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

摘要

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.