Evolution of H2O content in deforming quartz aggregates: An experimental study

Abstract

Deformation experiments were carried out on pure quartzite samples (>99% quartz) with a grain size of ∼200 μm from Tana, Northern Norway. Deformation conditions were 900 °C, 0.1 wt% H2O added, strain rate ∼1 × 10−6 s−1 at variable confining pressures from 600 to 2000 MPa. Detailed FTIR measurements of H2O indicate that the H2O content in the grain boundary region is higher than that inside quartz grains. Hydrostatic treatment and deformation at the chosen temperature and pressure conditions lead to further H2O loss from grain interiors and H2O increase in the grain boundary region. Varying the confining pressure does not have an observable effect on the H2O transfer from grains to the grain boundary region. The 3585 cm−1 absorption band increases systematically with increasing confining pressure. As this band is associated with OH in dislocations, the increase may indicate an increased dislocation density with increasing pressure. The triplet of 3317, 3375 and 3438 cm−1 associated with Al-content in quartz increases in the grain boundary region indicating an exchange of H+ together with Al3+ for Si4+. The Al and H exchange suggest dissolution-precipitation processes in the grain boundary region facilitating the movement of the quartz grain boundaries (grain boundary migration). The H2O in the grain boundary region will be important for enhancing grain boundary migration and thus recrystallization processes during deformation.