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首页> 外文期刊>Contributions to Mineralogy and Petrology >Intermittent mixing processes occurring before Plinian eruptions of Popocatepetl volcano, Mexico: insights from textural- compositional variations in plagioclase and Sr-Nd-Pb isotopes
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Intermittent mixing processes occurring before Plinian eruptions of Popocatepetl volcano, Mexico: insights from textural- compositional variations in plagioclase and Sr-Nd-Pb isotopes

机译：墨西哥Popocatepetl火山Plinian爆发之前发生的间歇性混合过程：斜长石和Sr-Nd-Pb同位素的结构-成分变化的见解

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Volcan Popocatepetl has explosively erupted in Plinian style at least five times in the last 23,000 years. Extreme deviations in composition and the occurrence of dissolution features in plagioclase and pyroxene, and the occasional presence of xenocrysts of Cr-rich Fe-Ti oxides and Mg-rich olivines and pyroxenes indicate that magma mixing has been a major process affecting the magmatic system. The nearly invariant composition of the erupted products (andesitic-dacitic) suggests, however, that mixing is not acting alone and must be balanced by assimilation and/or crystallization. To investigate the magmatic processes that have modified the Plinian magmas, textural and compositional variations and growth rates in plagioclase were used to approximate the frequency of mixing events affecting each magma. Systematic analysis of Sr, Nd, and Pb isotopes was carried out on plagioclase, pyroxene, and pumice matrix glass to constrain the extent of assimilation of upper crustal rocks. Additionally, a series of phase equilibrium experiments were carried out to constrain the depth where such mixing and assimilation occurred. We find that magma was stored at one of two different depths beneath Popocatepetl with magma mixing acting in both reservoirs. Mixing frequency and the relative impact on mineral compositions and textures has varied with time. Assimilation of calcareous rocks underneath Popocatepetl has not been pervasive and does not contribute significantly to the evolution of the Plinian magmas. The similar compositions of magmas with diverse mixing histories suggest that fractional crystallization, and possibly assimilation of deep crust, takes place at depth and that intermediate magmas ascend into the upper crust already differentiated.
机译：在过去的23,000年中，Volcan Popocatepetl至少以五次普林尼式爆发性爆发。斜长石和辉石的组成和溶出特征的极端偏差，以及富铬Fe-Ti氧化物，富镁的橄榄石和辉石的异晶相的偶尔出现，表明岩浆混合是影响岩浆系统的主要过程。但是，喷出产物（安第斯-大麦数）的组成几乎不变，这表明混合并不是单独起作用的，必须通过同化和/或结晶来平衡。为了研究改变普利尼岩浆的岩浆作用过程，斜长石的质地和成分变化以及增长率被用来估算影响每个岩浆的混合事件的频率。对斜长石，辉石和浮石基质玻璃进行了Sr，Nd和Pb同位素的系统分析，以限制上地壳岩石的同化程度。另外，进行了一系列相平衡实验以限制发生这种混合和同化的深度。我们发现岩浆储存在Popocatepetl下方两个不同深度之一，并且在两个储层中都有岩浆混合作用。混合频率以及对矿物成分和质地的相对影响随时间变化。 Popocatepetl下的钙质岩石同化作用尚未普及，并且对普利尼岩浆的演化没有显着贡献。具有不同混合历史的岩浆的相似组成表明，部分结晶和可能与深地壳同化发生在深处，而中间岩浆上升到已经分化的上地壳中。

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