Geology and petrology of ejecta from the 1999 eruption of Shishaldin Volcano, Alaska
Geology and petrology of ejecta from the 1999 eruption of Shishaldin Volcano, Alaska
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DOI：
10.1007/s00445-002-0229-y
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发表时间：
2002-12
影响因子：
3.5
通讯作者：
P. Stelling;J. Beget;C. Nye;J. Gardner;J. Devine;R. George
中科院分区：
文献类型：
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作者：
P. Stelling;J. Beget;C. Nye;J. Gardner;J. Devine;R. George
1999年4月和5月期间，希沙尔丁火山多次喷发，4月19日和23日发生重大喷发事件。20厘米厚的Tephra沉积物分布在南部侧翼，高度集中的泥石流沿着北部斜坡流下。所有分析的碎屑成分都是玄武岩，含有丰富的(~29%)斜长石、橄榄石和磁铁矿斑晶。玻璃包裹体分析显示低挥发分(<；1.5wt%)，NNO+1的氧逸度，以及从接近饱和到高度不饱和的高度可变的S水平(分别为>；900至58ppm)。对玻璃包裹体和基质玻璃中硫含量的比较表明，甚至在喷发之前就已经发生了大量的脱气。微量元素研究表明，石沙尔丁以下的岩浆库可能不是一个封闭的、长寿命的洞室，U-Th-Ra同位素分析表明，1999年产物的地壳停留时间很短(最多几千年)。将这次喷发的沉积物与其他类似规模的喷发进行比较，表明4月19日的爆炸事件应被归类为次普林尼期玄武岩喷发。这样的喷发很少见。4月19日的爆炸事件是希沙尔丁过去175年来最大的爆炸事件。然而，岩石学、化学和沉积物厚度及分布与过去9000多年来至少11个斯科石矿床相似，这表明这种类型的喷发在Shishaldin是常见的。
Shishaldin Volcano erupted repeatedly during April and May 1999, with major eruptive events on 19 April and 23 April. Tephra deposits >20 cm thick were distributed across the southern flanks and hyperconcentrated debris flows ran down the northern slope. All analyzed clasts were basaltic in composition, with abundant (~29 vol%) phenocrysts of plagioclase, olivine, and magnetite. Glass-inclusion analyses indicate low volatile contents (<1.5 wt%), oxygen fugacity of NNO+1, and highly variable S levels ranging from near saturation to highly undersaturated (>900 to 58 ppm, respectively). Comparisons of sulfur contents in glass inclusions and groundmass glasses suggest significant degassing occurred even prior to eruption. Trace-element studies suggest that the magma reservoir below Shishaldin may not be a closed, long-lived chamber, and U–Th–Ra isotopic analyses indicate short crustal residence times (on the order of at most a few thousand years) for the 1999 products. Comparison of the deposits from this eruption with other similarly sized eruptions suggests the 19 April explosive event should be classified as a sub-Plinian basaltic eruption. Such eruptions are rare. The 19 April explosive event was the largest at Shishaldin during the last 175 years. However, the petrology, chemistry and deposit thickness and distribution resemble those of at least 11 scoria deposits in the last 9,000 years, suggesting that this type of eruption is common for Shishaldin.