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

University Of Hawaii, Honolulu

Investigators

Abstract

Hammer EAR-0087463 The 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.