The Sierra de Mil Cumbres, Michoacán, México: Transitional volcanism between the Sierra Madre Occidental and the Trans-Mexican Volcanic Belt

• We show the first geological map of the Sierra de Mil Cumbres, Michoacán, México.
• Atécuaro and La Escalera Calderas, Indaparapeo and Garnica Volcanic Complexes
• Basaltic‐andesite to dacitic calc‐alkaline lavas and rhyolitic ignimbrites
• Transition between the Trans-Mexican Volcanic Belt and the Sierra Madre Occidental

The Sierra de Mil Cumbres is a Miocene volcanic range located in central México, in the north-eastern part of the State of Michoacán, near the city of Morelia. Structurally it is a ENE-trending horst that covers an area of 1022 km2 (approximately 20 km wide × 60 km long) and contains exposures of chemically-bimodal volcanism in the form of ignimbrites, lava domes, lava flows, cinder cones, and related deposits. The main volcanic manifestations of this range are the La Escalera Caldera (16.3–23 Ma), the Garnica Volcanic Complex (18.3–17.9 Ma), the Atécuaro Caldera (16.3–19.4 Ma), and the Indaparapeo Volcanic Complex (14.1–17.5 Ma). The Sierra de Mil Cumbres stands in space and time at the intersection between the Miocene–Recent Trans-Mexican Volcanic Belt and the Late Cretaceous–Early Miocene Sierra Madre Occidental, and so provides new insights into the geological evolution of central México. Arc volcanism in the Sierra de Mil Cumbres was initiated by a massive NNW–SSE extension, probably during the counterclockwise rotation of the Sierra Madre Occidental. New geological mapping, stratigraphic analysis, detailed geochemistry and 40Ar/39Ar geochronology demonstrates that this intra-plate volcanism was emplaced between 14 and 23 Ma.