Study of Monogenic Volcanism in a Karstic System: Case of the Maar of Lechmine n’Aït el Haj (Middle Atlas, Morocco)

Abstract

The Lechmine n’Aït el Haj maar (LNH) is a mixed phreatomagmatic-strombolian vent located in the Causse of the Middle Atlas. The application of tephrostratigraphic, and geophysical studies to the volcaniclastic deposits allowed interpreting the volcanic dynamics of this volcano set up during the Quaternary. Pyroclastic deposits allow us to understand the chronology of the eruptions. These are organized in four eruptive phases. The basal sequences are phreatomagmatic, followed by a strombolian unit. The last activity of LNH is phreatomagmatic. The structural analysis revealed a localized distension signed by fracture geometry, the mixed nature of the volcanism, tectonic markers, and the mechanisms of syn-eruptive tectonics. This subsidence, controlled by the NW-SE to WNW-ESE directions tends towards a strike-slip regime fault NE–SW during the phreatomagmatic-strombolian transition. The latter is favored by the position of the LNH volcano on the path of faults of cryptokarstic origin. The LNH maar is one of numerous well preserved monogenic volcanoes of the Causse of the Middle Atlas. The appropriation of this geoheritage is very important for tourism and territorial development of the region.