Textural Evolution of Metemorphic Rocks due to Ostwald Ripening.

This paper presents textural evolution of metamorphic rocks due to Ostwald ripening. First, Crystal size distributions (CSDs) of garnets in various metamorphic rocks are compared with the LSW (Lifshitz-Slyozov-Wagner) distribution for Ostwald ripening. There are two types of CSD. One is consistent with LSW distribution, the other is wider than LSW distribution. The former one has a homogeneous spatial disposition of garnets, and represents the progress of Ostwald ripening. That CSD of the latter type is wider than LSW, is either; 1) because duration of Ostwald ripening is not sufficient, or 2) because spatial disposition of garnets is not homogeneous. LSW theory needs homogeneous spatial disposition of precipitated phase. Ostwald ripening in spatially heterogeneous system is researched by numerical simulation. The results suggest that heterogeneous structure, such as layered structure, are developed by Ostwald ripening. Shape of size distribution is important in two reasons; l) material transport between layers by Ostwald ripening can be evaluated by comparisons of size distributions between layers, and 2) the width of initial size distribution strongly influences an evolution of layering structure.