Textural heterogeneities in pumices from the climactic eruption of Mount Pinatubo, 15 June 1991, and implications for magma ascent dynamics
Textural heterogeneities in pumices from the climactic eruption of Mount Pinatubo, 15 June 1991, and implications for magma ascent dynamics
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1991 年 6 月 15 日皮纳图博山顶峰喷发的浮石的结构异质性及其对岩浆上升动力学的影响
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发表时间：
2001
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通讯作者：
M. Rosi
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作者：
M. Polacci;P. Papale;M. Rosi
皮纳图博火山的高潮事件代表了本世纪研究最彻底的火山爆发之一，并为爆炸性火山活动的动力学提供了重要的见解。我们对白色和灰色浮石进行了详细的结构分析，发现颜色和碎屑密度的差异反映了不同的晶体和囊泡数量和大小分布。白色浮石具有较高的囊泡性，囊泡变形，囊泡高度结合，壁薄，自面体现象晶体，无微晶。灰色浮石的囊泡性较低，囊泡数密度范围较宽，聚并有限，囊泡壁厚，变形少，斑晶和微斑晶有丰富的溶蚀，基质中普遍含有微晶和晶体碎片。白色和灰色浮石品种的存在，以及它们的泡泡数量和泡泡密度的广泛变化，似乎记录了岩浆泡泡和破碎等管道过程的复杂性，以及以不同流变行为为标志的管道区域的发育。特别是，本研究的结果表明，导管壁上强烈的剪切和粘性耗散可能很重要，这种机制可能是这次喷发中灰色浮石的形成和排放以及主要的白色浮石的原因。
The climactic event of Mount Pinatubo represents one of the most thoroughly studied eruptions of the century and has provided important insights into the dynamics of explosive volcanism. We have performed detailed textural analyses of the white and gray pumices of the plinian and pyroclastic flow deposits, and found that differences in color and clast density reflect different crystal and vesicle amounts and size distributions. White pumice has higher vesicularity, deformed and highly coalesced vesicles with thin walls, euhedral phenocrysts and microlite-free groundmass. Gray pumice shows lower vesicularity, wider ranges in vesicle number density, limited coalescence, vesicles with thick walls that are less deformed, phenocrysts and microphenocrysts with abundant solution pitting, and groundmass containing ubiquitous microlites and crystal fragments. The presence of white and gray pumice varieties and the broad range in vesicularity and vesicle number density that characterizes both of them appear to record the complexities of conduit processes such as magma vesiculation and fragmentation and the development of conduit regions marked by different rheological behaviors. In particular, the results of this study suggest the likely importance of intense shear and viscous dissipation at the conduit walls, a mechanism that may be responsible for the creation and discharge of the gray pumice of this eruption along with the dominant white variety.