Explosive style, magma degassing and evolution in the Chaimilla eruption, Villarrica volcano, Southern Andes
Explosive style, magma degassing and evolution in the Chaimilla eruption, Villarrica volcano, Southern Andes
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安第斯山脉南部比亚里卡火山 Chaimilla 喷发的爆炸方式、岩浆脱气和演化
DOI：
10.1007/s00445-015-0976-1
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发表时间：
2015
影响因子：
3.5
通讯作者：
Jorge Clavero
中科院分区：
文献类型：
--
作者：
L. Pioli;L. Scalisi;L. Costantini;A. D. Muro;C. Bonadonna;Jorge Clavero
维拉里卡(智利)是一座玄武岩层状火山，目前处于明渠状态。它现在有相对频繁的斯特龙博尔式喷发和热情洋溢的喷发，但在史前时代有过大规模的爆炸性喷发。其中，最近的一次喷发是查米利亚火山喷发，它发生在大约3100年前，产生的沉积物表明了复杂的多期喷发动力学。喷发的火山渣的矿物学和玻璃成分的显著差异表明，喷发是由两批不同的岩浆提供的，它们的主体成分相似，但结晶和脱气历史不同。下层序Score具有复杂的晶体组合，有几个晶群，由相对脱气的含有Fo75-79橄榄石的岩浆、正常或反向分带的斜长石(An70-94)和辉石(I型岩浆)与从属体积的更原始、更富挥发分的岩浆混合而成，这些岩浆从深处升起(第2类岩浆)，并携带正常分带的斜长石和高镁(Fo81-85)橄榄石晶体。第二类岩浆是沉积上层序的更大、更具爆炸性的喷发阶段释放的主要成分。柴米拉火山喷发发生在封闭的喷口条件下，由富含水的岩浆提供。与目前在维拉里卡喷发的岩浆的岩石学特征相比，这些结果表明，火山喷发方式从高爆炸性向熔岩湖/闪电活动的演化对应于浅层管道系统(现在位于更浅的深度)的显著变化；这些管道系统的变化与母岩浆成分的重大变化无关。
Villarrica (Chile) is a basaltic stratovolcano, currently in an open-conduit condition. It now has relatively frequent Strombolian and effusive eruptions, but it had large explosive eruptions in prehistoric times. Among them, the most recent eruption was Chaimilla, which occurred about 3100 years ago and produced deposits that indicate complex, multiphase eruptive dynamics. Significant differences in mineralogy and glass compositions of the erupted scoria suggest the eruption was fed by two distinct magma batches with similar bulk compositions but distinct crystallization and degassing histories. The lower sequence scoria has a complex crystal assemblage with several crystal populations produced by mixing between a relatively degassed magma containing Fo75-79 olivine, normally or reversely zoned plagioclase (An70-94) and augite (type 1 magma), and a subordinate volume of more-primitive and more volatile-rich magma rising from depth (type 2 magma) and carrying normally zoned plagioclase and higher-Mg (Fo81-85) olivine crystals. Type 2 magma was the main component emitted during the larger and more explosive eruptive phase that deposited the upper sequence. The Chaimilla eruption occurred under closed-vent conditions and was fed by water-rich magmas. When compared with the petrological features of the magma currently erupted at Villarrica, which has slightly more-evolved bulk compositions, lower crystal content and lower water content, these results suggest that the evolution in eruptive style of the volcano from highly explosive to a lava lake/Strombolian activity corresponds to significant changes in the shallow plumbing system (which is now at much shallower depths); these plumbing-system changes were not associated with significant changes in the parental magma compositions.