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Abstract

The Quaternary Middle Atlas Volcanic Province is the largest and youngest volcanic field in Morocco. It hosts a hundred of well-preserved strombolian cones and maars which emitted numerous mafic pyroclastic deposits and lava flows covering a surface of ca. 960 km2 . The 2.27 Ma Aguelmane Sidi Ali monogenetic scoria cone was emplaced in a tectonic basin of the same name on the southern edge of the Bou-Anguer-Aïn-Nokra syncline in the eastern folded part of the Middle Atlas. Aguelmane Sidi Ali scoria cone was formed by a short-lived eruption of days to weeks. The eruptive dynamic recorded in the volcanic deposits suggested that the eruption started with an initial explosive activity that produced pyroclastic deposits of Strombolian type. Following this initial phase and as the cone grew, the eruption changed to a Hawaiian lava-fountain style. Volcanic activity emplaced agglutinate lava spatter near the vent in addition to lava flows with abundant inflation features such as tumuli and pressure-ridges. The continuous flow of significant lava volume provided significant pressure on the southern flank that breached the scoria cone. Subsequently, the eruption became more stable, and changed to a second regular Strombolian activity, rebuilding a new cone and leading to a volcano of 0.02 km3 . Aguelmane Sidi Ali history illustrates volcanological setting where tectonics and volcanism are intimately interrelated. Understanding this interaction is necessary for recognizing the relationship between tectonics, deformation processes and magma transport through the lithosphere.

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