Compression and simple shear of test models with rigid and deformable inclusions

Abstract

From experimental deformation of test models containing rigid or deformable inclusions embedded in elastic and viscous materials, an attempt has been made to determine the nature of strain in the matrix in relation to deformation or rigid rotation of the inclusions. The experiments indicate that swerving of schistosity around pebbles (a "concordant" relation) is a sure indicator of contrast in competence between pebble and matrix. The commonly recorded rough parallelism (or concordance) between schistosity and deformed pebbles usually develops from the following combinations of conditions, viz., (1) at least a moderate amount of deformation; (2) significant contrast in competence between pebble and matrix; and (3) fairly close spacing among pebbles. Theoretical calculations suggest that development of tapering pressure-shadow zones parallel to schistosity at opposite sides of garnet crystals can be explained by distribution of stress-pressure (average of stress components) around the porphyroblasts. Symmetrical S-shaped si in garnet can give only a range of values of paracrystalline rotation. The actual values within this range can be obtained only if the shear-strain prior to crystallization of garnet is known.