Unexpected Jurassic to Neogene vertical movements in ‘stable’ parts of NW Africa revealed by low temperature geochronology

Abstract

In Morocco, it is generally considered that post‐Hercynian vertical movements were limited to the Atlas system, the passive continental margin and the Rif. Apatite FT and He ages from the Moroccan Meseta (Rehamna and Zaer Massif) document instead two episodes of subsidence and exhumation in Jurassic‐Early Cretaceous and during the Late Cretaceous to Neogene. The Meseta subsided to >3 km depth during the Late Triassic to Middle Jurassic and was exhumed to the surface before the Late Cretaceous, during the rift and post‐rift stages of Central Atlantic opening. Erosion of the exhuming rocks is responsible for a thick package of terrigenous sands found in the Moroccan offshore and elsewhere along the NW Africa margin. About 1 km of subsidence affected the Meseta during the Late Cretaceous to Eocene. During the Neogene, these areas were brought back to the surface in association with bimodal folding with wavelengths of 100–150 km and >500 km.

Spectral analysis of the gravity and elevation along the western Africa–Eurasia plate tectonic limit: Continental versus oceanic lithospheric folding signals

“…Moreover, widespread deformation would facilitate the transmission of the fold trend along the northern part of the African Atlas which in turn may explain the high altitude reached by the Atlas Mountains (de Lamotte et al, 2009;de Vicente and Vegas, 2009;Ghorbal et al, 2008;Teixell et al, 2003).…”

Post-rift vertical movements and horizontal deformations in the eastern margin of the Central Atlantic: Middle Jurassic to Early Cretaceous evolution of Morocco

“…Indeed, Mesozoic ages and t-T paths comparable to the ones discussed above have been obtained from rocks from the Jebilet Hills N of Marrakech to the Rabat area (e.g., Ghorbal et al 2008;Saddiqi et al 2009;Barbero et al 2011). Subsidence along the Central Atlantic margin to the N of the EssaouiraAgadir basin has been quantified and modeled by Gouiza et al (2010) Early Cretaceous (100Ma) Fig.…”

“…The recent discovery of Late Triassic to Early Cretaceous km-scale vertical movements, subsidence and then exhumation, affecting substantial parts of Morocco which had hitherto been considered as stable (Ghorbal et al 2008;Saddiqi et al 2009;Barbero et al 2011;Ruiz et al 2011) represents a major development in Moroccan geology, opening new horizons for understanding the Mesozoic tectonic evolution of NW Africa. The exhumation component of these movements, in particular, is remarkable as it took place after the appearance of oceanic crust in the Central Atlantic, that is, during its passive margin development (e.g., Sahabi et al 2004;Gouiza et al 2010).…”

“…In the recent past, a number of studies by different groups (e.g., Ghorbal et al 2008;Saddiqi et al 2009;Ghorbal 2009;Barbero et al 2011;Ruiz et al 2011) have concluded that rocks of the Meseta of N Morocco, the High Atlas and parts of the Anti-Atlas, have experienced [1 km of exhumation during Middle Jurassic to Early Cretaceous times. More low-temperature geochronology (low-T) work is ongoing on samples from the Anti-Atlas and areas of southern Morocco ) and will undoubtedly result in new relevant information.…”

The Upper Jurassic-lower Cretaceous Siliciclastic System in the Morocco Offshore - Prevenance, Transport and Deposition

“…The kinematics of exhumation in this northern region is fairly well documented by a significant number of low-temperature geochronological studies (Bertotti and Gouiza, 2012;de Lamotte et al, 2009;Ghorbal et al, 2008). Following the Variscan orogeny, the entire region was peneplained and began subsidence possibly in relation with Central Atlantic rifting allowing for the deposition of Triassic to Jurassic clastics and carbonates.…”