Structural Analysis and Micro-Deformations Syn- to Post-Folding of the Visean limestones

Abstract

The Allochthonous Visean limestones of the Eastern part of the Moroccan central massif, occurring along the front of the Jebel Bou Khmis thrust fault, between Mrirt and Amghass, have undergone a structural and microtectonic study, aiming to study fracturing and its relationship between folding. The microtectonic studied sites were selected in different folds and in different parts of the same fold (long and short limbs and in the hinge) in order to study the relationship with fold geometry and fracturing, and to show the control of the facies and its importance in the genesis of fracture networks. The sub-vertical fractures family appear to be anterior to sub-horizontal once. They correspond to the first deformation accompanying the first shortening phases during the layer parallel shortening (LPS). The horizontal fractures were developed by accommodating of the fold when extending vertically during the amplification of the hinge. These three fracture families are syn- to post major folding phase that generated penetrative NE-SW oriented cleavage. The same results were obtained from microscopic study of thin sections, selected among oriented limestone samples, within oolites, calcite crystals and fluid inclusions.