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RHEGMATIC-LIKE BASINS IN SICILY
structures involve the deformation at least the sequences of
1.4 Ma in the Eastern Sardinia Shelf. Also, the seismic line
14D shows the presence of extensional tectonics during the
Early Pliocene, followed by an inversion tectonic event ac-
tive unti! 1.4 Ma, that produced the NW-SE trending struc-
tures in the Sicily Straits.
The seismic line 14E, from the Centrai Tyrrhenian,
shows severa! angular unconformities bounding groups of
reflectors. Particularly, in the depositional sequences
bounded by the 1.4 and 0.8 isochrones, it is possible to as-
sume the presence of extensional tectonics. The 1.4, 0.5 and
probably the 0.2 sequence boundaries indicate compression.
A very fast subsidence between 0.5 Ma and 0.2 Ma, and the
intrusion of basaltic dikes, indicate extensional tectonic
stages.
The seismic lines 14F and 14G, from the Hyblean sub-
merged sector and the Gela Gulf respectively, show two
NE-SW trending positive flower structures active since the
Late Miocene, involving sedimentary sequences post- 1.4
Ma.
The above examples allow to synthesise the structural
setting ofthe peri-Tyrrhenian submerged areas, often repre-
sented by transpressive and/or inversion geometries, syn-
chronous with the "expansion" and "oceanization" of the
centrai Tyrrhenian areas. Thus, the deformational phases
recognisable in the submerged areas, as well as in the Sicily
mainland, are alternatively expressed by transpressional and
extensional tectonics. The age of deformations fits well to
the deformational history as proposed by severa! authors
(e.g. Agate et al., 1993; Catalano et al., 1993a, c):
- extension pre-4.8 Ma;
- compression until3.0 Ma;
- extension between 3.0-2.4 Ma;
- inversion (transpression) between 2.4-1.4 Ma;
- extension between 1.4-0.8 Ma;
- compression at 0.8 Ma;
- extension after 0.5 Ma.
Is possible to recognise the overlap of extensional and
compressional/transpressional tectonics that have produced
severa! inversion geometries.
STRUCTURAL SUMMARY OF MARINE
DATA
The main structural features of submerged areas sur-
rounding Sicily, derive from an assemblage of published
and unpublished seismic data. They include:
I) a western sector (between Sardinia, Egadi Islands
and Tunisia) characterised by a prevalent NNW-SSE to
NW-SE trending right-lateral transcurrent (locally transten-
sile) fault system (''Egadi Fault" of Finetti & Del Ben,
I986; and its northward prolongation), extending from the
eastern Sardinia shelf to the Sicily Straits. The megariedels surrounding Sicily, and the comparison with deformational
associateci with this mega-structure determine severa! struc- events in the mainland, indicate that the overall Tyrrhenian
tural depressions (grabens and half-grabens) filled by Plio-
Pleistocene sequences. Southwards, this faults system di-
vides:
2) the Pelagian Block, where transpressive movements
characterise the Eastern Tunisia (Zaghouan Fault), from:
13
3) the rhegmatic-like basins of the Pantelleria-Linosa
area (Baumann & Reuther, I985; Celio et al., 1985a, b;
Reuther & Eisbacher, 1985; Boccaletti et al., 1987; Celio,
1987; Reuther, 1989). The Southern Sicily offshore is char-
acterised by a rifting process (Pantelleria, Linosa) expressed
by the NW-SE trending pull-apart basins, interpreted as the
southeastward continuation of the Egadi Fault. The South-
ern Sicily offshore is also characterised by the NE-SW
trending transpressive structures, interpreted as synthetic
mega-riedels;
4) the Eastern Sicily offshore, characterised by a very
important N-S trending structural line (Malta Escarpment)
dividing the Hyblean-Malta-Medina Foreland (Il!ies, 1981;
Celio et al., 1984) from the Ionian subduction complex
(Ionian microplate; Biju-Duval et al., 1982);
5) the Northern Sicily offshore characterised by a mix-
ing of extension and transpression processes during the late
Plio-Pleistocene that detennined severa! small basins and
inversion structures (Tricart et al., 1990);
6) the Tyrrhenian area s.s., where the overall stretching
and subsidence is coupled by the effects of the above de-
scribed tectonic events.
SYNTHESIS OF THE REGIONAL
STRUCTURAL SETTING
A review of deep geophysical data, deep well data, un-
published field survey data, seismic ref1ection profiles and
published seismic data, makes it possible to distinguish the
following tectonic domains for the Centrai Mediterranean:
l) The Southern Tyrrhenian Margin, characterised by
NW-SE to E-W trending strong extension (represented on
land by the E-W trending LANF systems) and a NW-SE
trending right-lateral strike-slip displacements. Generally,
the dip-slip system cuts the other one;
2) the Sicily mainland, characterised by:
a) the most extemal ofthe thrust complex (Sicanian and
Gela Thrust Systems) emplaced from the Late Pliocene to
the Pleistocene;
b) a prevalentE-W trending emergent and buried active
right-lateral transcurrent faults with associated Riedel sys-
tems;
3) the Southem Sicily offshore, characterised by rifting
processes;
4) the Eastem Sicily offshore, characterised by the ac-
tive Ionian subduction complex.
The illustrateci tectonic domains are consistent with the
mode! shown in Figs. 15, 16 and 178.
DISCUSSION
The recognised tectonic history in the submerged areas
opening is characterised by severa! tectonic stages which are
related to the time changes of regiona! stress fie ld, as a result
of geodynamic processes in the Mediterranean area. The
change of stress fie ld indicates that the driving forces ("mo-