New Evidence of ‘Anomalous’ Vertical Movements along the Hinterland of the Atlantic NW African Margin

Abstract

Low-temperature thermochronology studies revealed major exhumation events affecting domains in the hinterland of the Central Atlantic margins, where Palaeozoic and/or Precambrian basement is exposed. Thus, domains traditionally assumed to be stable since at least the Variscan and juxtaposed to subsiding Meso-Cenozoic basins, appear to be affected by km-scale vertical movements during the Atlantic rifting and after the Early Jurassic breakup in the Central Atlantic. In this contribution, we investigate the extent and the magnitude of these motions along the NW African margin by presenting the first low-temperature thermochronology data from west Mauritania. The analysed 22 samples were collected along the Mauritanides, a N-S trending Variscan Belt separating the cratonic Taoudeni Basin in the east from the Atlantic coastal basin in the west. The obtained apatite fission track (AFT) ages range between 236 and 90 Ma, with mean track lengths between 11.22 and 12.81 μm and D_par comprised between 1.6 and 2.1 μm. The uncorrected (U-Th-Sm)/He (AHe) ages vary between 261 and 33 Ma. Inverse thermal modelling of the AFT and AHe data indicates that the hinterland of the Mauritanian Atlantic margin experienced (i) burial between the Permian and the Late Triassic, (ii) km-scale exhumation during Middle-Late Jurassic and Early Cretaceous, (iii) burial during the Palaeogene–early Miocene, and (iv) exhumation between mid-Miocene and present-day. We argue that these vertical movements are primarily driven by the tectonic evolution of the Atlantic rift and the subsequent geodynamic evolution of the Central Atlantic Ocean and the African plate.