[1oral308-11] T1.［Topic Session］Metamorphic rocks and tectonics

[T1-O-4] Seismo - Crystal Diagram in Shear Crack Jog of the Plate Boundary Metamorphic Rocks

*mitsuhiro TORIUMI¹ (1. Japan Agency for Marine Earth Science and Tecnology )

Keywords:shear crack jog, plate boundary metamorphic rocks, crystal shape in jog

Sealed shear cracks associate abundant jog filled with albite, quartz, chlorite and calcite in the low - grade metamorphic rocks of the plate boundary. These shear crack jog should open at the time of shear crack growth and propagation, of which the shear slip velocity varies in the very wide range from km to nm order per second, suggesting that the volume increasing rate of the jog may become imbalance with the fluid influx from the surrounding matrix. The simulation of the fluid pressure in jog for various slip velocity can be carried out by means of the equation of state and inflow of aqueous fluid in the increasing jog volume controlled by the slip velocity. The results indicate the various patterns of rapid drop of fluid pressure depending on the shear slip velocity before jog collapse. The change in the degree of oversaturation of albite and quartz is inferred by the difference of fluid pressure in jog and matrix, because of saturation equilibrium of them with matrix aqueous fluid. Therefore, it is possible that the crystal shape of albite and quartz in jog is controlled by the degree of oversaturation controlled by the shear slip velocity, that means the speed of the shear crack slip motion. In the case of the fast earthquakes, the degree of oversaturation reaches over unity, and thus the crystal shape may be dendritic, but in the medium speed slip, it should be flower-like shape, and in the very slow slip event, it may be euhedral shape. The diagram of slip velocity and temperature is divided into the regimes of dendrite, flower, acicular (needle), and euhedral shape.