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Dynamics of the ca. 4965 yr 14C BP "Ochre Pumice" Plinian eruption of Popocatépetl volcano, Mexico
The Ochre Pumice (OP) Plinian fallout was produced by Popocatépetl volcano in central Mexico, during a major Plinian eruption that occurred 4965±65 14C yr BP (3700 BC). The OP is part of the Ochre Pumice Sequence (OPS), that consists of surge, fall, and pyroclastic flow deposits. The OP Plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds. The juvenile component is mainly pumice (>83 wt.%), whereas the accidental components consist of igneous, sedimentary, and metamorphic clasts from the walls of the magma chamber and/or conduit. The vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase. This suggests increasing magma degassing prior and during the eruption. The chemical composition of the pumice varies insignificantly; at the base it is less evolved (SiO2 = 61 wt.%) and it becomes slightly more silicic towards the top (SiO2 = 63 wt.%). Pumice clasts have a crystallinity index that ranges between 10 and 25 vol.% and display a seriate texture with phenocrysts of euhedral plagioclase (PI) + clinopyroxene (Cpx)+orthopyroxene (Opx) + olivine (01) ± oxide (Ox) ± apatite (Ap). The size of the maximum lithic (2.5 cm) at a horizontal distance of 19 km indicates an eruption column height of 37-41 km. The isopach map allows the recognition of a dispersal axis that points towards the NNE, where an area of
ISSN : 0377-0273 CODEN : JVGRDQ
Journal of volcanology and geothermal research A. 2010, vol. 192, n° 3-4, pp. 212-231 [20 pages] [bibl. : 1 p.1/2]
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