Strength of dry and wet quartz in the low-temperature plasticity regime: insights from nanoindentation

Abstract

Experimental rock deformation has demonstrated that the strength of quartz is significantly reduced by the presence of intracrystalline H 2 O either bonded to the crystal lattice or occurring as micro-fluid inclusions, that is, quartz exhibits hydrolytic weakening (Ave Lallemant & Carter, 1971;Griggs, 1967;Griggs & Blacic, 1965;Tullis & Yund, 1980). Results from laboratory experiments established that hydrolytic weakening occurs in both synthetic and natural quartz crystals with intracrystalline H 2 O contents larger than 20-30 wt ppm (about 150 H/10 6 Si; Stünitz et al., 2017 and references therein). Several different microphysical processes have been proposed to explain hydrolytic weakening in quartz: (a) hydrolyzation of Si-O-Si bonds around dislocations, consequently decreasing the resistance to dislocation motion (i.e., reducing the Peierls stress; Griggs, 1967), (b) enhanced dislocation generation around H 2 O clusters within the crystal lattice (McLaren et al., 1989;Stünitz et al., 2017), and (c) enhanced recovery through increased ionic diffusivities and faster dislocation climb (Post et al., 1996;Tullis & Yund, 1989). Hydrolytic weakening has been experimentally observed in natural and synthetic quartz deformed at high homologous temperature, conditions for which dislocation climb and recovery processes control the overall strain rate (

Viscoplastic Rheology of α‐Quartz Investigated by Nanoindentation

“…Evans (1984) performed microindentation tests on quartz parallel to [0001] over a temperature range of 283ºC to 746ºC and measured hardnesses of 5-13 GPa. A recent study by Ceccato et al, 2021 (in review) also observes room-temperature hardnesses on the order of 8-13.5 GPa. Our results show higher indentation hardnesses at the relevant temperatures when compared to the experiments of Evans (1984), Goldsby et al (2004), andCeccato et al, 2021 (in review), possibly due to the lower maximum load, smaller scale of deformation, or differences in the density of pre-existing crystallographic defects.…”