Magma mingling/mixing at Citlaltépetl volcano, eastern Trans-Mexican Volcanic Belt, and the plumbing system during the ∼5 ky BP Jamapa explosive eruption

The active Citlaltépetl volcano (Pico de Orizaba) located in the eastern part of the Trans-Mexican Volcanic Belt, is the highest mountain (5636 masl) in Mexico and North America. Intense explosive and effusive activity took place in the Holocene (mainly with VEI < 5), with some volcanic eruptions that have not yet been described, like the Jamapa Pyroclastic Flow deposit. Jamapa deposits were emplaced up to 4 km from the summit on the northern flank of the volcano, and rest on a paleosol dated at ~5 ky BP. The deposits consist of subrounded to rounded >30 cm-diameter porphyritic clasts of dacitic pumice (63.6 wt% SiO 2 ), andesitic scoria (58.9 wt% SiO 2 ), banded vesicular clasts (59.0 wt% SiO 2 ), andesitic dense volcanic bombs (62.8 wt% SiO 2 ), and magmatic crystalline enclaves (64.0 wt% SiO 2 ). The pumice contains plg + opx + cpx ± Fe-Ti oxides, and rare amph phenocrysts, whilst the scoria and banded clasts contain opx + cpx + amph + plag +/− Fe-Ti oxides. Glass matrix in all samples of the Jamapa Pyroclastic Flow a large compositional range is recorded (dacite to rhyolite; 66.6–78.2 wt% SiO 2 ), and plagioclase is also heterogeneous (An 23.3 to An 78 ), whereas pyroxene and amphibole are almost homogeneous in all samples. Cpx-liquid and amphibole geothermometry of the Jamapa juvenile components show significant differences among samples: andesitic scoria (900–946 °C), the pumice barren of amphibole (930 °C), and the banded sample (970–986 °C). On the other hand, the “MagMaTaB” liquid geothermobarometer model yielded 884 °C for the scoria, 934 °C for the banded, and 898 °C for the pumice samples. P-T results suggest the occurrence of at least two magmatic reservoirs beneath the volcano: a deep (~20 km), relatively mafic, and volatile-rich reservoir and a shallow (~8 km) reservoir with a felsic, stagnant magma. These results and the heterogeneous composition of the glass matrix and plagioclase crystals suggest that not only mingling but also mixing occurred during the Jamapa volcanic event. We conclude that a mafic magma stored at a depth of ~20 km ascended to reach the dacitic reservoir located ~8 km below the volcano, where both magmas were partially mixed, provoking overpressure of the system and eventually triggering the explosive eruption, destroying a pre-existing dome. • Citlaltépetl volcano recorded an explosive eruption some ~5 ka. • Mixing/mingling between andesitic and dacitic magmas triggered the eruption. • Dacitic magma stored at 8 km below the volcano with ~890 °C. • A deep reservoir occurs around ~20 km below Citlaltépetl volcano.