変成鉱物の粒径分布と空間分布

Abstract

This paper reviews recent progress in analysis of crystal size distributions (CSD) and spatial dispositions of minerals in metamorphic rocks. Mineral growth in metamorphic rocks consists of two stages: the recrytallization stage in which nucleation and growth makes in progress by net transfer reactions and the annealing stage in which Ostwald ripening is operative. Minerals from contact aureoles will preserve the original CSD produced by nucleation and growth because it may suffer little annealing effects. Two distinct CSD patterns, however, has been reported from contact aureoles. One is that by Kretz, which shows nearly log-normal distribution, indicating time-dependent nucleation rate under the assumption of constant growth rate. The other is that by Cashman and Ferry, which shows CSD pattern caused by constant rates of nucleation and growth. Normal or log-normal size distributions of minerals from regional metamorphic terrain has been also an enigma, because such CSD can be produced either by Ostwald ripening, or by diffusion-controlled nucleation and growth. This paper will give an overview for the resolution of these problems.