Kinetics of pressure-induced effects in water ice/rock granular mixtures and application to the physics of the icy satellites

This paper concerns the rheological experiments on compaction of water ice and water ice/rock samples prepared from granular material. The rock to total mass ratio was C = 0, 0.25, 0.465, 0.5, 1 for five different samples. The temperature was kept constant, T = 213 K, for all experimental runs. The pressure regime, p = 80–820 MPa, is that which is interesting from the point of view of the physics and evolution of the interiors of the icy satellites of the giant planets. The densification rate, (dp/dt)/p, encountered in the experiments decreased from some 10−4s−1 at the beginning of a run to (10⁻⁷–10⁻⁸)s⁻¹ at the end, some hours later. The densification rate itself mainly represents: (I) the rate of decrease of porosity (dq/dt)/q, when the pressure is relatively low (lower than the phase transition pressure ice I ⇒ ice II, approximately 200 Mpa), and (ii) the kinetics of the phase transitions ice I ⇒ ice II ⇒ ice VI when the pressure exceeds 200 and 600 MPa, respectively. The appropriate formulae were fitted to the experimental data: (i) the formula for the rate of decrease of porosity; it is of the same type as it was established previously for pressure up to 17.7 Mpa (Leliwa-Kopystyński and Maeno. J. Glaciology39, 645–655, 1993); (ii) the formula for the phase transition rate. The experimental results, when extrapolated to lower temperatures, provide date appropriate for the icy/rocky regolith of satellites; it is very plausible that the porous regolith layer extended in the past or it extends even now, to the deep interiors of medium size satellites (Kossacki and Leliwa-Kopystyński, Planet. Space Sci.41, 729–741, 1993). The kinetics of the phase transitions within the icy component of satellites must influence the convection and differentiation processes and therefore it is related to the tectonics of satellites.