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首页> 外文期刊>Contributions to Mineralogy and Petrology >The geochemical and petrological characteristics of prenatal caldera volcano: a case of the newly formed small dacitic caldera, Hijiori, Northeast Japan
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The geochemical and petrological characteristics of prenatal caldera volcano: a case of the newly formed small dacitic caldera, Hijiori, Northeast Japan

机译：产前普尔康达火山火山的地球化学和岩石学特征 - 以新成型的小型巨大的小巨毛山，Hijiori，日本东北

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Evaluating the magma depth and its physical properties is critical to conduct a better geophysical assessment of magma chambers of caldera volcanoes that may potentially cause future volcanic hazards. To understand pre-eruptive conditions of a magma chamber before its first appearance at the surface, this paper describes the case of Hijiori caldera volcano in northeastern Japan, which emerged approximately 12,000 years ago at a place where no volcano ever existed. We estimated the depth, density, bulk modulus, vesicularity, crystal content, and bulk H2O content of the magma chamber using petrographic interpretations, bulk and microchemical compositions, and thermodynamic calculations. The chemical mass balance calculations and thermodynamic modeling of the erupted magmas indicate that the upper portion of the Hijiori magmatic plumbing system was located at depths between 2 and 4 km, and had the following characteristics: (1) pre-eruptive temperature: about 780. C; (2) bulk magma composition: 66 +/- 1.5 wt% SiO2; (3) bulk magmatic H2O: approximately 2.5 wt%, and variable characteristics that depend on depth; (4) crystal content: <= 57 vol%; (5) bulk modulus of magma: 0.1-0.8 GPa; (6) magma density: 1.8-2.3 g/cm(3); and (7) amount of excess magmatic H2O: 11-32 vol% or 48-81 mol%. The range of melt water contents found in quartz-hosted melt inclusions (2-9 wt%) suggests the range of depth phenocrysts growth to be wide (2 similar to 13 km). Our data suggest the presence of a vertically elongated magma chamber whose top is nearly solidified but highly vesiculated; this chamber has probably grown and re-mobilized by repeated injections of a small amount of hot dacitic magma originated from the depth.
机译：评估岩浆深度及其物理性质对于对可能导致未来的火山危害可能导致的火山岩火山的岩浆室进行更好的地球物理评估至关重要。要了解岩浆室的预先发生条件，在其表面的第一个外观之前，本文介绍了日本东北部的Hijiori Caldera火山的案例，大约有12,000年前在一个没有火山的一个地方出现。我们估计了使用岩体解释，散装和微型化组合物和热力学计算岩浆室的深度，密度，散装量，糊状性，晶体含量和大量H2O含量，以及热力学计算。爆发的岩浆的化学质量平衡计算和热力学建模表明，Hijiori岩浆管道系统的上部位于2到4公里的深度，具有以下特点：（1）预喷发温度：约780。 C; （2）散装岩浆组成：66 +/- 1.5重量％SiO2; （3）散装岩岩H2O：约2.5wt％，依赖深度的可变特征; （4）晶体含量：<= 57体积％; （5）岩浆的散装模量：0.1-0.8 GPA; （6）岩浆密度：1.8-2.3 g / cm（3）; （7）多余岩浆H2O的量：11-32体积％或48-81摩尔％。在石英托管熔体夹杂物中发现的熔融水含量（2-9wt％）表明宽度的深度生长的范围（2类似于13公里）。我们的数据建议存在垂直细长的岩浆室，其顶部几乎凝固但高度囊泡;该腔室可能通过重复喷射少量的热磁石岩浆来生长并重新调动源自深度。

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