Reconstructing the middle to late Pleistocene explosive eruption histories of Popocatépetl, Iztaccíhuatl and Tláloc-Telapón volcanoes in Central México

Abstract The Sierra Nevada Volcanic Range (SNVR), which includes Popocatepetl, Iztaccihuatl and Tlaloc-Telapon volcanoes, has been the source of multiple large explosive eruptions that have dispersed tephra across central Mexico. Several eruptions since 40 ka have previously been described, particularly from Popocatepetl, the southernmost volcano of the range. However, the longer-term eruption history of the SNVR is poorly understood, due to challenges with correlating limited exposures of older pyroclastic sequences, and in discriminating between tephras derived from different sources. Here we describe two extensive exposures located between Popocatepetl and Iztaccihuatl volcanoes, which provide a more complete and longer-term explosive eruption record of the SNVR: the Nepopualco and Xalitzintla tephra sequences. A detailed tephrostratigraphic survey, together with new 40Ar/39Ar geochronological analyses and glass geochemistry, has permitted the characterization of identified eruption units further leading to the determination of geochemical fields for each volcano and the subsequent discernment of volcanic sources. Our results show that, since the collapse of Los Pies Cone, which destroyed the Paleo-Iztaccihuatl edifice at 631 ± 44 ka (2σ), Iztaccihuatl has produced at least 6 explosive rhyolitic eruptions. After coeval activity with Popocatepetl, between ~600 and ~ 500 ka, Iztaccihuatl's explosive activity ceased while Popocatepetl's continued until present day. Popocatepetl has produced at least 27 medium to large explosive eruptions (inferred VEI 4–6), commonly of andesitic to dacitic compositions. Some of these eruptions deposited pumice fallout of >1 m thick in both the Nepopualco and Xalitzintla sequences (e.g. the 339 ± 16 ka [2σ] NT-23/WRT-7 eruption), suggesting that Popocatepetl has produced several eruptions similar in magnitude to well-known the ~14 ka Tutti Frutti Pumice (a VEI 6 eruption with a ~ 5 km3 tephra volume). The Popocatepetl and Iztaccihuatl tephras are interbedded with deposits from more distal volcanoes, including some mafic to intermediate products of unknown sources (possibly from nearby monogenetic cones) and tephras related to the late Pleistocene eruptions of Tlaloc-Telapon (including the tephra layer produced by the San Valentin Ignimbrite, recently 40Ar/39Ar dated in this study at ~102 ka; 2σ). Our new chemical, stratigraphic and geochronologic investigations of these pyroclastic deposits, predominantly from Popocatepetl and Iztaccihuatl, provide information on the scale and frequency of medium to large magnitude explosive eruptions over a longer-time period than currently known and that have had potential to disperse tephra across central Mexico since the middle to late Pleistocene. This new data can be used to determine the source of further unknown tephras in the region as well as to better assess the volcanic hazard to the densely populated megalopolis of Mexico City.