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RHEGMATIC-LIKE BASINS IN SICILY 9
Catania Foredeep", connecting to the Malta escarpment. and NE-SW trends cut the E-W trending North Sicily
This trough, filled by Plio-Pleistocene sequences, can be in- Thrust Belt (Ghisetti & Vezzani, 1977). The latter fault sys-
terpreted as a graben-like structure located between the Cal- tems merge along the E-W trendin~ transcurrent systems
tanissetta Basin and the Hyblean Plateau. and are interpreted in this paper as regional trending associ-
ateci Riedel systems. The main NW-SE and NE-SW trend-
Finally, the Ragusa zone is characterised by another ing strike-slip fault-riedels, mostly outcropping in Northern
right-lateral transcurrent fault system of regional signifi- Sicily (Figs. 7A, 8A-B-C-E, 13), stretch and/or truncate the
cance. This is evidenced by sheaves of faults bounding a previous compressive thrust imbricates, and ramp anticlines
N-S trending master mechanical discontinuity, interpreted ofthe Sicily Chain.
as associateci large-scale riedels. The Ragusa fault runs par-
allel to another fault system located in Syracuse, extending In Western Sici1y, the most important outcropping E-W
southwards to the Malta-Medina areas. trending transpressional structures have field evidences in
the Kumeta Mt. and Busambra Mt. areas, where it is possi-
EXTENSIONAL TECTONICS ble to recognise the described large-scale ramp anticlines
cut by subsequent high angle reverse faults that have estab-
Along the Northem and Eastern Sicilian coastal areas, a lished some asymmetrical positive flower structures (Fig.
widespread occurrence of hangingwall tilting low-angle 7A). These structures, which involved a previous strongly
norma! faults (LANFs, Figs. llA,B,C and 12) with the Tyr- deformed substrate (Trapanese domain-derived sequences),
rhenian vergence, cutting the strike-slip fault systems, has are interpreted as a shallow evidence of deep shear zones,
been observed. These LANFs cut the E-W trending tectonic related to the westemmost Moho vertical discontinuities that
edifice, creating a large extension and increasing the accom- have produced associateci shallow riedels (see Fig. l). East-
modation space in half-grabens and in small basins located wards, a local change of direction might have determined a
between the main tilted blocks. number of connecting transtensile structures related to a tor-
sional deformation and an overprinting of large-scale rheg-
Offshore, a progressive eastward decrease in Pliocene matic-like geometries in the Caltanissetta Basin auctorum
package thickness, and an increase in Pleistocene thickness, (Fig. 13). This is shown in Fig. l O, where the en-echelon ge-
can be observed (geologica! interpretation of multichannel ometries could indicate the existence of an E-W trending
high-resolution seismic lines, Fig. 12; Wezel et al., 1981; structural line and might be interpreted as the shallowest
Sartori, 1990). evidence of a buried right-lateral transcurrent fault system
affecting the western subsurface prolongation of the Hy-
REGIONAL SIGNIFICANCE blean Foreland below the Gela Thrust System and the Meso-
OF NEOTECTONIC FIELD DATA Cainozoic deformed substrate (Sicanian domain). lt is likely
that this trend extends westwards in the Sciacca area.
The widespread presence of post Messinian-Pliocene
thrusting in the Northern Sicily Chain leads to the following Northwards, the Caltanissetta Basin is bordered by an
considerations: important right-lateral strike-slip fault system having a re-
giona! E-W trend (Kumeta-Alcantara and Alia-Malvagna
- The recognised geometries appear comparable to the !ines of Ghisetti, 1979a and Ghisetti & Vezzani, 1982). The
tectonic style characterising the Southem Sicily and its off- Kumeta-Alcantara and Alia-Malvagna tectonic lineaments
shore (Bianchi et al., 1987; Argnani, 1993 and literature bound the Northern Sicily coastal area which, during the
therein; Catalano et al., 1993a, b), where the so called "Gela Plio-Pleistocene, was affected by a very strong uplift (Ghi-
Nappe" outcrops; setti, 1979b).
- the thrust sheets that fonn the Gela Nappe, piled up The E-W trending transcurrent buried and emergent
since the Middle Pliocene, are prevalently made up by Nu- faults (and the associated NE-SW and NW-SE trending
midian and Sicilidi sequences and by Late Miocene-Early synthetic and antithetic riedels) found in western and eastern
Pleistocene deposits (AGIP well data of Pozzillo l and Sicily, may be interpreted as intraplate migrating shear sys-
Manfria 1), and thrust over the Pleistocene sequ~nces in the tems related to the NW-SE-directed Tyrrhenian spreading
southem offshore areas. "deep" Pliocene horizons thrusted and to the adjacent Ionian subduction complex (Ghisetti &
by Mesozoic carbonates are also known in the Western Sic- Vezzani, 1981 b). Locally uneven trend of these systems
ily (e. g. Cammarata well). could have produced flower structures (e.g. Kumeta and
Busambra Ridges), neotectonic axial culminations (e.g.
Thus, the analysed Nebrodi Mt. area appears to form the Castelvetrano and Sciacca Ridges), structural depressions
innermost portion of the outcropping Gela Nappe and, ac- derived from torsional deformations (e.g. Caltanissetta Ba-
cording to Ghisetti & Vezzani (1982), represents the shal- sin) and/or pull-apart offshore basins (e.g. Pantelleria Rift,
low expression of the generai reactivation of the Eastem Medina Graben, etc.).
Sicily Chain due to deep compressional mechanisms related
to the late-collisional involvement of crustal levels, as also
proved by the geophysical data of Schutte (1978).
Also, in Northern Sicily, severa! neotectonic disconti-
nuities related to the Tyrrhenian dynamics are located, cut-
ting the post-Messinian thrust surfaces. The neotectonic
fault systems (mostly with strike-slip kinematic indicators)
related to the Tyrrhenian stretching, showing E-W, NW-SE
