Abstract

The El Jadida – Agadir basin shows an evolution related to that of the central Atlantic rifting history. The synrift period (late Early Triassic to earliest Jurassic) is dominated by deposition of red clastic sediments and evaporites, which are overlain by or intercalated with basalt flows. Two intense extensional phases are recognized. The first, probably in Middle Triassic times, is oriented north-northwest–south-southeast and resulted in the formation of east-northeast–west-southwest-oriented grabens and half-grabens. The second, a widespread northwest–southeast-trending extension, is Ladinian to earliest Liassic, and induced the formation of westward-dipping half-grabens. Extensional tectonics initiated in the southern part of the basin and migrated northwards, contrary to classical ideas proposing rifting from north to south. The postrift evolution is characterized by Jurassic to Eocene subsidence. Tectonism appears to have been restricted to a narrow area close to the present-day coast. Subsidence history shows four stages of rapid subsidence disrupting the thermal-relaxation period. The values of extension are moderate, ranging from 1.1 to 1.34. The best model that accounts for this evolution is the one combining simple shear at the onset of rifting and pure shear by its end.

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