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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Evolution of magma feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan
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Evolution of magma feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan

机译：日本东北藏王火山熊野岳凝集活动中岩浆供给系统的演变

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The Kumanodake agglutinate of Zao Volcano in northeastern japan consists of pyroclastic surge layers accumulated during the early part of the newest stage of activity (ca. 33 ka to present). Our petrologic study of this agglutinate based on systematically collected samples aims to reveal the evolution of magma feeding system. To understand the magma evolution, we have examined samples from the agglutinate by using petrologic data including, petrography, analysis of minerals (plagioclase, pyroxene, and olivine), glass compositions, and whole rock major element and trace element (Ba, Sr, Cr, Ni, V, Rb, Zr, Nb, and Y) compositions. Agglutinate are mixed, medium-K, calc-alkaline olv-cpx-opx basaltic andesite (552-56.2% SiO2). Results show that the magma feeding system comprised a shallow felsic chamber injected by mafic magma from depth. The felsic magma (59-62% SiO2, 950-990 degrees C), which was stored at a shallower depth, had orthopyroxene (Mg# = 60-69), clinopyroxene (Mg# = 65-71), and low-An plagioclase (An(ca.) (58-70)). The mafic magma is further divisible into two types: less-differentiated and more-differentiated, designed respectively as an initial mafic magma-1 and a second mafic magma-2. The original mafic magma-1 was olivine (Fo(similar to 84)) basalt (ca. 48-51% SiO2, 1110-1140 degrees C). The second mafic magma-2, stored occasionally at 4-6 km depth, was basalt (1070-1110 degrees C) having Fo(ca. 80) olivine and high-An (An(ca.) (90)) plagioclase phenocrysts. These two magmas mixed (first mixing) to form hybrid mafic magma. The forced injections of the hybrid mafic magmas activated the felsic magma, and these two were mixed (second mixing) shortly before eruptions. The explosivity is inferred to have increased over time because the abundance of large scoria increased. Furthermore, the erupted magma composition became more mafic, which reflects increased percentage of the hybrid mafic magma involved in the second mixing. At the beginning of activity, the mafic magma also acted as a heat source for activation of the felsic magma chamber, thereby suppressing the volume percentage of mafic magma in the mixing. As the activity proceeded thereafter, the shallow felsic chamber would become more mobile. Consequently, the hybrid mafic magma would be able to mix with felsic magmas more easily, resulted in higher percentage of the hybrid mafic magma in the mixing. (C) 2015 Elsevier B.V. All rights reserved.
机译：日本东北部Zao火山的Kumanodake凝集物由在最新活动阶段的早期（约33 ka至今）积累的火山碎屑涌浪层组成。我们基于系统收集的样本对该凝集物的岩石学研究旨在揭示岩浆饲喂系统的演变。为了了解岩浆的演化，我们通过使用岩石学数据（包括岩石学，矿物（斜长石，辉石和橄榄石）的矿物学分析，玻璃成分以及整个岩石的主要元素和微量元素（Ba，Sr，Cr， （Ni，V，Rb，Zr，Nb和Y）组成。凝集酸盐是混合的，中等K的钙碱性olv-cpx-opx玄武质安山岩（552-56.2％SiO2）。结果表明，岩浆供给系统由浅部岩浆室构成，基岩浆从深部注入。浅层岩浆（59-62％SiO2，950-990摄氏度）储存在较浅的深度，具有邻苯二茂铁（Mg＃= 60-69），斜rox石（Mg＃= 65-71）和低An斜长石（An（ca。）（58-70））。铁镁质岩浆可进一步分为两种：低分化和高分化，分别设计为初始镁铁质岩浆1和第二镁铁质岩浆2。最初的镁铁质岩浆1是橄榄石（Fo（类似于84））玄武岩（约48-51％SiO2,1110-1140摄氏度）。第二镁铁质岩浆2偶尔存储在4-6 km的深度，是玄武岩（1070至11010摄氏度），具有Fo（ca。80）橄榄石和高An（An（ca。）（90））斜长石型隐晶岩。这两个岩浆混合（第一次混合）形成混合镁铁质岩浆。强迫注入混合铁镁铁质岩浆激活了长英质岩浆，并且在喷发前不久将两者混合（第二次混合）。推断爆炸性随时间增加，因为大炉渣的数量增加了。此外，喷出的岩浆成分变得更加镁铁质，这反映出第二次混合中混合的镁铁质岩浆的百分比增加。在活动开始时，铁镁质岩浆还充当激活长笛岩浆室的热源，从而抑制了混合过程中铁镁质岩浆的体积百分比。随着此后活动的进行，浅长肌室将变得更加活动。因此，混合镁铁质岩浆将能够更容易地与长英质岩浆混合，导致混合镁铁质岩浆在混合中的比例更高。 （C）2015 Elsevier B.V.保留所有权利。

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