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Master of Science




Dazhi Jiang


Shape fabrics in high-strain zones are commonly used to constrain deformation processes in the lithosphere. Linear fabric, as a type of shape fabric, usually indicates constrictional strain and is an important feature in orogenic belts. Among all kinds of linear fabrics, the isolated L-tectonites, which are surrounded by strong planar fabrics, are poorly understood. The isolated L-tectonites are generally developed in heterogeneous high-strain zones. Their formation involves heterogeneous and multiscale deformation processes that current single-scale kinematic models cannot explain. To relate isolated L-tectonites in a high-strain zone with its boundary conditions, I apply a multiscale approach. Isolated L-tectonites are regarded as ellipsoidal heterogeneous domains embedded in a high-strain zone. Eshelby’s formalism extended for power-law viscous materials is used to investigate the strain patterns of the partitioned flows in heterogeneous domains. It is shown that, under an imposed flattening or plane-strain deformation field at the high-strain zone scale, L-tectonites can be developed in strong domains regardless of initial shapes or orientations of the strong domains. The numerical modeling is applied to Archean greenstone belts where isolated L-tectonites are developed. The fabric set in greenstone belts has been interpreted by the gravitational sinking of greenstone rocks into the underlying granitoids. The simulations of deformation fields on different scales show that the fabric set can be well explained by transpression. The numerical modeling reproduces field-observed fabrics in greenstone belts that have remained unexplained by current kinematic models.

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