Refinement of the α–β quartz phase boundary based on in situ Raman spectroscopy measurements in hydrothermal diamond‐anvil cell and an evaluated equation of state of pure H2O

Abstract

AbstractIn this study, we determined the α–β quartz phase transition temperatures (Ttrs; up to ~924°C for a total of 23 obtained under 0.1 MPa and elevated pressures) in a hydrothermal diamond‐anvil cell (HDAC) at H2O pressures up to ~1310 MPa by using in situ Raman spectroscopy. When compared with the commonly used α‐quartz Raman band near 465 cm−1 (at 24°C and 0.1 MPa), the one near 128 cm−1 is much more sensitive for detecting Ttr. The corresponding phase transition pressure (Ptr) at each measured Ttr was calculated from three equations of state (EoS) of pure H2O. The corresponding three α–β quartz phase boundaries were compared with those derived from previous experimental results. The best fitted one can be represented by: Ptr (±5.6 MPa) = 0.0008·Ttr2 + 2.8056·Ttr − 1877.5, where 574°C ≤ Ttr ≤ 889°C with R2 = 0.9998. Our results agree, within experimental uncertainties, with most of previous experimental data, and our newly determined α–β quartz Ptr–Ttr phase boundary can be used as a reliable pressure calibrant in HDAC. Furthermore, the experimental procedures used in this study, including the use of Raman spectroscopy criterion for Ttr determination, can be easily applied to obtain improved EoS of geologically important aqueous solutions containing salt(s) at pressure–temperature conditions up to ~1.2 GPa–900°C.