Melt segregation from highly crystallized magmas under simple shear

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We examined the microstructure of magma under simple shear. The evolution of the microstructure is governed by two factors : (1) geometric relationships between the particle orientation and the maximum principal axis and (2) magnitude of particle-fluid and particle-particle interactions, which modifies the rotation behavior of particles. The first factor results in the coupling of the particle orientation and the local fraction of particles. The second factor controls the rotation behavior of particles. Through the combined effect of the two factors, particles are rearranged because of shear-induced strain, and both the microstructure and the bulk viscosity reach a steady-state condition. Under this condition, the microstructure is composed of two domains having different particle fractions and particle orientations. Increase in particle fraction and particle-particle interaction develops the cluster with strong inter-particle force, which results in the segregation of liquid. These findings have important implications for the kinematics of the flow-related microstructure recorded in igneous rocks.