The Plinian phase of the Campanian Ignimbrite eruption (Phlegrean Fields, Italy): evidence from density measurements and textural characterization of pumice
The Plinian phase of the Campanian Ignimbrite eruption (Phlegrean Fields, Italy): evidence from density measurements and textural characterization of pumice
复制标题
坎帕尼亚熔岩喷发的普林尼阶段（意大利Phlegrean Fields）：来自浮石密度测量和结构特征的证据
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
M. Rosi
中科院分区：
文献类型：
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作者：
M. Polacci;L. Pioli;M. Rosi
从爆炸性火山爆发的浮石碎屑的纹理特征提供了限制岩浆过程通过量化晶体和囊泡的内容，大小，形状，囊泡壁厚和互连程度。普林尼沉降存款直接下坎帕尼亚火山灰（CI）喷发是一个合适的情况下，调查浮石产品具有不同的纹理特征，并将调查结果的过程伴随导管岩浆上升到火山口。该存款由下部（LFU）和上部（UFU）浮石火山碎屑层组成，由<5体积%的粗面质岩浆亚稳定喷发产生。晶体和峰值放电率为3.2×108 kg/s。对从Voscone型露头的不同地层间隔采集的样品进行了密度测量，并通过图像分析技术在不同放大倍数下对其纹理特征进行了研究。根据碎屑的密度、形态和泡囊结构，将浮石碎屑分为微泡（不均匀泡囊）、管状（伸长/变形泡囊）和膨胀型（合并/膨胀泡囊），结合密度数据和泡囊结构研究，对浮石碎屑的代表区域和泡囊结构进行了表征。体积囊泡的范围很宽，从0.46到>0.90不等，囊泡的数量密度在107-108 cm−3之间。所有浮石类型的囊泡聚结的程度都很高，相互连接的囊泡通常占散装囊泡人口的90%以上。结果表明，从两个阶段的喷发和在每个喷发阶段，不同的浮石类型，也在每个单一的浮石类型的碎片之间的浮石碎屑高度的异质结构。具有不同结构特征的浮石碎屑的成因归因于以不同流变行为为标志的导管区的发育。本研究的结论是，囊泡变形，聚结的程度和强烈的剪切管道壁的脱气过程中发挥了重要作用，从而影响整个管道动力学。
Textural characterization of pumice clasts from explosive volcanic eruptions provides constraints on magmatic processes through the quantification of crystal and vesicle content, size, shape, vesicle wall thickness and the degree of interconnectivity. The Plinian fallout deposit directly underlying the Campanian Ignimbrite (CI) eruption represents a suitable case to investigate pumice products with different textural characteristics and to link the findings to processes accompanying conduit magma ascent to the crater. The deposit consists of a lower (LFU) and upper (UFU) pumice lapilli bed generated by the sub-steady eruption of trachytic magma with <5 vol%. crystals and a peak discharge rate of 3.2×108 kg/s. Density measurements were performed on samples collected from different stratigraphic intervals at the Voscone-type outcrop, and their textural characteristics were investigated at different magnifications through image analysis techniques. According to clast densities, morphologies and vesicle textures pumice clasts were classified into microvesicular (heterogeneous vesicles), tube (elongated/deformed vesicles) and expanded (coalesced/inflated vesicles).The combination of density data and textural investigations allowed us to characterize both representative areas and textural extremes of pumice products. Bulk vesicularity spans a broad interval varying from 0.46 to >0.90, with vesicle number density ranging from 107–108 cm−3. The degree of vesicle coalescence is high for all pumice types, with interconnected vesicles generally representing more than 90% of the bulk vesicle population. The results show a high degree of heterogeneous textures among pumice clasts from both phases of the eruption and within each eruption phase, the different pumice types and also within each single pumice type fragment. The origin of pumice clasts with different textural characteristics is ascribed to the development of conduit regions marked by different rheological behavior. The conclusions of this study are that vesicle deformation, degree of coalescence and intense shear at the conduit walls play a major role on the degassing process, hence affecting the entire conduit dynamics.