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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Reconstructing CO2 concentrations in basaltic melt inclusions using Raman analysis of vapor bubbles
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Reconstructing CO2 concentrations in basaltic melt inclusions using Raman analysis of vapor bubbles

机译：利用气泡的拉曼分析重建玄武质熔体中的二氧化碳浓度

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Melt inclusions record valuable information about pre-eruptive volatile concentrations of melts. However, a vapor bubble commonly forms in inclusions after trapping, and this decreases the dissolved CO2 concentration in the melt (glass) phase in the inclusion. To quantify CO2 loss to vapor bubbles, Raman spectroscopic analysis was used to determine the density of CO2 in bubbles in melt inclusions from two Cascade cinder cones near Mt. Lassen and two Mexican cinder cones (Jorullo, Paricutin). Using analyses of dissolved CO2 and H2O in the glass in the inclusions, the measured CO2 vapor densities were used to reconstruct the original dissolved CO2 contents of the melt inclusions at the time of trapping. Our results show that 30-90% of the CO2 in a melt inclusion is contained in the vapor bubble, values similar to those found in other recent studies. We developed a model for vapor bubble growth to show how post-entrapment bubbles form in melt inclusions as a result of cooling, crystallization, and eruptive quenching. The model allows us to predict the bubble volume fraction as a function of Delta T (the difference between the trapping temperature and eruptive temperature) and the amount of CO2 lost to a bubble. Comparison of the Raman and modeling methods shows highly variable agreement. For 10 of 17 inclusions, the two methods are within +/- 550 ppm CO2 (avg. difference 290 ppm), equivalent to +/-similar to 300 bars uncertainty in estimated trapping pressure for restored inclusions. Discrepancies between the two methods occur for inclusions that have been strongly affected by post-entrapment diffusive H+ loss, because this process enhances bubble formation. For our dataset, restoring the CO2 lost to vapor bubbles increases inferred trapping pressures of the inclusions by 600 to as much as 4000 bars, highlighting the importance of accounting for vapor bubble formation in melt inclusion studies. (C) 2016 Elsevier B.V. All rights reserved.
机译：熔体夹杂物记录了有关喷发前熔体挥发物浓度的重要信息。但是，夹杂物后通常会在夹杂物中形成蒸气泡，这会降低夹杂物的熔融（玻璃）相中的溶解CO2浓度。为了量化CO2损失到气泡中，使用拉曼光谱分析法确定了Mt附近两个Cascade煤渣锥中熔体夹杂物中气泡中CO2的密度。拉森和两个墨西哥煤渣锥（朱利洛，帕里库丁）。通过对夹杂物中玻璃中溶解的CO2和H2O的分析，所测得的CO2蒸气密度被用于重建捕集时熔融夹杂物的原始溶解CO2含量。我们的结果表明，熔体夹杂物中30-90％的CO2包含在气泡中，其值与其他最近的研究相似。我们开发了一个蒸汽气泡生长模型，以显示由于冷却，结晶和喷发淬火而在熔融夹杂物中形成包埋后气泡的方式。该模型使我们能够预测气泡体积分数随Delta T（捕集温度和喷发温度之间的差）和气泡损失的CO2量的函数。拉曼和建模方法的比较显示出高度可变的一致性。对于17个夹杂物中的10个，这两种方法均在+/- 550 ppm CO2之内（平均差290 ppm），相当于+/-类似于恢复的夹杂物的估计捕集压力的300 bar不确定度。两种方法之间的差异发生在夹杂物受捕集后扩散H +损失严重影响的情况下，因为此过程会增加气泡的形成。对于我们的数据集，恢复损失到气泡中的二氧化碳会使推断的夹杂物捕获压力增加600至多达4000 bar，这凸显了在熔体夹杂物研究中考虑气泡形成的重要性。 （C）2016 Elsevier B.V.保留所有权利。

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