Analysis of fracturing at the front of the massif gravity aquifers central Moroccan and relation with the folding at Jebel BouKhmis (Eastern part of the Central Massif, Morocco)

Abstract

The Moroccan Massif Central Hercynian (MCHM) has been the subject of numerous geological studies, and continues to arouse the interest of geologists, given the diversity of ages and outcrops it offers and the richness of its landscapes, from the edges of the Atlasic Alpine ranges to the Atlantic coast. The eastern part of this massif constitutes a segment of the Moroccan Hercynian chain, with allochtonian Paleozoic series, extending from the Ordovician to the Namurian. The front of these slicks is formed by the devono-carboniferous carbonate formations set up in a context of for-country basin in compression, during the Upper Viséen and the Namurian–Westphalian. These formations align in an NNE-SSW direction and appear to overlap with the targeted flyschoid series. Paleozoic formations throughout this region are structured in NE–SW-oriented anticlinals and synclines from the major phase of Hercynian orogeny, known as the Namurian–Westphalian phase. The microtectonic measurements have thus interested the flyschoid series (alternation Grés- pelitic), the metric sandstone bars and the massive and stratified carbonate series. In the flyschoid series, the fractures analyzed mainly correspond to the inverted microfaults at Vergence West, determining the fish-tail structures affecting the sandstone banks and accompanying. The main folding. In contrast, in metric sandstone bars and in carbonate units, fracturing is more intense and shows at least three main families, two sub-vertical families, transverses to the fold axis, and a sub-horizontal axial family. The families of sub-vertical fractures appear to be anterior to sub-horizontal fractures. They appear to correspond to the first brittle deformations accompanying the early shortening phases during the parallel shortening layer (PSL), the horizontal fractures developed by accommodation of the fold during the extension Vertical and the amplification of the hinge. These three fracture families are posterior to the major folding phase that generated synschisteux folds at schistosity penetrative oriented NE–SW. These fractures seem to accompany the ultimate folding phases or they are contemporaneous to the last brittle phases affecting the Moroccan Hercynian chain. Microscopic study of about 50 thin sections on oriented samples, made in Visean carbonate facies, reveals microfractures and microshears that confirm the presence of penetrative deformation in these rocks. A work of quantification of this deformation especially in the oolitic limestone facies shows that these oolites are flattened and sheared according to the NW–SE shortening.