Role of conduit shear on ascent of the crystal-rich magma feeding the 800-year-b.p. Plinian eruption of Quilotoa Volcano (Ecuador)
Role of conduit shear on ascent of the crystal-rich magma feeding the 800-year-b.p. Plinian eruption of Quilotoa Volcano (Ecuador)
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导管剪切对富含晶体的岩浆上升的作用，为 800 年历史提供了水源。
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
D. Zandomeneghi
中科院分区：
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作者：
Mauro Rosi;Patrizia Landi;M. Polacci;A. D. Muro;D. Zandomeneghi
我们的特点浮石产品属于800年b. p.基洛托阿喷发的高潮阶段。散装岩石成分，岩相学，矿物和玻璃化学和质地的调查进行了三个端员浮石类型，即白色，灰色，混合浮石。所有研究的浮石碎屑都是英安岩，其特征在于相同的岩石成分和矿物组合，但玻璃成分和整体结构根据不同的浮石类型而变化。白色浮石具有较高的结晶度（~48重量%），丰富的自形表型/微斑晶，无基质微晶，最进化的玻璃成分（74-78重量% SiO2），以及以变形和高度聚结的薄壁囊泡为特征的异质囊泡群体。灰色浮石具有较低的结晶度（29-36重量%），丰富的破碎和/或再吸收的晶体，无处不在的基质斑晶碎片和微晶，最广泛的玻璃组合物（69-78重量% SiO2），和相当均匀的变形差和合并的囊泡与较厚的壁。混合浮岩的特征是具有白色和灰色浮岩成分和结构特征的条带或斑块交替出现。我们属性的玻璃成分和晶体和囊泡纹理的不均匀性发生在火山管道的岩浆上升到表面的过程。特别是，上述观察和结果是一致的灰色岩浆的起源加热的原始白色岩浆在强烈剪切区域的管道，因为在管道壁的粘性耗散和晶体研磨和再吸收的机制。因此，粘性较低的灰色岩浆将使喷发的高质量通量的发生和保存成为可能，否则很难解释高粘性富含晶体的英安质岩浆。
We have characterized pumice products belonging to the climactic phase of the 800-year-b.p. Quilotoa eruption. Bulk rock compositions, petrography, mineral, and glass chemistry and textural investigations were performed on the three end-member pumice types, namely white, gray, and mingled pumices. All the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage, but glass compositions and bulk textures change according to different pumice types. White pumice has higher crystallinity (~48 wt%), abundant euhedral pheno/microphenocrysts, no groundmass microlites, the most evolved glass compositions (74–78 wt% SiO2), and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls. Gray pumice exhibits lower crystallinity (29–36 wt%), abundant broken and/or resorbed crystals, ubiquitous groundmass phenocryst fragments and microlites, the widest range of glass compositions (69–78 wt% SiO2), and quite homogeneous poorly deformed and coalesced vesicles with thicker walls. Mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics. We attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface. In particular, the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls. The less viscous gray magma, therefore, would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal-rich dacitic magmas.