In-situ investigation of the vibrational properties of H2O–CO2-bearing and dry K-rich basaltic glasses at high pressure by mid infrared spectroscopy

The vibrational properties of CO2–H2O-bearing and dry synthetic K-rich basaltic glasses were investigated at room temperature and pressures between 0.0001–5.5 GPa using the diamond anvil cell combined with in-situ reflectance and transmittance Fourier Transform infrared micro-spectroscopy. The absorption coefficient calculated from the Kramers-Kronig relation shows that glasses are dominated by the Q2 aluminosilicate unit followed by Q1, Q3. The variation in Qn concentration upon compression suggests that glasses undergo polymerization from ambient pressure to 2 GPa followed by less marked structural changes up to 4 GPa, above which the structure is further polymerized. Once decompressed, glasses retained a polymerized structure. Our results show that 1.03 wt% CO2-1.42 wt% H2O in a glass with 3.10 wt% K2O and 46.77 wt% SiO2 prevent the formation of fully polymerized connections when cold-compressed. Our results can be used to explain the effect of volatiles and alkali on the rheology of natural basaltic magmas.