Fig. 3: Phase diagram section for a representative granulite from Holsnøy.
From: Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening
The phase diagram section has been calculated via Gibbs-free energy minimization by assuming a fixed amount of H2O (see Methods for more details). A Equilibrium mineral assemblages for the granulite from Holsnøy (mineral abbreviations: Cpx: clinopyroxene, Grt: garnet, Ky: Kyanite, Zo: zoisite, cAmph: clinoamphibole, Pl: plagioclase feldspar, Qz: quartz, Pa: paragonite mica, H2O: pure H2O fluid). B The black solid line shows the amount of H2O needed for water-saturation, i.e. fluid-present conditions (the assumed temperature conditions (650 °C) are indicated by dashed line in (A). The red line indicates the amount of H2O (LOI) that was also used for the calculation of the pressure-temperature section (shown in A). The intersection and relative positions of the black and red lines in (B) shows that the H2O content is sufficient to saturate the system only in a pressure range below ~1.0 GPa. For the pressure range between 1–2 GPa, the rock is H2O-undersaturated and no free H2O phase is stable.
