Abstract
<p>Recent studies have shown that the uplift of the Moroccan Atlas Mountains resulted from a combination of crustal shortening and mantle thermal processes in the interior of the African plate. Within this framework, to gain insight into the dynamics of these processes in recent times, we investigated the nature and rates of the Quaternary deformation in a case field area, namely, the northern Ouarzazate Basin, which contains the best dated records of fan and fluvial terrace deposits of the Atlas system. The area selected is in the southern orogenic front of the High Atlas, where thrusts and fault-related folds have affected a sequence of dated, stepped terraces to varying degrees. Based on cosmogenic nuclide surface exposure dating, we have calculated slow neotectonic deformation rates for the past ~250 ky. We have measured the local rates of structural uplift, yielding 0.2 mm/y in areas of the northern third of the Ouarzazate Basin. We have estimated slip rates at 0.09-0.15 mm/y for the most active fault within the basin. We also document that recent shortening rates (~0.1 mm/y during the last ~250 ky) almost double the average rates from the deformation onset (~0.04 mm/y since the Middle Miocene). These results raise the point of the possible relations between such increases in the deformation rates and the erosional denudation of the Ouarzazate Basin since it became externally drained in the late Pliocene or early Quaternary times.</p>
Highlights
Over the past 10 years, different studies have investigated the relationships between crustal shortening, mantle uplift, and surface processes, as the factors that control the topography of the Atlas Mountain system in Morocco [Teixell et al 2003, Arboleya et al 2004, Teixell et al 2005, Missenard et al 2006, Babault et al 2008]
Most of the orogenic shortening in the High Atlas is concentrated in the southern frontal thrust belt, which affects Cretaceous to Neogene rock and overrides the Ouarzazate foreland basin [Laville et al 1977, Fraissinet et al 1988, Görler et al 1988, Errarhaoui 1997]
Morphotectonic analysis and structural uplift We focused our structural analysis on the frontal-most thrust faults of the South Atlas Front (SAF) in the north-western Ouarzazate Basin (Figure 2)
Summary
Over the past 10 years, different studies have investigated the relationships between crustal shortening, mantle uplift, and surface processes, as the factors that control the topography of the Atlas Mountain system in Morocco [Teixell et al 2003, Arboleya et al 2004, Teixell et al 2005, Missenard et al 2006, Babault et al 2008]. The semi-arid climate of the southern High Atlas and the erosive dynamics of the Ouarzazate Basin allowed the development and preservation of extensive Quaternary terrace deposits, which cover much of the current surface of the basin As these represent potentially datable surfaces, the Quaternary deposits that cross active faults and folds make ideal strain markers for the study of rates and kinematics of recent deformation [e.g., Avouac et al 1993, Lavé and Avouac 2000, Thompson et al 2002, Gold et al 2006, Amos et al 2007]. Most of the orogenic shortening in the High Atlas is concentrated in the southern frontal thrust belt (the SAF), which affects Cretaceous to Neogene rock and overrides the Ouarzazate foreland basin [Laville et al 1977, Fraissinet et al 1988, Görler et al 1988, Errarhaoui 1997]. A system of stepped alluvial fans and fluvial terraces formed during the late Pleistocene and Holocene, punctuating the incision
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