Orientation selective grain sublimation-deposition in snow under temperature gradient metamorphism observed with diffraction contrast tomography

Abstract

In this study on temperature gradient metamorphism in snow, we investigate the hypothesis that there exists a favourable crystalline orientation relative to the temperature gradient, giving rise to a faster formation of crystallographic facets. We applied in situ time-lapse diffraction contrast tomography on a snow sample with a density of 476kgm-3 subject to a temperature gradient of 52°Cm-1 at mean temperatures in the range between -4.1 and -2.1°C for 3d. The orientations of about 900 grains along with their microstructural evolution are followed over time. Faceted crystals appear during the evolution, and from the analysis of the material fluxes, we observe higher sublimation-deposition rates for grains with their c axis in the horizontal plane at the beginning of the metamorphism. This remains the case up to the end of the experiment for what concerns sublimation while the differences vanish for deposition. The latter observation is explained in terms of geometrical interactions between grains.