SHAPE PREFERRED ORIENTATION OF RIGID PARTICLES IN A VISCOUS MATRIX - REEVALUATION TO DETERMINE KINEMATIC PARAMETERS OF DUCTILE DEFORMATION

The development of the shape preferred orientation of rigid elliptical bodies during non-coaxial deformation is theoretically simulated in a two-dimensional Newtonian matrix. The angular velocity of a rigid ell iptical body (phi) can be expressed as phi = V/R(2) + 1[R(2) sin(2) ph i cos Theta + Cos(2) phi Cos Theta - (R(2) - 1) sin(2) phi sin Theta] where phi is the angle between the shear plane and the longest axis of the ellipse, R is the aspect ratio of the ellipse, V is a constant, a nd Theta is the newly introduced index angle to describe degree of non -coaxiality between simple shear and pure shear defined as tan Theta = epsilon/gamma. gamma and epsilon are simple shear strain rate and pur e shear strain rate, respectively. The initial distribution pattern of the elliptical bodies is assumed to be random in an R/phi diagram, ac id a series of the distribution patterns was calculated using the abov e equation with increasing deformation at varying Theta. When deformat ion is simple shear (i.e. Theta = 0 degrees), all elliptical bodies ro tate with various angular velocities, resulting in a skewed distributi on in the R/phi diagram. In contrast, for pure shear (i.e. Theta = 90 degrees) all of them asymptotically settle their longest axes on a pla ne perpendicular to the compression axis, resulting in strongly concen trated and symmetric distribution patterns in the R/phi diagram. When deformation is general noncoaxial (0 degrees < Theta < 90 degrees), di stribution patterns in the R/phi diagram change systematically from th e pattern similar to that of Theta = 0 degrees to that of Theta = 90 d egrees with increasing Theta. These R/phi diagrams can be used for est imating the degree of non-coaxiality. We analyzed shape preferred orie ntation of porphyroclasts in two mylonites, and concluded that deforma tion within the mylonites contain a certain amount of pure shear compo nent that superimposes on a simple shear component.