3:45 PM - 4:00 PM
[SCG45-32] Rheological transitions from stable flow to localized shear in FEM models for a block in matrix texture
Keywords:Rheological heterogeneity, melange, Finite element method modeling
Variable slip behavior along subduction plate interfaces, ranging from slow to fast, have been modeled as being due to rheological heterogeneity. This concept, akin to the asperity patch model, is often thought to be represented by block-in-matrix textures in tectonic mélanges. Previous studies have qualitatively discussed the rheological behavior of mélanges with their geological occurrences, and highlighted ther existence of tensile fractures in sandstone blocks along with shear veins in the matrix, a pattern that suggests different rheological responses under time-varying pressure-temperature (P-T) conditions.
This study employs the LaCoDe finite element code to model the rheology of a 2-D mélange. Here we focus on the interactions between single block and its surrounding matrix. The mechanical behavior of lithospheric rocks is treated using visco-elasto-plastic extensions of the Stokes equations for creeping flow. Two primary deformation states are identified: stable viscous deformation and localized shear deformation. These states are characterized by distinct stress and strain rate distributions.
A phase diagram is presented to illustrate this rheological transition. We find that stable flow tends to occur at slower shear strain rates and smaller matrix viscosities, while localized shear is observed at faster shear strain rates and larger matrix viscosities. The transition zone, characterized by partial localization with minimal stress drop, plays a crucial role in bridging stable viscous deformation and fully localized shear failure. This zone represents a progressive change in mechanical behavior, influenced by velocity boundary conditions, rather than a sharp boundary. It appears that he transition between these states is governed by the shear strain rate and the viscosity contrast between the block and its surrounding matrix. Understanding this intermediate state is essential for accurately predicting deformation modes and their dependence on external parameters.
The study also correlates the characteristics of shear stress and strain rate distributions with deformation textures observed in natural tectonic mélanges. Extensional cracks in sandstone blocks and micro-faults in the matrix can be explained by the competence contrast and stress concentration patterns observed in the numerical models. The findings provide valuable insights into the conditions under which rheological transitions occur, determined by specific physical parameters, and highlight the importance of velocity boundary conditions in controlling deformation modes.
This research enhances our understanding of the rheological behavior of block-in-matrix textures and their implications for slip styles at subduction plate interfaces. It offers a quantitative evaluation of the factors and geometric strain and failure patterns that influence rheological transitions in tectonic mélanges.
This study employs the LaCoDe finite element code to model the rheology of a 2-D mélange. Here we focus on the interactions between single block and its surrounding matrix. The mechanical behavior of lithospheric rocks is treated using visco-elasto-plastic extensions of the Stokes equations for creeping flow. Two primary deformation states are identified: stable viscous deformation and localized shear deformation. These states are characterized by distinct stress and strain rate distributions.
A phase diagram is presented to illustrate this rheological transition. We find that stable flow tends to occur at slower shear strain rates and smaller matrix viscosities, while localized shear is observed at faster shear strain rates and larger matrix viscosities. The transition zone, characterized by partial localization with minimal stress drop, plays a crucial role in bridging stable viscous deformation and fully localized shear failure. This zone represents a progressive change in mechanical behavior, influenced by velocity boundary conditions, rather than a sharp boundary. It appears that he transition between these states is governed by the shear strain rate and the viscosity contrast between the block and its surrounding matrix. Understanding this intermediate state is essential for accurately predicting deformation modes and their dependence on external parameters.
The study also correlates the characteristics of shear stress and strain rate distributions with deformation textures observed in natural tectonic mélanges. Extensional cracks in sandstone blocks and micro-faults in the matrix can be explained by the competence contrast and stress concentration patterns observed in the numerical models. The findings provide valuable insights into the conditions under which rheological transitions occur, determined by specific physical parameters, and highlight the importance of velocity boundary conditions in controlling deformation modes.
This research enhances our understanding of the rheological behavior of block-in-matrix textures and their implications for slip styles at subduction plate interfaces. It offers a quantitative evaluation of the factors and geometric strain and failure patterns that influence rheological transitions in tectonic mélanges.