Post-Variscan evolution of the Anti-Atlas belt of Morocco constrained from low-temperature geochronology

M Gouiza,P Andriessen,R Charton,J E A Storms,G Bertotti

doi:10.1007/s00531-016-1325-0

M Gouiza, P Andriessen + Show 3 more

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https://doi.org/10.1007/s00531-016-1325-0

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Abstract

The Anti-Atlas belt of Morocco extends ENE–WSW, over more than 600 km, from the Atlantic margin in the west to the interior of the African plate in the east. It exhibits Precambrian rocks outcropping as basement inliers and surrounded by marine Ediacaran–Cambrian sequences around the axis of the mountain range. The belt, which has for a long time been interpreted as of Variscan age, is now revealed to have experienced major vertical movements through Mesozoic and Cenozoic times. Thereby, the Anti-Atlas domain appears to be affected by two episodes of exhumation separated by an episode of subsidence. The initial episode occurred in the Late Triassic and led to the exhumation of 7.5–10.5 km of crustal rocks by the end of the Middle Jurassic (ca. 160–150 Ma). The following phase resulted in 1–3 km of basement subsidence and occurred during the Late Jurassic and most of the Early Cretaceous. The basement rocks were then slowly brought to the surface after experiencing 2–3.5 km of exhumation throughout the Late Cretaceous and the Cenozoic. The timing of these episodes of exhumation and subsidence coincides with major tectonic and thermal events in relation with the evolution of the Atlantic and Tethys Oceans, indicating that the effects of their rifting and drifting extended beyond their presumed margins.

Highlights

In Morocco, domains of outcropping Precambrian–Paleozoic basement along the Atlantic rifted margin (e.g., Meseta, Jebilet, Massif Ancient of Marrakech, and Anti-Atlas belt) were always recognized as relatively stable and not experiencing any major post-Variscan vertical movements (Michard 1976; Guiraud et al 1987, 2005)
The obtained pooled apatite fission track (AFT) ages are between 87.5 ± 3.9 and 160.3 ± 6.5 Ma, and the mean track lengths (MTL) are between 12.04 ± 1.53 and 12.94 ± 1.49 μm
The oldest pooled AFT ages are found in the easternmost inliers of the Anti-Atlas, in East Saghro and Ougnat, which yield ages of 160.3 ± 6.5 and 156.0 ± 6.9 Ma, respectively, and MTL of 12.81 ± 1.15 and 12.45 ± 1.16 μm, respectively

Summary

Introduction

In Morocco, domains of outcropping Precambrian–Paleozoic basement along the Atlantic rifted margin (e.g., Meseta, Jebilet, Massif Ancient of Marrakech, and Anti-Atlas belt) were always recognized as relatively stable and not experiencing any major post-Variscan vertical movements (Michard 1976; Guiraud et al 1987, 2005). Km-scale crustal movements during the early post-rift time are documented elsewhere along the Atlantic Ocean: in the conjugate margin of Nova Scotia (Ravenhurst et al 1990; Grist and Zentilli 2003; Pe-Piper and MacKay 2006; Li et al 2012); the NE Brazilian margin (Harman et al 1998; Peulvast et al 2008; Bonow et al 2009; Jelinek et al 2014); and the W Greenland margin (Chalmers et al 1999; Japsen et al 2006; Bonow et al 2006). The new measurements are integrated with existing data sets to quantify the magnitude of subsidence and exhumation along the entire belt and their lateral extent to the east, away from the presentday shoreline of the Atlantic Ocean

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