Page 9 - Corti_2006

Coexisting geodynamic processes in the Sicily Channel 91

× 45 cm × 6 cm were built over the basal metal plate of the de- internal friction of ~39°. Experiments were conveniently scaled
formation apparatus; two orthogonal stepper motors controlled such that 1 cm in the models represented 1 km in nature, imply-
by a central unit were used to drive compression with contem- ing that the models simulated a 5 km–thick layer of upper-
poraneous orthogonal extension (Fig. 10). In particular, short- crustal rocks in nature. Because the brittle behavior of sand is
ening of the models was obtained by movement of a mobile wall strain-rate independent, scaling for velocity was not critical in
at a constant velocity of ~5 cm/h up to ~10 cm of compression these experiments. However, in order to closely mimic the nat-
(~25% bulk shortening). Coeval extension was imposed on the ural example, compression was driven about five times faster
models by pulling a thin acetate sheet at the base of the model, than extension.
creating a central velocity discontinuity (VD) parallel to the di-
rection of compression (Fig. 10). Extension was applied at 1 Model Results
cm/h up to 2 cm of stretching (~5% bulk extension).
Models consisted of a single quartz sandpack simulating the Figure 11 portrays the evolution of model SCh 03, which is
brittle behavior of upper-crustal rocks in nature. The sand had a taken as representative of the whole experimental series. For a
–3
density of ~1500 kg m , a cohesion of ~65 Pa, and an angle of low amount of deformation, compression was taken up by a ma-

A Compression

at 5 cm/hr
Mobile wall

22 cm

VD 40 cm 20 cm
Extension A B
at 1 cm/hr Figure 10. (A) Experimental set-up and
(B) model rheology. VD—velocity dis-
continuity. See text for details.

45 cm

Basal acetate sheet

Fixed wall
B
A B

6 cm Sand

Basal acetate sheet VD
22 cm