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Petrology of the April 2015 eruption of Calbuco volcano, southern Chile
Journal of Petrology ( IF 3.9 ) Pub Date : 2020-08-01 , DOI: 10.1093/petrology/egaa084
Olivier Namur 1, 2 , Salvatrice Montalbano 2 , Olivier Bolle 2 , Jacqueline Vander Auwera 2
Affiliation  

Understanding the origin of intermediate magmas that commonly erupt from subduction zone volcanoes is important to better constrain the mechanisms of continental crust formation. We carried out a detailed mineralogical and petrological study of the eruptive products from the last eruption of Calbuco volcano, Chile. In April 2015, Calbuco produced a 3 phase sub-Plinian eruption with pyroclastic fallouts and flows of andesitic composition. Rocks from Calbuco are made up of a glass phase and a high but variable proportion of minerals dominated by plagioclase, clinopyroxene, orthopyroxene and minor olivine, amphibole and magnetite. Plagioclase is very strongly zoned with highly anorthitic cores surrounded by more albitic rims. Based on thermodynamic calculations and using published experimental data, we estimate that the anorthitic cores crystallized from a basaltic andesite containing 3.5-4.5 wt.% H 2 O. Using geochemical modelling, we also estimate that the bulk-rock major and trace element variability of Calbuco is best explained by accumulation of minerals in proportion plagioclase/pyroxene 72/28 in a dacitic melt. Such minerals most likely formed in the crystal mush zone of a magma chamber which, according to pyroxene and amphibole compositions, may have formed at a pressure of 2-3 kbar, corresponding to a depth of 8-11 km. A few weeks to months before the eruption, the crystal mush disaggregated, perhaps due to magmatic underplating, and a crystal-bearing dacitic melt moved upwards into a sub-surface storage region where the anorthite-poor rims formed. The 2015 eruption was probably internally triggered by over-pressurization in the shallow magma chamber.

中文翻译:

2015 年 4 月智利南部卡尔布科火山喷发的岩石学

了解通常从俯冲带火山喷发的中间岩浆的起源对于更好地限制大陆地壳形成机制很重要。我们对智利卡尔布科火山上次喷发的喷发产物进行了详细的矿物学和岩石学研究。2015 年 4 月,Calbuco 产生了一个 3 阶段的亚普林尼亚火山喷发,带有火山碎屑沉降物和安山岩成分流。Calbuco 的岩石由玻璃相和大量但可变比例的矿物组成,主要是斜长石、斜辉石、斜方辉石和少量橄榄石、角闪石和磁铁矿。斜长石被非常强烈地划分为高度斜长石核心被更多的白长石边缘包围。基于热力学计算并使用已发表的实验数据,我们估计从含有 3.5-4.5 wt.% H 2 O 的玄武质安山岩结晶的斜长岩核。使用地球化学模型,我们还估计 Calbuco 的块状岩石主要和微量元素变异性最好通过矿物按比例的积累来解释斜长石/辉石 72/28 在英安熔体中。此类矿物最有可能形成于岩浆房的结晶糊状带,根据辉石和闪石的成分,其可能在 2-3 kbar 的压力下形成,对应于 8-11 公里的深度。在喷发前几周到几个月,可能是由于岩浆底沉积,晶体糊状物解体,含晶体的英安质熔体向上移动到地下储存区域,在那里形成了贫钙长石边缘。
更新日期:2020-08-01
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