12:30 PM - 12:45 PM
[SMP46-03] Grain Size Grading of Garnet in the Liesegang Metamorphism
Keywords:grain size, grading, Liesegang, metamorphism
The very puzzling phenomena is that the grain size of metamorphic garnet shows apparently gradational in both basic and politic schists, for bulk chemistries of large grain and small - grain layers are not different with each other and for chemical zonings of large and small grains of garnet display very similar pattern. These facts suggest that the domain structure by diffusion and growth of garnet should be formed in the layer and the spacing of the domain changes gradually across the grain - size layering in the metamorphism. The layering shows parallel to subparallel against the schistosity plane, suggesting the parameter changes uniaxialy along the normal direction against the schistosity. The length scales of the grain size layering ranges from several to several ten cm, being likely to those of the compositional banding derived from metasomatism. Judging from these facts, it seems that the size grading process in the plate boundary metamorphism is governed by the diffusion, reaction and grain growth mechanism, that is the precipitation mechanism in the Liesegang bands. The precipitation in the Liesegang band is considered as the Cahn - Hillert - Cook process (1), which is characterized by the relation of average grain size, size distribution, width of the layer, and spacing distribution among grains. In this paper, we would like to investigate these relations of the size grading of garnet in the subduction zone metamorphism.References(1), A. DEWIT, 1999, Advances in Chemical Physics, Volume109, Edited by I. Prigogine and Stuart A. Rice ISBN 0-471-32920-7 0 1999 John Wiley & Sons, Inc