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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Dynamics of the ca. 4965 yr ~(14)C BP 'Ochre Pumice' Plinian eruption of Popocatepetl volcano, Mexico
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Dynamics of the ca. 4965 yr ~(14)C BP 'Ochre Pumice' Plinian eruption of Popocatepetl volcano, Mexico

机译：动力学的ca。 4965年〜（14）C BP波帕卡特佩特尔火山的'Ochre Pumice'Plinian喷发

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摘要

The Ochre Pumice (OP) Plinian fallout was produced by Popocatepetl volcano in central Mexico, during a major Plinian eruption that occurred 4965±65 ~(14)C 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 (SiO_2 = 61 wt.%) and it becomes slightly more silicic towards the top (SiO_2 = 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 (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 km~2 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 km~3 which corresponds to 2 km~3 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.
机译：Mexico石浮石（OP）的Plinian沉降物是墨西哥中部的Popocatepetl火山在一次重大Plinian喷发期间产生的，该喷发发生于4965±65〜（14）C yr BP（3700 BC）。 OP是O石浮石序列（OPS）的一部分，由潮涌，跌落和火山碎屑流沉积物组成。 OP Plinian沉降物显示出双峰粒度分布，分选程度不佳至中度，向上层逐渐提高。幼年成分主要是浮石（> 83 wt。％），而偶然成分则包括来自岩浆室和/或导管壁的火成岩，沉积岩和变质岩屑。浮石的囊泡性从地层序列的底部到顶部降低，而晶体和玻璃含量增加。这表明在喷发之前和喷发期间岩浆脱气增加。浮石的化学成分变化不大。在基部，它的析出较少（SiO_2 = 61 wt。％），而向顶部的硅含量稍高（SiO_2 = 63 wt。％）。浮石碎屑的结晶度指数在10％至25％（体积）之间，并呈现出具有锯齿质感的表皮纹理，其表面为正斜方晶（PI）+斜ino（Cpx）+邻苯二酚（Opx）+橄榄石（Ol）±氧化物（Ox）±磷灰石（Ap）。水平距离为19 km时最大岩屑（2.5 cm）的大小表示喷发柱高度为37-41 km。等值线图允许识别指向NNE的分散轴，该区域的〜300 km〜2区域被> 6 cm的浮石和灰烬覆盖。利用在末梢露头处发现的最小厚度6 cm计算出OP Plinian沉降物的最小体积，估计为〜4.9 km〜3，相当于2 km〜3的致密岩石当量（DRE）。地层关系表明，整个OPS发生在几天到几周的短时间间隔内，由三个主要的不同阶段组成：岩浆岩浆期，普利尼期期和伏尔加期期。它开始于激增的猛烈爆发，然后随着OP余尘沉积的爆发而达到高潮。随着喷发的进行，排放速率变得更加断断续续，塔的高度开始波动并最终崩溃，从而产生了浮在火山周围的浮灰流。在随后的几年中，这种短暂而激烈的活动随后是火山口圆顶的增长以及由火山爆发产生的块状和灰烬流的进入。

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