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320 E . TAVERNC:LLI E T ALI!

levels (e.g. CONSTENIUS, 1996), and the evolution of col-    Maghl·ebide belt, in the footwall of the Calabro-P eloritani
lapsed thrust systems has been var·iously reproduced         crystalline Units, are the Sicilide, Panormide and Imer ese
through analogue physical modelling (FACCENNA et alii,       Units, that we collectively indicate as !Imer Units (fig. la;
1995), providing sound geometrica! and kinematic con-        CATALANO & D'ARGENIO, 1982). These units are thl·ust
s t r a i nts.                                               onto m ore external tectonic slices, that we indicate as
                                                             Outer Units. The originmy superposition relation ships
     Geologists have long compared the geometry of struc-    among the Im1er and Outer Units have been modified by
tures of varying scales, from microscopic to regiona! (e.g.  a major E-W tr ending dextral strike-slip fault zone, the
see TCHALENKO, 1970) . In particular, the last decades       Mt. Kumet.a-Alcantara Line, that was characterised by a
have seen increasing efforts in documenting similarities     compiex deformati011 histOiy (fig. l ; GHISETTI & VEZ-
and differences among faults and defonnation zones of        ZANI, 1984). The stt·atigraphic sequences of the Outer
d ifferent sizes (e.g. see ARBOLEYA & ENGELDER, 1995).       Units consist of Mesozoic-Tertiary mar·ine sediments.
The results of detailed analyses have shown that many        These d isp lay significant facies and thickness variations,
fault populations exhibit a power-law distribution of fault  that r eflect deposition onto differently subsiding plat-
sizes (WALSH & WATTERSON, 1991 ; PICKERING et alii,          forms (e.g. the Saccense Platfonn) and basins (e.g. the
1995). However, contributions in the field of fault popu-    Sicanian Basin) controlled by syn -sedimentary nonna!
lation analysis have focu sed primar·iiy on the analogies    faults of Mesozoic age (RENDA et a/;;, 1999, and refer-
and differences among structures that resulted from one      ences therein). From Miocene time onwards the sedimen-
single defonnation regime, n ot.ably extensional (CARTER     tmy cover was detached from the underlying basement,
& WINTER, 1995), contractional (WOJTAL, 1994) or stl'ike-    and was tr anslated southwar·ds along E-W trending, shal-
slip (PEACOCK, 1991), whereas evidence for scaling of        low N-dipping tluusts onto the more external Hyblean
structures resulting from negative tectonic inversion, or    foreland, originating the Apennine-Maghr ebide fold-and-
from other superposed defonnations, is rarely provided.      tru·ust belt (CATALANO et a/ii, 1996). According to FINETTI
In this paper we present the results of stluctural analysis
of macroscopic and mesoscopic scale structm·es produced      et alii ( 1996) the southenrmost folds and tluusts of the
by a switch in defonnation regime, from em·Jy contrac-       belt have their westwar·d, onshore continuation in the
tion to late extension. Our examples are derived from a      Egadi Islands (fig. 1). The front of the Gela Nappe is tt·a-
portion of the Sicilian Neogene Apennine-Maghl·ebide         d itionally r egar ded as the boundmy between the Apen-
fold -and-tru·ust belt exposed in the Isle of Favignana, in  nine-Maghl·ebide belt and the H yblean foreland, although
the Egadi Islands (fig. l ; TAVARNELLI et a/ii, 2003).       integrated sub-surface and offshore data indicate that
                                                             moder ate tluusting has also occurred south of it (fig . l ;
                             GEOLOGICAL SETTING              ARGNANI, 1987, and references therein).

     The defonnation hist01y of Sicily and adjacent minor         During Late Miocene, P liocene and Pleistocene times,
islands is characterised by the superposition of different   the fold-thlust architectUl'e of the Apennine-Maglu·ebide
tluust sheets that were detached from distinct paleogeo-     belt has been severely m odified by low-angle and high-
graphic domains of the Mesozoic African passive conti-       angle, E -W trending nonna! fault sets, that were induced
nental mm·gin during the emplacement of the Neogene          by post-orogenic extension (WEZEL, 1985 ; GIUNTA et a/;;,
Apennine-Maghl·ebide fold-and-thrust belt (OGNIBEN,          2000; PEPE et a/;;, 2000). Extensional deformation pro-
1960). Orogenic defonnation occurred under brittle to        gr essively migrated southwards, truncating ancl!or partly
semi-brittle conditions, and was associated with fluid-      reactivating pre-existing, shallow N-dipping tlu·ust sur-
assisted pressure-solution mechanisms (NIGRO & RENDA,        faces.
2002). The uppennost tluust sheets of the Apemli.ne-
                                                                  In the forthcoming sections we report evidence for
                                                             norma! faults that overprint tluusts on two different,
                                                             macr oscopic and mesoscopic scales of observation. Our

Egadi
lslands

         Km                                                  Fig. l - S implifiecl tectonic sketch of
                                                             Sicily ancl acljacent minor islands ,
                                                             show ing the Jocation of the stntc-

                                                             tures analysecl in t his stucly.
                                                             - Schema tettonico semplificato della

                                                             Sicilia e delle isole minori circostanti,

                                                             nel quale è indicata la locali==a=ione
                                                             delle strutture desCI'itte in questo stu-

                                                             dio.
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