Mafic magma injection triggers eruption at Ilopango Caldera, El Salvador, Central America
Mafic magma injection triggers eruption at Ilopango Caldera, El Salvador, Central America
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镁铁质岩浆注入引发中美洲萨尔瓦多伊洛潘戈火山口喷发
DOI：
10.1130/0-8137-2375-2.175
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发表时间：
2004
影响因子：
3.9
通讯作者：
J. Stix
中科院分区：
文献类型：
--
作者：
M. Richer;C. P. Mann;J. Stix
伊洛潘戈火山口最近的活动发生在1880年，当时一个英安质熔岩圆顶（68.4重量% SiO2）从火山口湖中心出现。玄武安山岩（53.9wt%SiO2）的深色内含物占英安岩圆顶的2%至3%（体积）。岩石学结构和地球化学特征表明，镁铁质包裹体是注入部分结晶的英安岩岩浆后凝固形成的。在凝固过程中和凝固前，英安岩中观察到的斜长石晶体主动转移到镁铁质岩浆中，夹带英安岩熔体并在晶体上产生反应边缘。在镁铁质包裹体中，常见的斜长岩晶体具有钠质核心（An 40 -50）和更多的钙增生边缘（~ An 70），它们来自英安质熔体。紧密混合的英安岩玻璃表现出小，但显着的化学差异相对于主机英安岩，最显着的钾富集，我们归因于两个magas.We之间的扩散过程中提出的注入镁铁质岩浆在部分结晶英安岩岩浆的基础上引发了1880年的喷发。喷发所需的超压是由镁铁质岩浆的加入产生的，它触发了上升英安岩的泡状化。在公元429年和1880年的喷发中都存在镁铁质岩浆，这可能表明这一过程在伊洛潘戈的喷发历史中具有普遍的重要性。
The most recent activity at Ilopango Caldera occurred in 1880 when a dacitic lava dome (68.4 wt% SiO2) emerged from the center of the caldera lake. Dark inclusions of basaltic andesite (53.9 wt% SiO2) represent 2 to 3 vol% of the dacite dome. Petrographic textures and geochemistry indicate that the mafic inclusions were solidified after injection into partially crystallized dacite magma. During and before solidification, plagioclase crystals observed in the dacite actively transferred into the mafic magma, entraining dacitic melt and producing a reaction rim on crystals. Plagioclase crystals with sodic cores (An40–50) and more calcic overgrowth rims (~ An70) derived from the dacitic melt are common inside mafic inclusions. Intimately mingled dacitic glass exhibits small but significant differences in chemistry relative to the host dacite, most notably a potassium enrichment, which we attribute to diffusion processes between the two magmas.We propose that an injection of mafic magma at the base of partially crystallized dacite magma triggered the 1880 eruption. The overpressure necessary for eruption was generated by the addition of mafic magma, which triggered vesiculation of the rising dacite. The presence of mafic magma in both the AD 429 and 1880 eruptions may indicate that this process is of general importance in the eruptive history of Ilopango.