We performed a systematic investigation of mechanical compaction, strain localization, and permeability in Leitha limestone. This carbonate from the area of Vienna (Austria) occurs with a broad range of grain sizes and porosity, due to changes in depositional regime and degree of cementation. Our new mechanical data revealed a simple relation between porosity and mechanical strength in both the brittle and ductile regimes. Increasing cementation and decreasing porosity led to a significant increase of the rock strength in both regimes. Micromechanical modeling showed that the dominant micromechanisms of inelastic deformation in Leitha limestone are pore‐emanated microcracking in the brittle regime, and grain crushing and cataclastic pore collapse in the ductile regime. Microstructural analysis and X‐ray computed tomography revealed the development of compaction bands in some of the less cemented samples, while more cemented end‐members failed by cataclastic flow in the compactant regime. In contrast to mechanical strength, permeability of Leitha limestone was not significantly impacted by increasing cementation and decreasing porosity. Our microstructural and tomography data showed that this was essentially due to the existence of a backbone of connected large macropores in all our samples, which also explained the relatively high permeability (in the range of 2–5 darcies) of Leitha limestone in comparison to other carbonates with significant proportion of micropores.
We use the Eshelby solution modified for a viscous fluid to model the evolution of three-dimensional flanking structures in monoclinic shear zones. Shearing of an elliptical crack strongly elongated perpendicular to the flow direction produces a cylindrical flanking structure which is reproducible with 2D plane strain models. In contrast, a circular or even narrow, slit-shaped crack exhibits a reduced magnitude of the velocity jump across the crack and results in smaller offset and a narrower zone of deflection than predicted with 2D-models. Even more significant deviations are observed if the crack axes are oriented at an oblique angle to the principal flow directions, where the velocity jump is oblique to the resolved shear direction and is modified during progressive deformation. The resulting triclinic geometry represents a rare example of triclinic structures developing in monoclinic flow and may be used to estimate the flow kinematics of the shear zone.
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