Kinematics in Magmatic Rocks with Special Reference to Gabbros

The orientation of particles in suspension flow and the kinematicanalysis of magmatic rocks are illustrated by flow structuresin layered gabbros from the Skaergaard intrusion and the Omanophiolite. In homogeneous flow by simple shear, the shape-preferredorientation of particles tends to become parallel to the flowplane at large strain. Shear criteria are given by tiling, obliquitiesbetween particles of different aspect ratios, and obliquitiesbetween these structures and passive markers (enclaves). Heterogeneousflow with flow partitioning (S/C, shear bands) and vorticity(folds, rotated enclaves) produces spectacular magmatic structuresin layered gabbros, mimicking solid-state structures in metamorphicrocks; they give shear-sense indications concordant with homogeneousflow markers, but are much easier to use. The strong layeringin these gabbros, which is itself flow related, tends to channelthe flow and can often be used as a flow-plane indicator.