Dynamical immiscibility of aqueous carbonate fluid in shortite-water
system at high P-T conditions
Anhydrous carbonate shortite compressed in the aqueous fluid at high P-T
(up to 5 GPa, 350°C) was studied with in situ Raman spectroscopy. The
DFT was used to calculate the lattice dynamics and interpret the
vibrational spectra. The shortite Raman bands are broadening with
pressure and temperature, and signal are decreasing that is caused by
gradual structure amorphisation accompanied by an orientational
disordering of CO$_3$ triangle units. Despite the aqueous medium
presence at high temperature and pressure, shortite did not go hydrated.
At 3.2 GPa and 250°C, shortite begins to dissolve followed by
crystallisation of aragonite and aragonite’ . A remnant part of shortite
crystals was presented in the ex-situ sample. The transition of shortite
to aragonite’ was monitored by in situ Raman spectra in the C-O
stretching range: strong doublet transforms into singlet at
~4 GPa, 250°C. Additionally, the phases X-phase is
characterised by strongest narrow 1358 cm-1 band.
X1- and X2-phases are expected to
represent organic materials are the most believable Na-formate and some
polymorphs of Ca-formate.
The unusual behaviour of aqueous carbonate fluid was observed at 4.8 GPa
and 300-350°C. This process is characterised by the active formation of
micro-bubbles that are inserted one into another. The existence time of
the micro-bubbles is varied within 2-60 seconds. Micro-bubbles are
considered to be a result of the two immiscible fluids stratification.
This unusual dynamical immiscibility of the fluid promotes the
appearance of several crystalline carbonates and organic molecular