干旱区生态环境知识资源中心

The Upper Paleozoic geodynamic evolution is discussed at the scale of a wide part of Gondwana from North Africa to Arabia. With the aim of giving an integrated tectonic scenario for the study domain, we revisit six key areas, namely, the Anti-Atlas Belt (Morocco), the Bechar Basin (west Algeria), the Hassi R’Mel High (central Algeria), the Talemezane Arch (south Tunisia), the Western Desert (Egypt), and, finally, the High Zagros Belt (Iran). Below the so-called Hercynian unconformity, which is in reality a highly composite discontinuity, surface and subsurface data display a well-known arch-and-basin geometry, with basement highs and intervening Paleozoic basins. We show that this major feature results mainly from a Late Devonian event and can no longer be interpreted as a far effect of the Variscan Orogeny. This event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence, in the western part of the system, or by an important uplift of probable thermal origin followed by erosion and peneplanation. By the end of the Devonian, the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere. Such a primary configuration is preserved in Arabia with typical sag geometry of the Carboniferous and Permian deposits but strongly disturbed elsewhere by the conjugated effects of the Variscan Orogeny during the Carboniferous and/or by subsequent uplifts linked to the central Atlantic and Neo-Tethys rifting episodes. In conclusion, we try to integrate this new understanding in the geodynamics of the Late Devonian, which at world scale is characterized by the onset of the Variscan Orogeny on the one hand and by magmatism, rifting, and basement uplift on the other hand.