Extrinsic Anisotropy of Two-Phase Newtonian Aggregates: Fabric Characterization and Parameterization

Area of Science:

• Geophysics
• Materials Science
• Tectonics

Background:

• Earth's crust and mantle rocks exhibit mechanical anisotropy due to mineral contrasts.
• This extrinsic anisotropy influences geodynamic processes but is difficult to model at large scales.
• Understanding rock fabric evolution is key to predicting large-scale geological behaviors.

Purpose of the Study:

• To develop a method for indirectly approximating extrinsic viscous anisotropy in two-phase rock aggregates.
• To investigate the impact of varying inclusion properties on rock strength and fabric development.
• To link grain-scale fabric evolution to bulk deformation and material properties.

Main Methods:

• Combined 3D mechanical models of rock fabrics with analytical effective medium theories.
• Simulated two-phase aggregates as rheological approximations of Earth's rocks.
• Parameterized grain-scale fabrics based on bulk deformation and material phase properties.

Main Results:

• Weak inclusions create interconnected weak layers, causing structural weakening of 30-60%.
• Strong inclusions have minimal impact on aggregate strength; lineated fabrics form only at low viscosity contrasts.
• Clogging of rigid inclusions can increase aggregate viscosity beyond theoretical limits.

Conclusions:

• The proposed method effectively approximates extrinsic viscous anisotropy in rocks.
• Inclusion properties and their connectivity critically control rock weakening and fabric development.
• This approach aids in understanding large-scale geodynamic processes influenced by rock rheology.