Magma plumbing system beneath Ontake Volcano, central Japan
Magma plumbing system beneath Ontake Volcano, central Japan
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DOI：
10.1046/j.1440-1738.1999.00219.x
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发表时间：
1999-03
期刊：
影响因子：
1.5
通讯作者：
J. Kimura;Takeyoshi Yoshida
中科院分区：
文献类型：
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作者：
J. Kimura;Takeyoshi Yoshida
日本中部的御岳火山最后一次活跃是在 100–35 Ka 左右。第一阶段喷发含有流纹英安石浮石和熔岩（O1阶段，> 33 km3），随后喷发安山岩熔岩和火山碎屑岩（O2和O3阶段，> 16 km3）。对主要元素和不相容元素与 Sr 同位素比的建模表明，原生岩浆是高铝玄武岩。一种安山岩岩浆类型似乎是从封闭系统岩浆室中的玄武岩演化而来，部分是通过分步结晶作用，其生成包括地壳同化。另一种安山岩岩浆类型被认为是在开放系统的岩浆房中演化的，其中原生岩浆反复输入，同时发生围岩同化和分异结晶。推测流纹英安岩是在封闭系统岩浆房中通过第二类安山岩的分步结晶而演化出来的。这些遗传关系要求岩浆室作为开放系统和封闭系统交替发挥作用。地压测量表明可能存在多个岩浆房，对于流英安岩来说位于上地壳，对于安山岩来说位于上地壳与下地壳界面附近，对于玄武岩来说位于中下地壳。这些房间堆叠起来形成了御岳的岩浆管道系统。玄武岩的不相容元素组成被认为在喷发过程中发生了变化，这表明在 65 Ka 活动期间存在 O1 阶段岩浆和 O2、O3 阶段岩浆的两种不同的管道系统。这些系统的演化历史表明，原生岩浆被引入岩浆管道系统的时间约为 17 500 年，并且岩浆管道系统的寿命短于 40 Ka。
Ontake Volcano in central Japan was last active from ~ 100–35 Ka. The eruptions contained rhyodacite pumice and lavas in the first stage (stage O1, > 33 km3), followed by eruptions of andesite lavas and pyroclastics (stages O2 and O3, > 16 km3). Modeling of major and incompatible elements with Sr isotope ratios suggests that the primary magma was a high‐alumina basalt. One andesite magma type appears to have evolved from the basalt in a closed system magma chamber, in part by fractional crystallization, and its generation included crustal assimilation. The other andesite magma type is considered to have evolved in an open system magma chamber in which repeated input of primary magma occurred together with wall‐rock assimilation and fractional crystallization. The rhyodacite is inferred to have evolved in a closed system magma chamber by fractional crystallization of the second type of andesite. These genetic relationships require that the magma chamber functioned alternately as an open and a closed system. Geobarometry indicates that there may have been multiple magma chambers, located in the upper crust for the rhyodacite, near the upper–lower crust interface for the andesite and in the mid‐lower crust for the basalt. These chambers were stacked to form the magma plumbing system of Ontake. Incompatible element compositions of the basalt are considered to have changed during the eruptions, suggesting that two different plumbing systems for stage O1 magma and for stages O2, O3 magmas existed during the 65 Ka of activity. Evolutionary history of the systems implies that the primary magma was introduced into the magma plumbing system each for ~ 17 500 years and that the life span of a magma plumbing system was shorter than 40 Ka.