Subsurface interconnection beneath the Mio-Plio-Quaternary volcanoes of the Ain Leuh causse (Middle Atlas, Morocco): Structural framework and emplacement mechanisms

Abstract

In the Ain Leuh causse, located southwest of the Middle Atlas Volcanic Province (MAVP), a combined study using aeromagnetic data, fieldwork, and remote sensing is carried out to improve our understanding of the subsurface structure and its correlation with surface structural and volcanic features. The tectonically controlled emplacement mechanisms of the MAVP, which continue to hold undisclosed aspects, were investigated as well. Numerous techniques and mathematical filters for edge detection and 2D modelling were used. The main observations show that the positive magnetic anomalies in the study area are mainly related to the magmatic activity, which was organized into two main episodes: i) Triassic, with a tholeiitic affinity, well recorded along the NE-SW inherited Variscan faults; and ii) Mio-Plio-Quaternary, with an alkaline affinity, forming scoria cones, maars, and lava flows. They are also expressed as hidden domes, laccoliths, and interconnected magma bodies revealed by 2D modelling of the aeromagnetic data. Uncommon coarse-grained undersaturated alkaline rocks crop out in Talzast dome (Talzastite, Fasinites, and Ankaratrite). They are unique in the MAVP and restricted to this part of the Middle Atlas. 2D aeromagnetic modelling has revealed the presence of shallow magmatic rocks bodies beneath Talzast dome. The extracted structural lineaments using aeromagnetic data and remote sensing reveal that the structural framework of the study area is controlled by NE-trending faults reaching depths of up to 3000 m, which is the depth of the magnetic signature of the faults. Additionally, NNE, NNW and N-trending short-length lineaments are defined and rooted at depths up to 3000 m. The predominant NE-SW structural trend may be linked to the reactivation of Hercynian faults during Alpine tectonics. These faults likely controlled the emplacement of the Mio-Plio-Quaternary volcanism in the area. The magma reservoirs that would have fed the various volcanic edifices are located at a shallow depth of less than 500–2000 m.