The Nieve volcanic cluster: A Pliocene - Pleistocene lava dome cluster in the Michoacán-Guanajuato volcanic field (México)

Abstract

The Nieve monogenetic volcanic cluster is located in the central–eastern region of the Michoacán–Guanajuato volcanic field, along the Huiramba fault zone, a relay ramp in the Morelia–Acambay fault system produced by oblique north-northwest transtension. This volcanic cluster includes at least 17 middle Pliocene to late Pleistocene lava domes, two small shield volcanoes, and two scoria cones. Between 4 and 3.8 Ma, two effusive eruptions built two small shield volcanoes overlying one another, with a magma volume of 3.93 km³. Between 2.9 Ma and 21.4 ka, 17 lava domes and two scoria cones were emplaced on the flanks of these volcanoes. The entire cluster resulted in a total erupted volume of 17 km³, covering an area of  326 km² and reaching a thickness of emplaced volcanic material of 1200 m, resulting in a magma eruption rate equivalent to 0.004 km³/ka. All the rocks associated with this cluster are within a relatively restricted range in composition, between 53.9 and 64.2 wt% SiO₂, from andesite enriched in silica to basaltic andesite. The presence of intrusive-rock xenoliths and xenocrysts with dissolution textures reveals that assimilation processes modified the magmas. Based on the regional geological record, we suggest that the establishment of the Nieve volcanic cluster has been controlled by tectonic structures and the basement of the region, which has allowed the chemical evolution of these magma batches that probably had sources in at least two deep reservoirs as reflected by the Nb/Th versus Ta/U ratio.