Accommodation of compression and lateral extension in a continental crust: Analogical modeling of the Central Atlas (eastern Algeria, Tunisia) and Pelagian sea

Abstract

At the eastern boundary of the North African Alpine Chain (NAAC), coexisting grabens, thrusts, and strike-slip faults form a complex structural pattern in the general context of Nubia-Eurasia plates convergence. In a context where the root of several major structures is poorly constrained, debates exist on the possible roles of orthogonal to shortening extension, décollement layer at the base of the Mesozoic cover, and lithospheric scale processes such as delamination. We present analog modeling experiments of shortening and/or orthogonal extension applied to an upper-crust consisting of sand lying on weighted silicon. When considered, a second silicon layer mimics a décollement at the basement-cover boundary.Our results highlight: 1) The regional structural pattern results from both crustal shortenings related to convergence between Nubia and Eurasia plates and orthogonal extensions due to a far-field pull of the Western-Hellenic/Dinaride subduction. 2) Several large-scale structures such as the Zaghouan thrust faults, the Sicilia Channel rift system, and the Gafsa Fault zone root deep into the continental crust. 3) The Atlas Triassic décollement layer is responsible for thin-skin tectonics in the Atlassic domain leading to the formation of surface folds called “Djebels”, extension in the “Fossés” area, and also favoring underplating of upper-crust slices in northern Tunisia. 4) Misfit on dominating extension direction at the wedge top between model and nature highlights the role of processes at the scale of the lithosphere such as the formation of a crustal root below the Atlassic wedge and opposite vertical motions between Atlas and Pelagian areas as a consequence of lithospheric delamination.