The Effects of Deformation on the Early Kinetics of Basaltic Magmas

Crystals and bubbles nucleate and grow in a magma that experiences a range of temperatures, pressures and strain-rates. We have a good conceptual and sometimes quantitative understanding of how crystallization and bubble nucleation are controlled by decompression and cooling. Here we explore the effect of strainrate on the crystallization kinetics of magmas. In order to understand the interaction between deformation and crystallization, samples of basalt were deformed during their crystallization. We made measurements at subliquidus conditions (1160 degrees C) and deformed samples in compression at strain-rates varying from 0 to 2 x 10(-4) s(-1) for a total strain of 0.31. We simultaneously imaged the samples using X-ray microtomography. Without deformation, no crystallization was observed over the course of a 260 min experiment. Once deformation was applied, crystallization initiated. Deformation increased the nucleation rate, increased crystal growth rates, and decreased the incubation time. Increasing the strain-rate, however, does not show a discernable effect of crystallization kinetics. We hypothesize that deformation may have an effect on the parameters that govern the crystallization kinetics of magmas, such as activation energy and diffusion by changing chemical potentials.