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TECTONICS, VOL. 18, NO. 2, PAGES 163–184, 1999

Inversion tectonics and the evolution of the High Atlas Mountains, Morocco, based on a geological-geophysical transect

Weldon Beauchamp

Institute for the Study of the Continents, Cornell University, Ithaca, New York


Richard W. Allmendinger

Institute for the Study of the Continents, Cornell University, Ithaca, New York


Muawia Barazangi

Institute for the Study of the Continents, Cornell University, Ithaca, New York


Ahmed Demnati

Office National de Recherches et d'Exploitations Pétrolères, Rabat, Morocco


Mohamed El Alji

Office National de Recherches et d'Exploitations Pétrolères, Rabat, Morocco


Mohammed Dahmani

Division de la Géologie Générale, Ministère de l'Energie et des Mines, Rabat, Morocco


Abstract

The High Atlas Mountains of North Africa were formed over a major intracontinental rift system that had extended from what is now the Atlantic margin of Morocco to the Mediterranean coast of Tunisia. The Atlas rift system began in the Triassic and was active through the Jurassic. The inversion phase of the Atlas rift system began in the Early Cretaceous and extended into the present. The major uplift phase occurred between 30 and 20 Ma (Oligocene-Miocene) and corresponds to the Alpine orogenic event. The uplift and inversion of the Atlas rift system resulted in a shortening of the rift basin by a minimum of 36 km. A restoration of the deformed cross section indicates the original Atlas rift basin was approximately 113 km wide, comparable to the width of the present-day Red Sea. Synrift and postrift sedimentary rocks were uplifted by the reactivation of synrift normal faults, with further shortening along newly formed thin-skinned thrust faults. Structures formed by the reactivation of synrift faults resulted in structures with different geometries than those created by newly formed fault-bend and fault-propagation faults. Shortening across the High Atlas Mountains involved a partitioning of strain, with the greatest magnitude of shortening occurring along the margins of the High Atlas Mountains.

Received 13 March 1998; accepted 9 October 1998.

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Citation: Beauchamp, W., R. W. Allmendinger, M. Barazangi, A. Demnati, M. El Alji, and M. Dahmani (1999), Inversion tectonics and the evolution of the High Atlas Mountains, Morocco, based on a geological-geophysical transect, Tectonics, 18(2), 163–184.