Structural evolution of the Moroccan Central High Atlas Syncline-Topped Anticlinal Ridges: Insights from micro-structural analysis of Tirrhist and Anemzi ridges
Authors: Skikra Hamza , Amrouch Khalid , Ahechach Youssef , Ouabid Muhammad , Soulaimani Abderrahmane , Raji Otmane , Bodinier Jean-Louis 
Published: March 2021

&lt;p&gt;The Moroccan High Atlas mountain range is an aborted Mesozoic rift basin that was moderately shortened during the Late Cretaceous&amp;#8210;Cenozoic inversion. The range is currently featured in its central part by the presence of conspicuous S-shaped open gentle synclines where Middle Jurassic strata crop out, with sub-horizontal bottom, separated by 15-to-80-km narrow faulted anticline ridges with two distinct directions: ENE and NE. The tight anticline ridges are cored by Triassic continental red-beds intruded by the CAMP basalts and subsequently by Upper Jurrasic&amp;#8210;Lower Cretaceous alkaline magmatism. Regional cleavage with very low-grade anchi- to epi-zonal metamorphism are depicted along several structures of the High Atlas, particularly the NE-trending anticlines. The sedimentary layers thickness, on the other hand, gets thinner towards the faulted anticlines with the development of intraformational truncations. The structural history of the High Atlas syncline-topped anticlinal ridges remains a controversial matter. Any attempt to reconstruct the evolutionary process of such folded structures must take into consideration the following circumstances:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;After a Triassic rifting episode followed by the establishment of Liassic carbonate platform, the High Atlas basin underwent a wide spread exhumation event at the time interval between the Middle Jurassic and Lower Cretaceous leading to the deposition of continental detrital series and sedimentary hiatus;&lt;/li&gt;
&lt;li&gt;The upward motion was accompanied with the emplacement of alkaline magmas in the Central High Atlas;&lt;/li&gt;
&lt;li&gt;A complex halokinetic history characterizes the Central High Atlas salt province during both pre-orogenic and orogenic stages;&lt;/li&gt;
&lt;li&gt;During the Late Cretaceous&amp;#8210;Cenozoic, the High Atlas experienced a moderate crustal shortening which was focused essentially within the range&amp;#8217;s borders;&lt;/li&gt;
&lt;/ul&gt;&lt;p&gt;In order to bring new insights to the structural history of the High Atlas folded structures, a structural investigation was carried out in Tirrhist and Anemzi ridges. In each station, fractures measurements were taken, and oriented samples were collected for micro-structural analysis. First paleo-stress inversion in some stations reveals the presence of pre-folding bedding-parallel maximal horizontal stress oriented NE to NNE. For a deep analysis of pre syn and post-folding stresses history, we use a calcite stress inversion technique, namely Etchecopar&amp;#8217;s method, to unravel the paleo-stresses orientations and to quantify the differential stresses during the different episodes of deformation. The present work is a preliminary attempt to quantify tectonic stresses in the hinterland of an arguably weakly deformed orogenic belt.&lt;/p&gt;