The 2013 eruption of Chaparrastique volcano (El Salvador): Effects of magma storage, mixing, and decompression
The 2013 eruption of Chaparrastique volcano (El Salvador): Effects of magma storage, mixing, and decompression
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DOI：
10.1016/j.chemgeo.2016.11.015
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发表时间：
2017-01
期刊：
影响因子：
3.9
通讯作者：
P. Scarlato;S. Mollo;E. Bello;A. Quadt;Richard J. Brown;E. Gutiérrez;B. Martinez-Hackert;P. Papale
中科院分区：
文献类型：
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作者：
P. Scarlato;S. Mollo;E. Bello;A. Quadt;Richard J. Brown;E. Gutiérrez;B. Martinez-Hackert;P. Papale
2013年12月29日，萨尔瓦多查帕拉斯蒂克火山（Chaparrastique）在沉寂12年后发生了一次孤立的火山喷发。这次喷发被归类为VEI 2级，并产生了最大高度约9公里的火山灰羽。火山喷发产物斑晶的结构和成分数据与大块岩石的地球化学和同位素信息相结合，阐明了火山活动重新觉醒的岩浆过程。富磷橄榄石与高镁钛磁铁矿共生，贫磷橄榄石与低镁钛磁铁矿共生。矿物-熔体平衡表明，弧系下地壳中典型的高t（~ 1130 ~ 1150℃）含fo2 （NNO缓冲液）的玄武岩岩浆与较浅、氧化程度较高的地壳储层中常见的低t（~ 1060 ~ 1080℃）含fo2 （NNO + 1缓冲液）的玄武岩安山岩岩浆混合形成了不同的斑晶群。在相对低p （~ 150 ~ 250 MPa）和低t（~ 1000 ~ 1050℃）下，基于正斜辉石和斜辉石之间Fe-Mg交换的热气压测量限制了喷发前的结晶。两种化学性质截然不同的岩浆之间的混合作用，还表现为反向分带斜长石斑晶的出现，这些斑晶具有被吸收的钠质岩心，以及筛状结构钙幔的重新生长。相反，斜长石边缘表现出不平衡成分，这与岩浆快速上升到地表（~ 0.03 m/s）所驱动的减压动力学（~ 10−3MPa/s）有关。主要元素和微量元素模拟排除了分离结晶作为控制大块岩石变异性的主要机制，而地球化学数据则显示了原始玄武岩和分异玄武岩安山岩两个端元之间的混合趋势。微量元素和同位素数据表明，岩浆活动的主要来源是由俯冲板块产生的交代流体和/或熔体通量贡献的富集的morb类地幔。来自半深海沉积物的碳酸盐源的板状流体输入和板状熔体所起的作用似乎很小。岩浆被地壳岩石同化/污染的过程也可以忽略不计。相比之下，岩浆的地球化学特征受到主要由海洋沉积物和蚀变玄武岩地壳逐渐脱水产生的板源含水流体的极大影响。
On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12 years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~ 9 km. Textural and compositional data from phenocrysts from the erupted products have been integrated with geochemical and isotopic information from bulk rocks to elucidate the magmatic processes responsible for the reawakening of volcanic activity.Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites. Mineral-melt equilibria suggest an origin for the distinct phenocryst populations by mixing between a high-T(~ 1130–1150 °C), basaltic magma withfO2(NNO buffer) typical of the lower crust in arc systems and a low-T(~ 1060–1080 °C), basaltic andesitic magma withfO2(NNO + 1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg exchange between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low-P(~ 150–250 MPa) and low-T(~ 1000–1050 °C). Mixing between two chemically distinct magmas is also evidenced by the occurrence of reverse zoned plagioclase phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcic mantles. Conversely, plagioclase rims exhibit disequilibrium compositions addressed to decompression kinetics (~ 10− 3MPa/s) driven by rapid magma ascent to the surface (~ 0.03 m/s).Major and trace element modelling excludes fractional crystallization as the primary mechanism controlling the bulk rock variability, whereas geochemical data align along a mixing trend between two end-members representative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes of metasomatic fluids and/or melts produced by the subducted slab. The role played by slab-fluid inputs of carbonate origin and slab-melts from the hemipelagic sediments seems to be minimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influenced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crust.