From Jurassic extension to Miocene shortening: An example of polyphasic deformation in the External Dorsale Calcaire Unit (Chefchaouen, Morocco)

- A structural analysis of Liassic part of the External Dorsale Calcaire is provided.
- Normal faults and veins result from extension related to the Jurassic rifting.
- Pre-orogenic structures were successively deformed in a passive manner.
- Orogenic deformation consists of two main shortening stages.

Liassic rocks of the External Dorsale Calcaire succession, cropping out in the northern Rif close to Chefchaouen city, host pre-orogenic structures, such as normal faults, veins and fractures, resulting from extension related to the Jurassic rifting of the Neotethys Domain. The successive inclusion of these rocks in the orogenic wedge, which mainly occurred in the Miocene time, deformed the most of pre-orogenic structures in a passive manner, without an overall reverse reactivation. The orogenic deformation includes two main stages; the first tectonic pulse, which occurred during the Burdigalian-Langhian interval, was characterized by a NE-SW shortening (in the current coordinates) and recorded by folds, thrust and back-thrust faults. During this stage the carbonates of the External Dorsale Calcaire tectonically covered the Predorsalian succession, producing, in the thrust front, a SW-verging regional fold. The second orogenic deformation, consisting of a NW-SE shortening, was expressed by thrust faults and related folds both verging to NW and SE, which probably occurred in the Late Miocene-Pliocene time.