Decompression concaves of shear crack jog in the plate boundary metamorphic rocks

Abstract

There are abundant shear crack jogs sealed with albite, chlorite, epidote, and quartz in the low-grade basic schists, manifesting jog formation during metamorphism. These shear crack jogs have decompression concaves, that are classified into two types: one is sharp outline type and the other diffusive one. The former displays sharp boundary between albite and quartz sealing jog and chlorite dominant matrix, but the latter does the gradual change of volume ratio of the very fine-grained albite and chlorite from the matrix to the jog interior. It is important that the boundary shape is fitted by sinusoidal curve of the cross-sectional boundary shape, but not concatenated one, thereby suggesting the decompression mechanism of the dent formation. The periodic structure of the concave structure is possibly interpreted by the depression mechanics of the low fluid pressure of jog volume at the time of shear crack motion (growth and propagation). In this talk, the author proposes the kinetics of the decompression dent formation during the plate boundary metamorphism.