Transition from polygenetic to monogenetic volcanism in southwestern Mexico City

Abstract The spatial and temporal transition from polygenetic to monogenetic volcanism was studied in a 15 km 2 area of southwestern Mexico City using Sentinel-1 SAR imagery (10 m), a 5 m LiDAR DEM, and geological mapping. Nineteen volcanic structures were identified: two dacitic polygenetic dome complexes (Ajusco and Los Picachos, ~ 3 Ma), ten intermediate-aged domes (1.6–0.18 Ma) and five younger monogenetic scoria cones, a fissure and a dike (~ 28–25.1 ka). Seven domes and one cone were previously unrecognized. New 40 Ar/ 39 Ar ages, from whole rock and groundmass, were obtained for the domes Ojo (1.624 ± 0.088 Ma), Cañada 1 (1.35 ± 0.12 Ma), and Cerro El Judío (1.328 ± 0.26 Ma), while relative ages of the other domes and scoria cones were estimated by stratigraphy and morphometry. Older polygenetic domes formed along N65°W-trending faults under compressional–transtensional stress, whereas younger scoria cones were emplaced within N65°W and E45°W-trending grabens under transtension. Intermediate domes extruded along N65°W grabens trending under lower stress. Geochemical analyses of 25 samples (domes, cones, flows) show that scoria cones cluster into distinct groups with higher Mg#, while domes exhibit lower Mg#. Although volumetrically similar to scoria cones, intermediate-aged domes share geochemical traits with polygenetic volcanoes, reflecting longer magma residence. The Lobos cone and the dike are geochemically similar to older volcanoes, whereas the Ojo and Roto domes align geochemically with scoria cones, suggesting deeper sources influenced by tectonic controls. Polygenetic volcanoes, intermediate domes, and scoria cones developed under different structural and magmatic regimes. Intermediate-aged domes mark the transition between long-lived polygenetic volcanism and short-lived monogenetic cones.