Deciphering the tectonic complexity of the Central High Atlas Mountains using brittle deformation mesostructures and calcite mechanical twinning analysis

Abstract

<p>Located in the western segment of the intracontinental Atlas system, the Moroccan Central High Atlas is a NE-SW to ENE-WSW-trending Fold-and-Thrust Belt that is formed during the Cenozoic Alpine orogeny by a positive inversion of Triassic-Jurassic basin. It is structurally distinguished from the other segments of the Moroccan High Atlas orogenic belt by the occurrence of S-shaped ENE-WSW oriented tight anticlinal ridges bounding wider synclines. The elongated ridges core disordered association of plutonic rocks, Liassic carbonate and Late Triassic arigilites, whilst the wider synclines are filled by thick Jurassic series with minor magmatic manifestations expressed by mafic and felsic dikes. The origin of these structures has been ascribed to pre-inversion wrench tectonics with significant compressive component whereas they have been attached to post-rift rift block tilting and or salt tectonics in an alternative view. Characterizing the paleostress history is thereby a crucial matter to unravel the structural evolution of these structures. In order to bring new insights into the actual understanding of the Central High Atlas post-rift structural history, we reconstruct the paleostress tensors preserved in the folded Jurassic series of Anemzi and Tirrhist regions based on brittle deformation structures together with calcite twins stress inversion. The preliminary results highlight the presence of pre-folding layer parallel maximum horizontal stress during three stages: E-W to ENE-WSW, NNE-SSW and NW-SE compressions. Local extensional stress features are observed essentially near diapiric structures and the exhumed magmatic intrusions. The latest structural stage is featured by a post-folding NW-SR compression likely related to the recent phases of the Alpine orogeny.</p>