyr-
rhenian Sea opening:
- vertical motion models, explained as the consequence
of subcrustal erosion mantle mechanisms and intrusion of
oceanic-type magmatism (Morelli, 1970; Selli, 1981, 1985;
Heezen et al., 1971; Selli & Fabbri, 1971 ), or large scale
mantie diapiric upwelling ("krikogenic" mode! of Wezel,
1981, 1985);
- horizontal motion models based on the plate tectonics
framework and on the occurrence of crustal strike-slip fault
systems (back-arc type basin, Boccaletti & Guazzone, 1972;
Dewey et al., 1973, 1989; Alvarez et al., 1974; Boccaletti et
al., 1976; Biju-Duval et al., 1977; Boccaletti et al., 1984;
Rehault et al., 1984a, b, 1987a; Kastens et al., 1988).
GEOPHYSICAL DATA
Geophysical data from severa! projects (ODP, DSDP,
CNR, ESCARMED) carried out in the last twenty years
make it possible to define the deep architecture of the Tyr-
rhenian area. Fig. l shows a synthesis ofthe main results of
published geophysical research in the Centrai Mediterra-
nean (Morelli, 1970; Colombi et al., 1973; Finetti & Mo-
relli, 1973a,b; Morelli et al., 1975; Lort, 1977; Schutte,
1978; Fabbri & Curzi, 1979; Panza et al., 1980; AGIP, 1981;
Finetti, 1982; Steinmetz et al., 1983; Della Vedova et al.,
1984; Req et al., 1984; Finetti & Del Ben, 1986; Rehault et
al., 1987b).
The reconstructed physiography of the basin is charac-
terised by a NW-SE trending bathial plain, more than 3,000
m deep, made up a discontinuous oceanic type crust and
covered by Tortonian to Lower Pleistocene depositional se-
quences. Severa! NNE-SSW trending small basins, mostly
filled by sedimentary sequences cut by volcanic dikes dis-
sect the bathial plain. In major basins (Magnaghi, Vavilov
and Marsili) many submerged volcanoes are located,
aligned along a NW-SE trend, from the Sardinia scarp to the
Aeolian Volcanic Are. Towards the NW, the bathial plain is
bordered by a very important structural lineament (Centrai
Fault) that divides to the west the Comaglia Terrace and the
Sardinia Basin. Southwards and southeastwards, the bathial
plain passes into a number of small basins (Erice, S. Vito,
Cefalù, Orlando, Gioia; Paola; Fabbri et al., 1981; Wezel et
al., 1981), superimposed on the strongly deformed carbon-
ate and siliciclastic sequences of the Sicily-Apennine
Thrust Belt, and filled by the Plio-Pleistocene clastic se-
quences. The age of the lowermost depositional sequences
filling these basins youngs towards the E and SE.
The deep basinal area gradually passes to the Sicilian
Shelf, where the previously described small basins are rec-
ognised. These are mostly the result of half-graben forma-
tion and, in places, of inversion structures involving Pleisto-
cene deposits (Fabbri et al., 1981; Wezel et al., 1981 ). Some
emergent volcanic cones (Ustica and Aeolian Islands) are
also present in this area.
The measured heat flow (Della Vedova & Pellis, 1979;
Della Vedova et al., 1984, 1991) indicates different prov-
inces and three maxima corresponding to the Mag-
naghi-Vavilov-Marsili area (more than 200 mW/m2), while
a minimum characterises the Poseidone-Marsili and the De
Marchi-Magnaghi-Vavilov Seamounts (less than 50
mW/m2). The heat flow gradually decreases from the cen-
trai part ofthe Tyrrhenian basin towards the peripheral areas
(less than 100 mW/m2 towards Tuscany, 100 mW/m2 in the
Sicily-Calabria-Campania coastal areas and 50 mW/m2 in
the eastem Sardinia shelf). In the peninsular Italy, the heat
flow values indicate two maxima corresponding to recent
volcanic activity in Tuscany and in the Campania margin
(Palinuro area).
Gravimetry (Morelli, 1970; Colombi et al., 1973) indi-
cates the existence of two positive highs (more than
200-250 mgal) corresponding to the Magnaghi, Vavilov and
Marsili areas. Southward, the gravimetrie values decrease
regularly with a minimum corresponding to the centrai part
of Sicily (between Oand -100 mgal in the Caltanissetta Ba-