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Post-Variscan exhumation of the Central Anti-Atlas (Morocco) constrained by zircon and apatite fission-track thermochronology

Authors


Correspondence: Professor Omar Saddiqi, Geology, Uni. Hassan II Casablanca, BP 5366 MAARIF, Casablanca 20000, Morocco. Tel.: +00212661413712; fax: +00212522230674; e-mail: omarsaddiqi@yahoo.fr

Abstract

The origin of the Anti-Atlas relief is one of the currently debated issues of Moroccan geology. To constrain the post-Variscan evolution of the Central Anti-Atlas, we collected nine samples from the Precambrian basement of the Bou Azzer-El Graara inlier for zircon and apatite fission-track thermochronology. Zircon ages cluster between 340 ± 20 and 306 ± 20 Ma, whereas apatite ages range from 171 ± 7 Ma to 133 ± 5 Ma. Zircon ages reflect the thermal effect of the Variscan orogeny (tectonic thickening of the ca. 7 km-thick Paleozoic series), likely enhanced by fluid advection. Apatite ages record a complex Mesozoic–Cenozoic exhumation history. Track length modelling yields evidence that, (i) the Precambrian basement was still buried at ca. 5 km depth by Permian times, (ii) the Central Anti-Atlas was subjected to (erosional) exhumation during the Triassic-Early Cretaceous, then buried beneath ca. 1.5 km-thick Cretaceous-Paleogene deposits, (iii) final exhumation took place during the Neogene, contemporaneously with that of the High Atlas.

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