Petrogenesis of late Ediacaran volcanic rocks of the Kerdous and Tagragra d’Akka inliers (Anti-Atlas Morocco): Involvement of slab-failure

Abstract

Late Ediacaran rocks of the Ouarzazate Group define a thin pile of sediments and pyroclastic deposits between the Paleoproterozoic basement and the Cambrian sedimentary cover in the southern Kerdous and Tagragra d’Akka inliers. In the Tafeltast area, terrigenous sediments with volcano-sedimentary and pyroclastic rocks are located in grabens controlled by syn-sedimentary normal faults. The sedimentation is characterized by a maximum flooding outlined by the Agoujgal carbonates. In the Tagragra-n-Daouizid area, the Ouarzazate Group represents the surficial emission of rhyolitic pyroclastic flows. This pyroclastic activity was associated with continental coarse-grained sedimentary deposits. In the Tagragra Ouahallal area, the volcanic sequence is comparable to that observed in subglacial volcanoes. Massive ash layers, intrusive pillow lavas in waterlogged deposits, stacking of lava flows, alternation of emerged and submerged periods under shallow water, are characteristics described in sub-glacial mafic volcanoes.According to geochemical data, volcanic rocks of the Ouarzazate Group are: (i) mafic rocks with continental flood basalt and calc-alkaline basalt affinity; (ii) high-K calc-alkaline felsic rocks, generated by partial melting of crustal lithologies, or by an enriched mantle with involvement of crustal component; and (iii) intermediate to felsic slab failure rocks derived through mantle processes including melting of mafic upper portion of the subducted slab.