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

In this study, we determined the alpha-beta quartz phase transition temperatures (T(tr)s; up to similar to 924 degrees 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 similar to 1310 MPa by using in situ Raman spectroscopy. When compared with the commonly used alpha-quartz Raman band near 465 cm(-1 )(at 24 degrees C and 0.1 MPa), the one near 128 cm(-1) is much more sensitive for detecting T-tr. The corresponding phase transition pressure (P-tr) at each measured T-tr was calculated from three equations of state (EoS) of pure H2O. The corresponding three alpha-beta quartz phase boundaries were compared with those derived from previous experimental results. The best fitted one can be represented by: P-tr (+/- 5.6 MPa) = 0.0008.T-tr(2) + 2.8056.T-tr - 1877.5, where 574 degrees C <= (tr) <= 889 degrees C with R-2 = 0.9998. Our results agree, within experimental uncertainties, with most of previous experimental data, and our newly determined alpha-beta quartz P-tr-T-tr 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 T-tr determination, can be easily applied to obtain improved EoS of geologically important aqueous solutions containing salt(s) at pressure-temperature conditions up to similar to 1.2 GPa-900 degrees C.

Automated summary

In this study, the alpha-beta quartz phase transition temperatures were determined using in situ Raman spectroscopy at different pressures. The results showed that the Raman peak near 128 cm(-1) is more sensitive for detecting the phase transition. The corresponding phase transition pressure was calculated using three equations of state. The experimental results agree with previous data and can be used as a reliable pressure calibrant in HDAC.