CONTEMPORANEOUS THRUSTING AND LARGE-SCALE ROTATIONS IN THE WESTERN SICILIAN FOLD-AND-THRUST BELT

In the western Sicilian fold and thrust belt, large clockwise rotations of allochthons occurred during late Cenozoic contraction of part of the southern Tethyan margin. The magnitude of rotation decreases stepwise from over 120° in the upper sheets, lying on the north coast of Sicily, to no appreciable rotation in the frontal portion of the belt flanking the southern coast of the island. The allochthons are composed of imbricate thrust sheets derived primarily from individual basin and platform assemblages of the old Tethyan margin. Paleomagnetic and structural data indicate that the rotation of the allochthons was accommodated by coherent torsional displacements on relatively low‐angle detachment surfaces. Timing relations for the imbrication history of the Sicilian fold and thrust belt are derived from stratigraphic overlap and local involvement of sediments deposited in a series of foreland and piggyback basins. The locus of deposition within successive foreland basins first migrated easterly then southerly during progressive deformation in the orogen. Imbrication began in the early Miocene (Burdigalian‐Langhian) and continued at least through the early Pleistocene and appears to be continuing today. Rotation is related to thrusting and accompanies a 70° change in the tectonic transport direction from easterly to southerly. Easterly striking, right‐oblique transpressional faults and associated northeasterly trending folds postdate thrust sheet rotation in the interior of the thrust belt and were active contemporaneously with south‐directed thrusting in the foreland region. Pleistocene and possibly older (late Pliocene?) extension strongly modified the older thrust morphology along the Tyrrhenian coast of northwestern Sicily, with the development of down‐to‐the‐north listric normal faults. The extensional structures apparently are related to the opening and subsequent deformation of the Tyrrhenian Sea to the north. Copyright 1990 by the American Geophysical Union.