Reconstructing the Pre-Alpine cycle of Moroccan Atlas system before the inversion phase

Abstract

The Wilson Cycle (ca. 250-300 Ma) is driven by plate tectonics, and is expressed by the opening of oceanic basins, which are subsequently closed to form orogens. Morocco has experienced several orogenic cycles: e.g., Eburnean, Pan-African, Hercynian (Variscan) and Alpine (Atlasian). The last Wilson Cycle that shaped the geology of Morocco is the Alpine Cycle (300-0 Ma). It started by the dismantlement of the Pangea Supercontinent leading to the opening of the Atlantic Ocean and the Atlas rift system. The latter was subsequently aborted and inverted into a fold-and-thrust belt during the Cenozoic, due to the opening of the South Atlantic and the convergence between Africa and Iberia-Europe. The Atlas system of NW Africa includes two intracontinental ranges, the High and Middle Atlas extending ENE-WSW and NE-SW, respectively. It is a key piece in the Pangea breakup puzzle, as its evolution captures the kinematic of the African plate during Mesozoic to Cenozoic times. Several studies have examined the structural and stratigraphic architectures of the Atlas system during the rifting phase, by removing the Alpine inversion along palinspaticly reconstructed 2D sections. However, little was done to investigate the crustal structure and the amount of crustal stretching during the Triassic to Jurassic extension. This work aims to reconstruct the pre-alpine architecture of the Atlas system and link it directly with the evolution of the crust. Our goal is to provide insights into the amount of crustal thinning that took place during the Mesozoic rifting in the Atlas domain and constrain the strain distribution within the African plate during the dismantlement of the Pangea.Key words: Wilson cycle; Atlas system; Pangea; Break up; Inversion; Pre-Alpine cycle.