Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering: Chapter 30 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006
Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering: Chapter 30 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006
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2004-2006 年圣海伦斯火山熔岩穹顶的岩石学——对岩浆管道和喷发触发的影响：《火山重新点燃：圣海伦斯火山再次喷发，2004-2006 年》第 30 章
DOI：
10.3133/pp175030
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发表时间：
2008
影响因子：
10.5
通讯作者：
G. Meeker
中科院分区：
文献类型：
--
作者：
J. Pallister;C. Thornber;K. Cashman;M. Clynne;H. Lowers;C. Mandeville;I. Brownfield;G. Meeker
1986年，形成圆顶的火山喷发结束，18年后，在没有任何预警的情况下，圣海伦火山于2004年10月再次喷发。在随后的两年里，火山喷出了超过80×10 6立方米的含气少、富含晶体的英安岩熔岩。2004年至2004年的英安岩在大块岩石组成上非常一致，sio2含量为65%，是过去500年来圣海伦火山喷发的岩浆中二氧化硅含量最丰富、不相容元素含量最低的。自从第一个熔岩脊出现后不久，就开始用悬挂在直升机下方20-35米处的钢箱挖泥船（“大白鲨”）收集样本，偶尔也用手工取样。截至2006年春天，已经从新熔岩圆顶的七个脊椎中收集了25个年龄控制的样本。样品取自棘的内部和甲壳，由断层泥和碎裂岩组成，厚度为1 ~ 2 m。英安岩熔岩结晶丰富，有40- 50%的斑晶。地面物质广泛结晶为石英、三晶石和富钠钾长石微晶的共晶组合，在无囊泡的基础上，除最早喷发的外，所有喷发的总晶体含量均超过80%。
Eighteen years after dome-forming eruptions ended in 1986, and with little warning, Mount St. Helens began to erupt again in October 2004. During the ensuing two years, the volcano extruded more than 80×10 6 m 3 of gas-poor, crystal-rich dacite lava. The 2004-6 dacite is remarkably uniform in bulk-rock composition and, at 65 percent SiO 2 , among the richest in silica and most depleted in incompatible elements of the magmas erupted at Mount St. Helens during the past 500 years. Since shortly after the first spine of lava appeared, samples have been collected using a steel box dredge ("Jaws") suspended 20-35 m below a helicopter and, occasionally, by hand sampling. As of the spring of 2006, 25 age-controlled samples have been collected from the seven spines of the new lava dome. Samples were obtained from both the interiors of spines and from their carapaces, which are composed of fault gouge and cataclasite 1-2 m thick. The dacite lava is crystal rich, with 40-50 percent phenocrysts. The groundmass is extensively crystallized to a cotectic assemblage of quartz, tridymite, and Na- and K-rich feldspar microlites, raising the total crystal content to more than 80 percent on a vesicle-free basis in all but the earliest erupted.