Abstract
Abstract. In experiments designed to understand deep shear zones, we show that periodic porous sheets emerge spontaneously during viscous creep and that they facilitate mass transfer. These findings challenge conventional expectations of how viscosity in solid rocks operates and provide quantitative data in favour of an alternative paradigm, that of the dynamic granular fluid pump model. On this basis, we argue that our results warrant a reappraisal of the community's perception of how viscous deformation in rocks proceeds with time and suggest that the general model for deep shear zones should be updated to include creep cavitation. Through our discussion we highlight how the integration of creep cavitation, and its Generalised Thermodynamic paradigm, would be consequential for a range of important solid Earth topics that involve viscosity in Earth materials like, for example, slow earthquakes.
Highlights
Our existing models for mantle convection, the advance of glaciers and even the dynamics of the seismic cycle all include, and rely on, the concept that solids can be viscous and flow with time
We claim this because our results show that a mylonitic shear zone deforming viscously can spontaneously develop highly anisotropic and periodic porous domains
Our results validate the prediction of pore sheets in the dynamic granular fluid pump model (Fusseis et al, 2009) and extend it to show that pore sheets can develop spontaneously in homogenous rocks, with a periodic and oriented character
Summary
Our existing models for mantle convection, the advance of glaciers and even the dynamics of the seismic cycle all include, and rely on, the concept that solids can be viscous and flow with time. The accepted conceptual model for lithospheric shear zones supposes that there is a mechanical stratification with depth from an upper frictional to lower viscous domain (Sibson, 1977; Schmid and Handy, 1991; Handy et al, 2007) In this model, viscous creep is a continuous slow background deformation and, at certain conditions, is punctuated by fracturing. Thermodynamic model (cf Hobbs et al, 2011) known as the dynamic granular fluid pump (Fusseis et al, 2009) While much of this paradigm remains to be tested, the notion that mylonites generate self-sustaining and dynamic pathways for mass transport is radical and consequential for the interpretation of how deep shear zones behave during deformation. A key consequence of this would be that the energetics of the deforming system become the keystone of our perspective rather than the mechanics
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