Page 1 - TheEffects-post-orogenic-extension-different-scales –Tavarnelli-2003

The effects of post-orogenic extension on different scales:
an example from the Apennine–Maghrebide fold-and-thrust belt,
SW Sicily

Enrico Tavarnelli,1* Pietro Renda,2 Valeria Pasqui3 and Mariano Tramutoli3

1Dipartimento di Scienze della Terra, Universita` di Siena, Via Laterina 8, 53100, Siena, Italy; 2Dipartimento di Geologia e Geodesia,
Universita` di Palermo, Corso Tukory 131, 90147, Palermo, Italy; 3Regione Basilicata, Via Anzio, 85100, Potenza, Italy

ABSTRACT scales, from regional to mesoscopic, in the south-western
portion of Sicily and in the adjacent Isle of Favignana.
Many structures produced under one single deformation The recognized analogies in the geometry of these composite
regime, namely extensional, contractional or strike-slip, exhibit structures may provide a key for the interpretation of the
remarkable geometrical analogies when analysed at different features of regional structures, whose deep geometry is
scales. By contrast, field examples that illustrate the scale often poorly constrained. Moreover, comparison of normalized
effects on structures resulting from superimposed deforma- displacements accommodated by contractional and extensional
tions, which were produced under different tectonic regimes, faults of different scales indicates that self-similarity is
are rare. Yet the change from contraction to extension is known not unique to structures produced under single tectonic
to occur often in the most thickened portions of the continental regimes.
crust. The Apennine–Maghrebide fold-and-thrust belt of Sicily
shows many examples of post-orogenic extensional deforma- Terra Nova, 15, 1–7, 2003
tions. Composite structures, resulting from late normal faults
that offset folds and thrusts, are observed at four different

Introduction documenting existing analogies and superposition of different thrust sheets
differences among faults and deforma- that were detached from distinct pal-
Normal faults that offset folds and tion zones of varying scales (e.g. see aeogeographical domains of the
thrusts represent a common feature Arboleya and Engelder, 1995). Many Mesozoic African passive continental
within many orogenic belts, and the fault populations exhibit a power-law margin during the emplacement of the
transition from contraction to exten- distribution of fault sizes (Pickering Neogene Apennine–Maghrebide fold-
sion, known as negative tectonic et al., 1995), and analysis of structures and-thrust belt (Ogniben, 1960). Oro-
inversion (terminology after Williams of varying scales may enable one to genic deformation occurred under
et al., 1989), occurs often during the infer general laws for fault propagation brittle to semibrittle conditions, and
advanced stages of mountain building processes (Walsh and Watterson, was associated with fluid-assisted
(Dewey, 1988). The effects of neg- 1991). Contributions in the field of pressure-solution mechanisms (Nigro
ative tectonic inversion have been fault population analysis have focused and Renda, 2002). The uppermost
unravelled at different crustal levels primarily on the analogies and differ- thrust sheets of the Apennine–Magh-
(Carmignani and Kligfield, 1990; Con- ences among structures that resulted rebide belt, in the footwall of the
stenius, 1996), and the evolution of from one single deformation regime, Calabro–Peloritani crystalline Units,
collapsed thrust systems has been notably extensional (Carter and Win- are the Sicilide, Panormide and Imer-
variously reproduced through ana- ter, 1995), contractional (Wojtal, 1994) ese Units, which we collectively refer
logue physical modelling (Faccenna or strike-slip (Peacock, 1991), but evi- to as the Inner Units (Fig. 1a; Cata-
et al., 1995), providing sound geomet- dence for scaling of structures resulting lano and D’Argenio, 1982). These
rical and kinematic constraints, and from negative tectonic inversion, or units are thrust onto more external
showing that late- or post-orogenic from other superposed deformations, tectonic slices, collectively termed the
extension plays an important role in is rarely provided. In this paper we Outer Units. The original superposi-
the evolution of most thickened por- present the results of a structural ana- tion relationships among the Inner
tions of the continental lithosphere lysis carried out along structures of and Outer Units have been modified
(e.g. see Platt and Vissers, 1989). varying scales produced by a switch in by a major E–W-trending dextral
deformation regime, from early strike-slip fault zone, the Mt
Since the pioneering work by Tcha- contraction to late extension. Our Kumeta–Alcantara Line, which has
lenko (1970), where the geometries of examples are derived from the Apen- undergone a complex deformation
microscopic faults were compared to nine–Maghrebide orogenic system of history (Fig. 1a; Ghisetti and Vezzani,
those of lithospheric fault zones, south-western Sicily, and from its west- 1984). The stratigraphic sequences of
there has been increasing effort in ward continuation in the Isle of Favig- the Outer Units consist of Mesozoic–
nana, in the Egadi Islands (Fig. 1a). Tertiary marine sediments. These dis-
*Correspondence: Enrico Tavarnelli, Dip- play significant facies and thickness
artimento di Scienze della Terra, Univer- Geological setting variations that reflect deposition onto
sita’ di Siena, Via Laterina n. 8, 53100, differently subsiding platforms (e.g.
Siena, Italy. Tel.: +39 (0)577 233 984; fax: The deformation history of south- the Saccense Platform) and basins
+39 (0)577 233 938; e-mail: tavarnelli western Sicily is characterized by the (e.g. the Sicanian Basin) controlled
@unisi.it

Ó 2003 Blackwell Publishing Ltd 1