Syn-thrusting polygonal normal faults exposed in the hinge of the Cingoli anticline, northern Apennines, Italy

The Cingoli arcuate anticline is part of the Apennines fold-thrust belt in Italy. The anticline nvolves sedimentary carbonate strata generally affected by syn-thrusting contractional tructures such as bed-normal pressure solution seams, folds, and reverse faults. An xception is constituted by an outcrop in the anticline hinge, where sub-horizontal arbonate and chert beds are affected by joints and intraformational short normal faults. hese faults are poorly-systematic and conceivably polygonal in map view. They cut hrough the carbonate beds while usually stop against the chert layers that are bent nd extended along the faults themselves. At the fault tips, the displacement is generally ransferred, via a lateral step, to an adjacent similar fault segment. The fault surfaces are ften characterized by slickolites, greenish clayey residue, and micro-breccias including hert and carbonate clasts. Fault displacement is partly or largely accommodated y pressure solution. The faults, in effect, are usually accompanied by bed-parallel ressure solution seams in the two contractional quadrants located at the present or ast fault tips. The pressure solution features fade away departing from the faults. This vidence and others are analytically explained with fault tip stress distributions. The faults re interpreted as polygonal normal faults syn-tectonically (syn-thrusting) nucleated in esponse to multi-directional stretching processes occurred at the Cingoli triply-folded nticline extrados. The faults then grew through a four-stage process: (1. stop) the aults stopped at the competent chert beds; (2. shrink) faulting produced shrinkage pressure solution) of carbonate beds at the fault compressive tips; (3. shrink and step) he faults stepped laterally at the competent chert beds; (4. shatter) the chert beds were hattered along the fault surfaces. The case presented constitutes the first reported one f syn-thrusting non-diagenetic polygonal normal faults. i s e c T t a t o c b p p e a r a f ( t s o