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首页> 外文期刊>Contributions to Mineralogy and Petrology >The effect of initial H2O concentration on decompression-induced phase separation and degassing of hydrous phonolitic melt
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The effect of initial H2O concentration on decompression-induced phase separation and degassing of hydrous phonolitic melt

机译：初始H2O浓度对减压诱导的相分离和含水发音熔体脱气的影响

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Supersaturation of H2O during magma ascent leads to degassing of melt by formation and growth of vesicles that may power explosive volcanic eruptions. Here, we present experiments to study the effect of initially dissolved H2O concentration (c(H2Oini)) on vesicle formation, growth, and coalescence in phonolitic melt. Vesuvius phonolitic melts with c(H2Oini) ranging between 3.3 and 6.3 wt% were decompressed at rates of 1.7 and 0.17 MPa center dot s(-1) and at temperatures >= 1323 K. Decompression started from 270 and 200 MPa to final pressures of 150-20 MPa, where samples were quenched isobarically. Optical microscopy and Raman spectroscopic measurements confirm that the glasses obtained were free of microcrystals and Fe-oxide nanolites, implying that the experiments were superliquidus and phase separation of the hydrous melt was homogeneous. A minimum number of the initially formed vesicles, defined by the number density normalized to vesicle-free glass volume (VND), is observed at 5 wt% c(H2Oini) with a logVND of 5 (in mm(-3)). The logVND increases strongly towards lower and higher c(H2Oini) by one order of magnitude. Furthermore, an important transition in evolution of vesiculation occurs at 5.6 wt% c(H2Oini). At lower c(H2Oini), the initial VND is preserved during further decompression up to melt porosities of 30-50%. At higher c(H2Oini), the initial vesicle population is erased at low melt porosities of 15-21% during further decompression. This observation is attributed to vesicle coalescence favored by low melt viscosity. In conclusion, c(H2Oini) determines the VND of initial phase separation and the evolution of vesiculation during decompression that controls the style of volcanic eruptions.
机译：Magma Ascent期间H2O的过饱和导致通过可能爆炸火山爆发的囊泡的形成和生长来脱气。在这里，我们提出了研究最初溶解的H2O浓度（C（H2OINI））对囊泡形成，生长和聚结中囊泡形成，生长和聚结作用的实验。在1.7和6.3wt％之间的C（H2OINI）的VESUVIUS发光物熔体在1.7和0.17MPa中心点S（-1）的速率下被解压缩> = 1323k。减压从270和200 MPa开始到最终压力150-20MPa，样品在异常淬火。光学显微镜和拉曼光谱测量结果证实，所得玻璃不含微晶和Fe氧化物纳米岩石，暗示实验是超脂质，含水熔体的相分离是均匀的。最初形成的初始形成的囊泡，由向无囊玻璃体积（VND）归一化的数量密度定义，在5wt％C（H 2 OINI）中，LOMVND为5（以mM（-3））。 LOGVND通过一个级别朝向更低和更高的C（H2OINI）强烈增加。此外，在5.6wt％C（H 2 OINI）中发生混血率的演化中的重要转变。在较低的C（H2OINI）中，在进一步减压期间保持初始VND以熔化孔隙率为30-50％。在较高的C（H 2 OINI）中，在进一步减压期间，在15-21％的低熔体孔隙中擦除初始囊泡群。该观察结果归因于低熔体粘度的囊泡聚结。总之，C（H2OINI）确定减压期间初始相分离的VND和对火山爆发风格的减压过程中的混血率的演变。

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