Phanerozoic Vertical Movements in Morocco

Our understanding of the Earth’s interior is limited by the access we have of its deep layers, while the knowledge we have of Earth’s evolution is restricted to harvested information from the present state of our planet. We therefore use proxies, physical and numerical models, and observations made on and from the surface of the Earth. The landscape results from a combination of processes operating at the surface and in the subsurface. Thus, if one knows how to read the landscape, one may unfold its geological evolution.In the past decade, numerous studies have documented km-scale upward and downward vertical movements in the continental rifted margins of the Atlantic Ocean and in their hinterlands. These movements, described as exhumation (upward) and subsidence (downward), have been labelled as “unpredicted” and/or “unexpected”. ‘Unpredicted’ because conceptual, physical, and numerical models that we dispose of for the evolution of continental margins do not generally account for these relatively recent observations. ‘Unexpected’ because the km-scale vertical movements occurred when our record of the geological history is insufficient to support them. As yet, the mechanisms responsible for the km-scale vertical movements remain enigmatic.One of the common techniques used by geoscientists to investigate the past kinematics of the continental crust is to couple ‘low-temperature thermochronology’ and ‘time-temperature modelling’. In Morocco alone, over twenty studies were conducted following this approach. The reason behind this abundance of studies and the related enthusiasm of researchers towards Moroccan geology is due to its puzzling landscapes and complex history. In this Thesis, we investigate unconstrained aspects of the km-scale vertical movements that occurred in Morocco and its surroundings (Canary Islands, Algeria, Mali, and Mauritania). The transition area between generally subsiding domains and mostly exhuming domains, yet poorly understood, is discussed via the evolution of a profile, running across the rifted continental margin (chapter 2). Low-temperature thermochronology data from the central Morocco coastal area document a km-scale exhumation between the Permian and the Early/Middle Jurassic. The related erosion fed sediments to the subsiding Mesozoic basin to the northwest. Basement rocks along the transect were subsequently buried between the Late Jurassic and the Early Cretaceous. From late Early/Late Cretaceous onwards, rocks present along the transect were exhumed to their present-day position.The post-Variscan thermal and geological history of the Anti-Atlas belt in central Morocco is constrained with a transect constructed along strike of the belt (chapter 3). The initial episode occurred in the Late Triassic and led to a km-scale exhumation of crustal rocks by the end of the Middle Jurassic. The following phase was characterised by 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 a km-scale exhumation throughout the Late Cretaceous and the Cenozoic. The exhumation episodes extended into the interior of the African tectonic plate, perhaps beyond the sampled belt itself. Exhumation rates and fluxes of material eroded from the hinterlands of the Moroccan rifted margin were quantified from the Permian (chapter 4). The high denudation rates, obtained in central Morocco during the Early to Middle Jurassic and in northern Morocco during the Neogene, are comparable to values typical of rift flank, domal, or structural uplifts. These are obtained in central Morocco during the Early to Middle Jurassic and in northern Morocco during the Neogene. Exhumation rates for other periods in northern to southern Morocco average around ‘normal’ denudation values. Periods of high production of sediments in the investigated source areas are the Permian, the Jurassic, the Early Cretaceous, and the NeogeneThe Phanerozoic evolution of source-to-sink systems in Morocco and surroundings is illustrated in several maps (chapter 5). Substantial shifts in the source areas were evidenced between the central and northern Moroccan domains during the Middle-Late Jurassic and between the Meseta and the Anti-Atlas during the Early-Late Cretaceous. Finally, the mechanisms responsible for the onset and subsistence of the unpredicted km-scale vertical movements are discussed (chapter 6). We propose that a combination of the large-scale crustal folding, mantle-driven dynamic topography, and thermal subsidence, superimposed to changes in climates, sea level and erodibility of the exposed rocks, were crucial to the timing, amplitude, and style of the observed vertical movements.The km-scale vertical movements will continue to be studied for years to come. Expectantly, this Thesis will deliver sufficiently robust grounds for further elaborated and integrated studies in Morocco and beyond.