Figure 4

Model of fluid transfer induced by differential creep cavitation. (a) Changing size of strain-induced micro-cavities as a function of strain rate. Depending on the balance between strain rate and efficiency of “healing” processes, here represented by the nucleation and growth of a new phase, grain boundary sliding (GBS) is proposed to produce transient cavities with different sizes. While small water-filled cavities occur at low strain rate, larger pores are expected at high strain rate because of constant pressure and temperature that limit the growth rate of new phases in closing cavities. γ₁, γ₂ and γ₃ represent three steps of finite shear strain. (b) Fluid transfer induced by differential creep cavitation across a ductile shear zone. Because of increasing strain rate, creep cavitation produces pores that gradually enlarge from the low- to high-strain zones. More cavities may be also expected for a higher contribution of GBS to deformation because of grain size reduction (not shown here). Fluids are consequently drawn and pumped towards the core of the shear zone until steady-state strain localization is achieved. The fluid gradient is then preserved as long as differential creep cavitation is effective, giving rise to a gradient of fluid content per unit of grain boundary with increasing strain rate (graph). The colour coding mimics the H₂O distribution shown in Fig. 1 from yellow to light blue. Ol = olivine.