Post-failure deformation mode switching in volcanic rock.

Area of Science:

• Geophysics
• Rock Mechanics
• Material Science

Background:

• Porous rocks exhibit dilatant or compactant inelastic deformation beyond a threshold compressive stress.
• Understanding physical property responses to deformation is crucial for crustal mass and heat transport, and pressure evolution.
• Transitions between dilatancy and compaction (failure modes) are observed but understudied.

Purpose of the Study:

• To investigate complex post-failure deformation behavior in porous rocks.
• To elucidate the mechanisms driving transitions between compaction and dilation.
• To understand the impact of these transitions on rock physical properties.

Main Methods:

• Performed targeted mechanical deformation experiments on porous andesites.
• Investigated a sample suite and effective pressure range straddling positive and negative volumetric responses to compression.
• Analyzed changes in physical properties, particularly permeability, following deformation.

Main Results:

• Identified two post-failure critical stress states: compaction-to-dilation and dilation-to-compaction transitions.
• Demonstrated that multiple deformation mode switches can occur under shallow crustal conditions.
• Observed a two-order-of-magnitude increase in permeability for samples undergoing dilatant-to-compactant failure, despite minor volumetric change.

Conclusions:

• Post-failure deformation mode switching is significant in shallow crustal settings.
• Dilatant-to-compactant failure mode switching dramatically enhances permeability, impacting solute and heat transfer.
• These phenomena are critical for understanding fluid pressure evolution in volcanic environments.