Page 11 - Corti_2006

Coexisting geodynamic processes in the Sicily Channel 93

jor thrust system parallel to the moving wall and developing at
~10 cm away from it. Extensional deformation localized in the
correspondence of the basal VD, with the development of a cen- A VD A
tral depression orthogonal to the moving wall. This depression
was bordered by normal faults, clearly evident close to the fixed
wall of the deformation apparatus (Fig. 11B). For increasing de-
formation (Fig. 11C), thrust faults propagated toward the fore- G H
land portions of the model, with the development of a second
thrust system ~18–20 cm from the moving wall. This thrust sys-
tem displayed an evident curvature in correspondence to the
central depression. Further extension was accommodated by in- E F
creased throw along major normal faults and by subsidence
within the central graben. B
In the latest stages of deformation (compression 9.5 cm; C D
extension 2 cm; Fig. 11D) major thrust systems were charac- VD
terized by a complex arrangement resulting from the interac- B
tion with extensional structures. In particular, this interaction is
evidenced by (1) curvature of thrusts, (2) development of thrust A B
splays corresponding to the central depression, and (3) a lower
amount of rift subsidence in the regions affected by compres-
sive deformation.
The complex fault pattern resulting from the contempora-
neous compression and extension is also seen through analysis
of model cross-sections (Fig. 12). Away from the central VD, no
extensional structures developed, and deformation was taken up
by a regular array of thrusts and back-thrusts (Fig. 12, section
AB); conversely, close to the fixed wall in the regions not af- C D
fected by compressive deformation, the cross-section shows the
main graben above the VD, bordered by steep normal faults
(Fig. 12, section CD). In the central part of the model, the cross-
sections display the complex patterns of superposition between
compressional and extensional structures (Fig. 12, sections EF
and GH). In summary, interaction between thrust systems and
normal faults gave rise to a complicated 3-D geometry of main
VD
structures.
E F
COEXISTING GEODYNAMIC PROCESSES
IN THE SICILY CHANNEL

Structural and geophysical data suggest that the structural
pattern of the northwestern side of the Sicily Channel is charac-
terized by a northeast-southwest-striking accretionary prism
VD
composed of thrusts and folds and a system of northwest-south- G H
east-trending normal faults and grabens. Analysis of seismic
profiles suggests that both thrusts and folds related to the accre-
tionary prism and normal faults actively deform the seafloor; the
thrust-sheets crosscut the almost orthogonal rift-related normal
faults and vice versa. Although previous models (e.g., Giunta et
al., 2000) described coeval compressional and extensional
structures related to an east-west-trending simple shear system
in the Sicilian-Maghrebides Tyrrhenian back-arc margin, the VD
geometry of extensional structures in the Sicily Channel (almost
Figure 12. (A) Top-view photo showing locations of cross-sections in
orthogonal to and in the foreland of the thrust system) and the panel B. (B) Analogue modeling results: photos of cross-sections.
location of the rift far away to the southeast of the accretionary VD—velocity discontinuity. Rulers are in centimeters.