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New Insights in the Geodynamic Evolution of the Atlantic Margin Offshore Essaouira (Morocco)

Abstract

This study is based on recently acquired 2D seismic reflection data of the 2011 MIRROR experiment and provides new insights into the crustal architecture and the syn-rift and post-rift geodynamic evolution of the Atlantic margin offshore Morocco. It focuses on seismic-based structural analysis and gravity modeling and suggests mantle denudation along a major crust-mantle detachment during the Early to Middle Jurassic. The data further indicate that mid-oceanic ridge seafloor spreading might have only started in Middle to Late Jurassic times. The prominent Base Tertiary Unconformity (BTU) is related to a regional hiatus. We observed salt canopies in levels at and above the unconformity, and their emplacement by salt extrusion on the seafloor is interpreted to be contemporaneous to the hiatus event. The BTU is interpreted to have formed earlier in the northern study area (approx. Cenomanian age at DSDP 416) and propagated through time to the south (approx. Coniacian age at DSDP 415). We postulate that this diachrony influenced regional differences in salt preservation: today, salt diapirs dominate the Agadir Basin in the south of the study area, and the Ras Tafelnay Plateau is characterized by massive salt canopies; in contrast, in the north, where the hiatus lasted longer (offshore Essaouira and Safi Basins), weld structures and associated deformation suggest an important loss of salt in the past, resulting in the preservation of salt-poor canopy remnants. Furthermore, our interpretation indicates a tectonic reactivation of pre-existing oceanic and syn-rift basement faults during the Early Paleogene. This structural event was accompanied by volcanism and also formed a series of deep water anticlines with associated deformation in the overlying sediments. This study proposes a diachronic southward trend for the basement fault reactivation, similar to BTU. In conclusion, we postulate a tempo-spatial relation between the relative north-south motion of the Canary Island hotspot, the diachrony of the BTU and the reactivation of basement faults. The major hiatus might indicate a regional Late Cretaceous uplift related to the approaching hotspot, followed by a more local uplift above the hotspot center during the Early Paleogene. The reactivation of basement faults associated with the emplacement of volcanic intrusions is interpreted to result from this latter local uplift.