The Hercynian tectonics in the Tassili-n-Ajjers area, Algeria: A possible continuous stress-strain regime?

Abstract

This work shed some light on the multiple tectonic phases occurred during the late Hercynian Orogeny that is related to the global plate tectonic geodynamics and their effects in the Tassili-n-Ajjers plateau area, which is located in the south-eastern edge of Saharan platform in Algeria, and known to be the southern margin of the Paleozoic Illizi Basin, wherewell preserved Paleozoic sedimentary rocks outcrop. Three Hercynian tectonic phases have been evidenced in the area are: Early Carboniferous (E1), Late Carboniferous-Permian (E2), and a Late Permian-Early Triassic (E3). The Hercynian tectonic regime in the Tassili-n-Ajjers area that was dominated by strike-slip movements during E1 and E2 tectonic phases changed into an extensional regime during E3 tectonic phase. Paleo-strain determination, folds axis distribution and the kinematic analyses of the strain field of the Hercynian active tectonic show a continuous deformation regime rather than discrete tectonic phases. Moreover, the progressive deformation regime is strongly supported by the absence of tectonic unconformities between Late Devonian/Early Carboniferous - Early Permian. At a large-scale, this continuous deformation appears as a result of a progressive closure of Rheic and western Paleotethys Oceans, and the clockwise rotation of African plate which occurred during the Hercynian/Variscan orogeny. Therefore, we could consider that the most part of Algerian Saharan platform has registered the far-field effects of this orogeny and provides a suitable illustration of an intracontinental deformation.