Analogue experiments

In situ analogue experiments have revealed that disequilibrium features can simply occur as a result of the combined effect of static liquid distribution with ongoing surface energy driven recrystallization [Walte et al. 2003]. For these analogue experiments a 30-100 µm thin sheet of norcamphor (C2H10O), a hexagonal organic crystal compound [Bons, 1992; Herwegh and Handy, 1996] plus ethanol liquid was placed between two glass slides and observed with a microscope under static conditions (see simulation 7). When surrounded by liquid the norcamphorforms circular crystals without crystal facets, therefore it has an effectively isotropic solid-liquid surface energy. The liquid is distributed within three-grain triple junctions with a mean dihedral angle of 10-15°. The norcamphor–ethanolsystem can therefore be used as an analogue for a low surface energy anisotropy phase plus a well wetting liquid or melt such as quartz plus granitic melt.The film shows that the melt triangles are regular as long as adjacent grains are rather equal sized. However, when a small grain shrinks and disappears, the melt filled triangles are distorted and temporarily form a disequilibrium feature.

The simulation of this experiment (see simulation 8) shows the same behavior of melt pockets.In both the analogue experiment and the simulation, the equilibrium is disturbed as soon as a grain collapses. During the collapse and during the formation of the disequilibrium shaped melt pockets, melt is redistributed and the wetting angles adjust so that the new volume of melt can be accommodated. If the disequilibrium melt pocket splits into two E-shaped melt pockets, melt is again redistributed and the wetting angle readjusts.

Simulation 7. In situ analogue experiments

In situ analogue experiments of a norcamphor plus ethanol aggregate. The aggregate undergoes grain growth and develops the same disequilibrium structures during collapse of small grains that are seen in the numerical experiment. Simulation 8 is a numerical simulation using the same initial microstructure that was used in the analogue experiments.

Simulation 8. In situ analogue experiments

Simulation of the analogue experiment shown in animation 7. The simulation and the analogue experiment show the same behavior of melt pockets. In both the analogue experiment and the simulation, the equilibrium is disturbed as soon as a grain collapses.