The southern Moroccan passive continental margin: An example of differentiated long-term landscape evolution in Gondwana

Abstract

The ENE-trending Anti-Atlas mountain belt reveals variation in recent topography with elevations of >3km indicating a differentiated long-term landscape evolution. To unravel the subsidence and exhumation history, low-temperature thermochronology has been applied on 21 samples from the Precambrian basement of the Irherm, Kerdous, Ifni, and Bas Drâa inlier. Thermochronological data suggest a common geological evolution of the western Anti-Atlas. Zircon fission-track ages from 287 (±23) to 331 (±24)Ma point to a main exhumation in the Late Carboniferous–Early Permian assigned to the Variscan folding and post-folding erosion. Zircon (U-Th)/He (205–287Ma) and apatite fission-track (120–219Ma) data are related to the Central Atlantic rift and drift stage, as the Anti-Atlas formed the exhumation shoulder of the rift system. The rock uplift and exhumation phase lasted up to the Early Cretaceous, whereby 9km of Precambrian–Palaeozoic overburden has been eroded. Thermal modelling reveals a minor sedimentary burial (1.5–2.5km) throughout the Cretaceous, in accordance with the widespread transgression across the northern Africa in the Cenomanian–Turonian. Apatite (U-Th-Sm)/He ages between 49 (±3) and 164 (±10)Ma confirm recent minor exhumation in the western Anti-Atlas with an increasing impact of the Atlasian orogeny and potentially a mantle plume anomaly from southwest to northeast reflecting the differentiated topography in the area.