Measuring the degree of "nanotilization" of volcanic glasses: Understanding syn-eruptive processes recorded in melt inclusions
Measuring the degree of "nanotilization" of volcanic glasses: Understanding syn-eruptive processes recorded in melt inclusions
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DOI：
10.1016/j.lithos.2018.08.011
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发表时间：
2018-10-01
期刊：
影响因子：
3.5
通讯作者：
Kolzenburg, Stephan
中科院分区：
文献类型：
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作者：
Di Genova, Danilo;Caracciolo, Alberto;Kolzenburg, Stephan
铁和水的含量大大影响天然硅酸盐熔体的物理性质，因此，可能会影响岩浆和火山过程，如结晶，脱气，流动行为和喷发风格。在这里，我们提出了拉曼光谱数据的一组合成和天然的多组分玻璃具有不同的铁氧化态和水含量。我们系统地研究了不同的拉曼激发源的光谱响应的无晶体和磁铁矿纳米轴承玻璃跨越玄武岩钙和过碱性流纹岩组成的影响。基于这些数据，我们记录的拉曼光谱的变化所产生的纳米级晶体的形成。我们发现，位于970 cm（-1）附近的峰与淬火熔体结构中溶解的Fe 2 O3的存在直接相关，并且无论样品的化学组成和拉曼激发源如何，该特征都存在。我们进一步表明，在670和690 cm（-1）之间的峰，这是不相关的任何其他光谱特征的玻璃结构，揭示了纳米晶体的存在。基于系统的光谱调查，这一功能，我们提出了一个新的指数，允许识别铁是否存在于纳米晶状态和/或绑定在玻璃结构。由于熔体的结构和物理效应的形成纳米玻璃可以严重影响熔体的流动行为和火山的喷发风格，在这项研究中提出的结果显着拓宽了应用拉曼光谱的纳米异质性的调查合成和天然玻璃。我们应用这种方法来研究纳米化的程度，以及H2O含量和铁的氧化态的基质玻璃，以及熔体包裹体和玻璃湾从潘泰莱里亚岛（意大利）的爆炸产品。我们观察到，纳米化的过程并不纯粹局限于磁铁矿纳米化，但拉曼光谱也可以确定辉石和长石在亚微米尺度的初期结晶。数据文件表明，纳米石的形成与观察到的强度的各自的喷发表明，在熔体中的结构变化，初期结晶所造成的定义相对低粘度岩浆的喷发风格中发挥了重要作用。(C)2018作者由爱思唯尔公司出版
Iron and water content substantially affect the physical properties of natural silicate melts and may, therefore, influence magmatic and volcanic processes such as crystallization, degassing, flow behaviour and eruptive style. Here we present Raman spectroscopic data for a set of synthetic and natural multicomponent glasses with varying iron oxidation state and water content. We systematically study the effect of different Raman excitation sources on the spectral response of both crystal free and magnetite nanolite bearing glasses spanning basaltic to calc- and per-alkaline rhyolitic compositions. Based on these data we document changes in Raman spectra resulting from the formation of nano-scale crystals. We show that the peak located at similar to 970 cm(-1) is directly related to the presence of Fe2O3 dissolved in the quenched melt structure and that this feature is present regardless of the chemical composition of the sample and the Raman excitation source. We further show that a peak between 670 and 690 cm(-1), which is not related to any other spectral feature of the glass structure, reveals the presence of nanolites. Based on systematic spectral investigations of this feature, we present a new index that allows to identify if iron is present in the nanocrystalline state and/or bound in the glass structure. Since the melt structural and physical effects of the formation of nanolites can heavily affect the flow behaviour of melts and the eruptive style of volcanoes, the results presented in this study significantly broaden the application of Raman spectroscopy for investigations of nano-heterogeneity in synthetic and natural glasses. We apply this method to study both the degree of nanolitization as well as the H2O content and iron oxidation state of groundmass glasses as well as melt inclusions and glass embayments in explosive products from Pantelleria island (Italy). We observe that the process of nanotilization is not purely restricted to magnetite nanolites but that Raman spectroscopy may also identify the incipient crystalization of pyroxene and feldspar at sub-micron scale. The data document that nanolite formation correlates well with the observed intensity of the respective eruptions suggesting that structural changes in the melt, caused by incipient crystallization play an important role in defining the eruptive style of relatively low viscosity magmas. (C) 2018 The Authors. Published by Elsevier B.V.