Constraints on the Crystallization of Degassing Magmas: An Experimental Study of Crystal Nucleation and Growth Kinetics

火山喷发的风格在很大程度上取决于当上升的岩浆到达浅层时，挥发性成分与熔体的溶解和物理分离的能力。研究深部储层向管道输送岩浆的速率、同喷发脱气和岩浆排出速率之间的相互关系，对于认识喷发方式的控制作用具有重要意义。脱气使饱和水的硅酸盐熔体结晶，这一过程的结果可以被火山学家用来更好地了解岩浆脱气的历史。为了利用天然火山产物的基质晶体结构来解释压力-时间路径，我们需要了解在这种情况下晶体成核和生长的动力学，这是本提案的重点。我们建议关注结晶动力学在地质和火山学意义的多组分系统中的有趣方面。我们将研究合成玻璃和天然玻璃的成核，以分离不同因素（如结晶相的种子和少量的非化学计量氧化物）对天然熔体非均相成核的影响。表面能和熔体粘度对成核速率的相对重要性将在快速减压实验中使用成分作为变量进行检验。该项目的目标是量化长石的成核和生长动力学，这是由于成分（而不是热）过饱和，将结果与现有的理论进行比较，并建立与火山过程相关的一系列压力-时间路径的晶体结构发育模型。

HammerEAR-0087463The styles of volcanic eruptions are determined in large part by the ability of volatile components to exsolve and physically separate from the melt when the ascending magma reaches shallow levels. Study of the interrelationships between magma supply rate to the conduit from deep-seated reservoirs, syn-eruptive degassing, and magma discharge rate at the vent is critical to our understanding of controls on eruptive style. Degassing causes H2O-saturated silicate melts to crystallize, and the results of this process may be exploited by volcanologists for greater understanding of magmatic degassing history. In order to interpret pressure-time paths using the groundmass crystal textures of natural volcanic products, we need to understand the kinetics of crystal nucleation and growth under such circumstances, and that is the focus of this proposal. We propose to focus on the intriguing aspects of crystallization kinetics in a multicomponent system of geologic and volcanological significance. We will study nucleation in synthetic and natural glasses to isolate the effects of different factors (such as seeds of the crystallizing phase and minor amounts of nonstoichiometric oxides) on heterogeneous nucleation in natural melts. The relative importance of surface energy and melt viscosity for nucleation rate will be examined using composition as a variable in rapid decompression experiments. The goal of this project is to quantify feldspar nucleation and growth kinetics due to compositional (rather than thermal) supersaturation, compare the results to available theories, and develop models of crystal texture development over a range of pressure-time paths relevant to volcanic processes.