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首页> 外文期刊>Geochemistry, geophysics, geosystems >Vesiculation in rhyolite at low H2O contents: A thermodynamic model
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Vesiculation in rhyolite at low H2O contents: A thermodynamic model

机译：低H2O含量的流纹岩中的成孔作用：热力学模型

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摘要

We present experimental data on the thermodynamics and kinetics of bubble nucleation and growth in weakly H2O-oversaturated rhyolitic melts. The high-temperature (900-1100 degrees C) experiments involve heating of rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland to above their glass transition temperature (Tg approximate to 690 degrees C) at 0.1 MPa for times of 0.25-24 h. During experiments, the rhyolite cores increase in volume as H2O vapor-filled bubbles nucleate and expand. The extent of vesiculation, as tracked by porosity, is mapped in temperature-time (T-t) space. At constant temperature and for a characteristic dwell time, the rhyolite cores achieve a maximum volume where the T-t conditions reach thermochemical equilibrium. For each T-t snapshot of vesiculation, we use 3-D analysis of X-ray computed tomographic (XCT) images of the quenched cores to obtain the bubble number density (BND) and bubble-size distribution (BSD). BNDs for the experimental cores are insensitive to T and t, indicating a single nucleation event. All BSDs converge to a common distribution, independent of T, melt viscosity (), or initial degree of saturation, suggesting a common growth process. We use these data to calibrate an empirical model for predicting the rates and amounts of vesiculation in rhyolitic melts as a function of and thermochemical affinity (A): two computable parameters that are dependent on T, pressure and H2O content. The model reproduces the experimental data set and data from the literature to within experimental error, and has application to natural volcanic systems where bubble formation and growth are not diffusion limited (e.g., lavas, domes, ignimbrites, conduit infill).
机译：我们目前的实验数据有关气泡成核和生长在弱H2O过饱和的流纹熔体中的热力学和动力学。高温（900-1100摄氏度）实验涉及将来自冰岛克拉夫拉的Hrafntinnuhryggur的流纹黑曜石在0.1 MPa的温度下加热至其玻璃化转变温度（Tg约为690摄氏度）以上，持续0.25-24小时。在实验过程中，流纹岩芯的体积随着H2O充满气泡的形核和膨胀而增加。孔隙度跟踪的气泡化程度在温度-时间（T-t）空间中绘制。在恒定的温度和特定的停留时间下，流纹岩芯在T-t条件达到热化学平衡时达到最大体积。对于每个T-t囊泡快照，我们对淬火后的核芯进行X射线计算机断层扫描（XCT）图像进行3-D分析，以获得气泡数密度（BND）和气泡尺寸分布（BSD）。实验核心的BND对T和t不敏感，表明发生了单个成核事件。所有BSD都收敛于一个共同的分布，而与T，熔体粘度（）或初始饱和度无关，这表明一个共同的生长过程。我们使用这些数据来校准经验模型，以预测流纹体熔体中囊泡形成的速率和数量与热化学亲和力（A）的关系：取决于T，压力和H2O含量的两个可计算参数。该模型可复制实验数据集和来自文献的数据至实验误差范围内，并可应用于气泡形成和增长不受扩散限制的天然火山系统（例如熔岩，穹顶，火成岩，导管填充物）。

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