Experimental Study of Bubble Size Distribution in Rhyolitic and Phonolitic Melts: Implications for Vesicle Size Distribution in Pumice

为了确定来自淬火浮石碎屑的结构信息告诉我们关于爆炸喷发期间岩浆脱气过程的信息，了解岩浆上升过程中气泡尺寸分布（BSD）的演变是至关重要的。过程，如聚结，奥斯特瓦尔德熟化，在熔体中的浓度梯度的影响，和多个成核事件都是可能的方式，通过这些方式，最初均匀的气泡尺寸分布来自一个单一的成核事件可能演变成多峰分布更像观察到的浮石碎屑。我们建议在这里实验量化的速率和条件下，这些过程影响BSD的流纹岩和响岩熔体减压速率，压力，温度和水含量适用于岩浆上升之前的碎片限制。我们的研究将通过比较天然高硅流纹岩和响岩组合物（h ~109和105分别）的结果，解决熔体粘度在浮石囊泡尺寸分布的生产中发挥的作用。我们的目标是使用这些实验来约束在适用条件下的预破碎效应，以便更好地约束如何BSD修改可能会发生在喷发过程中产生的VSD的存在淬火浮石。我们的目标，这项工作是一个实验约束模型的BSD的在上升的岩浆破碎之前的演变，并提供更好的限制的过程，有助于在浮石中观察到的囊泡大小分布。

Faust LarsenEAR-0074127It is critical to understand the evolution of bubble size distributions (BSD) during magmatic ascent in order to determine what the textural information from quenched pumice clasts tells us about the processes of magmatic degassing during explosive eruptions. Processes such as coalescence, Ostwald ripening, the effects of concentration gradients in the melt, and multiple nucleation events are all possible ways by which an initially uniform bubble size distribution derived from a single nucleation event may evolve into polymodal distributions more like that observed in pumice clasts. We propose here to experimentally quantify the rates and conditions under which these processes affect BSD's in rhyolitic and phonolitic melts at decompression rates, pressures, temperatures, and water contents applicable to magmatic ascent prior to the fragmentation limit. Our study will address the role that melt viscosity plays in the production of pumice vesicle size distributions by comparing results for natural high-silica rhyolite and phonolite compositions (h ~109 and 105 respectively). Our goal is to use these experiments to constrain pre-fragmentation effects at applicable conditions in order to better constrain how BSD modification may occur during eruptions to produce the VSD's present in quenched pumice. Our goal for this proposed work is an experimentally constrained model of the evolution of BSD's in ascending magma prior to fragmentation, and provide better constraints on the processes that contribute to vesicle size distributions observed in pumice.