Strike-slip fault-propagation cleavage in carbonate rocks: the Mattinata Fault Zone, Southern Apennines, Italy

Disjunctive, spaced solution cleavage in carbonate rocks is genetically ass ociated with the propagation of the left-lateral, strike-slip Mattinata Fau lt in the Gargano Promontory, Italy. Typical cleavage development is restri cted within the 200-300-m-wide fault zone, which is bounded by virtually un fractured wall rocks. The cleavage consists of sub-parallel solution surfac es, which are often reactivated as sheared solution planes. Geometrical and kinematic relationships exist between the fault and the associated cleavag e planes, thus: (1) cleavage-fault intersection lines lie parallel to the f ault and the sheared cleavage rotational axes and (2) the cleavage-fault an gle is almost constantly equal to 40 degrees. A model for the development o f the Mattinata Fault is proposed in which the cleavage surfaces are interp reted as fault-propagation deformations. Cleavage nucleates as solution pla nes at the front of the advancing fault as the result of stress concentrati on in this region. Two distinct, time-sequential processes are shown to ope rate during the fault propagation: (1) typical millimetre- to centimetre-sp aced solution surfaces form in the distal tip zone of the advancing fault p lane; (2) as the tip advances, the fault plane breaks through the cleavage as minor shear displacements reactivate some of these nascent surfaces. The se observations may prove useful in understanding mechanisms for fault-cont rolled enhanced/reduced permeability and fluid pathways. (C) 1999 Elsevier Science Ltd. All rights reserved.