Page 8 - Tondietall2015

Italian Journal of Geosciences Accepted manuscript

FAVIGNANA SITE
The Favignana carbonate grainstones are affected by conjugate strike-slip compactive shear
band-based faults striking NW-SE and N-S, respectively. These faults are characterized by dip
angles ranging from 50° to 90° (TONDI et alii, 2012; fig. 4a). The NW-SE striking faults are
characterized by a right-lateral strike-slip kinematics, whereas the N-S striking ones by left-lateral
one. These conjugate faults show mutually crosscutting relationships, indicating coeval
development. Some faults parallel to the strike slip sets show a dip-slip (normal) component of
motion, and are therefore classified as normal faults. The aforementioned faults formed under a
minimal overburden loading; the maximum burial depth experienced by the Lower Pleistocene
carbonate grainstones is, indeed, estimated to be not in excess of 50 m (ABATE et alii, 1995, 1997).
Orientations and kinematics of the two sets are consistent with those of the most recent faults of
NW Sicily, whose kinematics are compatible to the current regional stress field, which is
characterized by a NW-SE oriented, horizontal compression direction (TONDI et alii, 2012 and
references cited therein). The studied fault zones have a thickness varying from 0.1 to 1 meter
(generally 10-30 cm); they encompass compactive shear bands with continuous slip surfaces, and
the associated cataclastic fault rock (fault core) overprinting older zones of bands. Individual faults
are 8-100 m long and accommodate from 10 to over 200 cm of displacement. Along the faults,
when displacement reaches 20-30 cm, a continuous discrete slip surface is recognizable (fig. 2a). A
greater number of compactive shear bands occur in the damage zones of faults with larger slip.
Compactive shear bands are narrow tabular zones easily recognizable in the field because of their
positive relief with respect to the host-rock, due to their increased resistance to weathering (AYDIN
& JOHNSON, 1978). In the study area the single compactive shear bands are typically 0.3-1 m long,
4-6 mm thick.
Fault cores are narrow, red colored zones of reduced grain size and including striated slip
surfaces. In outcrop, these zones commonly show a negative relief.