Reconstruction of the eruptive processes and new 40Ar/39Ar dating of Plio-Pleistocene monogenetic volcanism in the Folded Middle Atlas (Northern Morocco). Implications of eruption style variation with climate changes

During the Plio-Pleistocene, several individual monogenetic volcanoes were emplaced in the Folded Middle Atlas region in Central Morocco. These eruptions are primarily concentrated on anticlinal ridges and are structured by a network of NNE-SSW-oriented faults, inherited from Alpine or older tectonic phases. This study investigates three Pleistocene (2.5-0.8 Ma) small scoria cones and one partially preserved maar, here dated with 40Ar/39Ar geochronology to 0.281 Ma, indicating the youngest hydrovolcanic eruption of this area. The temporal distribution and morphological diversity of volcanic edifices in northern Africa during the Plio-Pleistocene are inferred to be closely associated with paleoclimatic fluctuations, which alternated between arid and humid phases. Strombolian explosive eruptions created scoria cones primarily during arid periods, facilitating magmatic outgassing with minimal interaction between magma and the water table. In contrast, hydro-volcanic eruptions were promoted by wetter climatic conditions, which were susceptible to interaction between upwelling magma and surface water or shallow aquifers. Scoria cones consist of pyroclastic deposits of varying grain sizes, including scoriaceous pyroclasts such as small portions of coarse ash lapilli and volcanic bombs with different morphologies. Their last eruptive activity phases are typically represented by thin lava flows, indicating a gradual shift to Hawaiian-type mild explosive dynamics. Conversely, maar formations are characterized by ejecta deposits from phreatomagmatic explosions, indicating rapid interaction between magma and varying volumes of external water, likely occurring during a single eruptive event.