Dynamics of the ca. 4965 yr ¹⁴C BP “Ochre Pumice” Plinian eruption of Popocatépetl volcano, México

详细信息    查看全文

• 作者：Lilia Arana-Salinas ; Claus Siebe ; Jos&#xe9 ; Luis Mac&#xed ; as
• 关键词：Popocat&#xe9 ; petl ; Plinian eruption ; Ochre Pumice ; eruptive history ; radiocarbon dating
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2010
• 出版时间：10 May 2010
• 年：2010
• 卷：192
• 期：3-4
• 页码：212-231
• 全文大小：3362 K

文摘

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 (Pl) + clinopyroxene (Cpx) + orthopyroxene (Opx) + olivine (Ol) ± 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 ~ 300 km² was covered by >6 cm of pumice and ash. A minimum volume for the OP Plinian fallout deposit was calculated using a minimum thickness of 6 cm found at distal outcrops, and was estimated at ~ 4.9 km³ which corresponds to 2 km³ of dense rock equivalent (DRE). Stratigraphic relations indicate that the entire OPS was emplaced during a short time interval of a few days to weeks and consisted of three main different phases: phreato-magmatic, Plinian, and vulcanian. It started violently with the emplacement of surges and then culminated with the eruption of the OP fallout deposit. As the eruption advanced, discharge rates became more intermittent and the height of the column fluctuated and finally collapsed, generating pumice-and-ash flows that were emplaced around the volcano. This short but intense activity was followed during subsequent years by the growth of domes in the crater and the emplacement of block-and-ash-flows generated by vulcanian explosions.