High‐pressure Raman study of nyerereite from Oldoinyo Lengai

Abstract

A rare sodium carbonate nyerereite, (Na,K)2Ca(CO3)2, first found in unique natrocarbonatite lava of Oldoinyo Lengai volcano, also attracted a lot of attention as an inclusion phase in mantle minerals formed in the course of deep carbonatite magmatism. We measured the evolution of nyerereite Raman spectra under quasi‐hydrostatic compression up to 6.4 GPa using a diamond anvil cell. The ν4(CO32−) band (710 cm−1 at ambient pressure) and ν1(CO32−) doublet (1077 and 1086 cm−1 at ambient pressure) demonstrated a positive pressure shift with dν/dP irregularities at 0.5 and 3.0 GPa. The obtained calibration was then used for residual pressure measurements in nyerereite‐bearing inclusions in olivine from the Udachnaya‐East kimberlite. Copyright © 2017 John Wiley & Sons, Ltd.

High‐Pressure/Temperature Behavior of the Alkali/Calcium Carbonate Shortite (Na2Ca2(CO3)3): Implications for Carbon Sequestration in Earth's Transition Zone

“…Accordingly, we measured the high‐pressure Raman spectra of nyerereite to pressures of 25 GPa. This complements recent work to 6.4 GPa by Rashchenko et al (). The crystal structure of nyerereite is complex due to the existence of three ambient pressure phases ( α , β , γ ), its incommensurate modulation (Gavryushkin et al, ), and variable elemental concentration (in all natural samples of nyerereite, there is some amount of substitution of sulfur (as SO 4 ), phosphorus (as PO 4 ), and other alkalis or alkaline earths for the sodium or carbonate ions: Gavryushkin et al, ).…”

“…Up to 5 GPa, the mode associated with the in‐plane bend increases in frequency with pressure at 1.33(32) cm −1 GPa −1 ; this shift is similar to the pressure shift of shortite's in plane bend, and with the shift reported by Rashchenko et al () above 3 GPa. The two modes associated with the symmetric stretch also increase in frequency with pressure at 2.89(35) and 3.20(16) cm −1 GPa −1 (Figures S3a and Sb and Table S7), which are slightly lower than the shifts of Rashchenko et al (). Both these shifts are less than that of shortite, indicating that the symmetric stretches in nyerereite are less affected by compression than the carbonate ions in shortite.…”

“…At 5 GPa, the in‐plane bend splits from one peak to three peaks; this splitting persists to the highest pressure, 25 GPa. Rashchenko et al () report a change in pressure dependences of the Raman bands of nyerereite near 3 GPa but do not observe splitting. The three resulting deconvolved in‐plane modes increase in frequency at 1.21(3), 1.80(8), and 2.22(16) cm −1 GPa −1 (Figures S3a and S3b and Table S7).…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…They measured the evolution of nyerereite Raman spectra under quasihydrostatic compression up to 6.4 GPa using a diamond anvil cell. The obtained calibration was then used for residual pressure measurements in nyerereite‐bearing inclusions in olivine from the Udachnaya‐East kimberlite . Rastogi et al described in situ Raman spectroscopic studies of polyvinyl toluene (PVT) under laser‐driven shock compression and comparison with hydrostatic experiments.…”

GeoRaman

“…Behavior of phengitic mica at high‐pressure and ‐temperature conditions, typical for “cold” subduction zone, was analyzed by Goryainov et al. The pressure dependence of Raman bands for alkaline carbonate (nyerereite) was obtained by Rashchenko et al in order to estimate residual pressure values for melt inclusions in olivine from sheared garnet peridotites, one of the deepest mantle xenoliths. In situ high‐pressure Raman spectra were collected on pyroxenes with compositions CaCoSi 2 O 6 , CaMgSi 2 O 6 , CaMgGe 2 O 6 , and CaCoGe 2 O 6 , up to P = 8.3 GPa by Tribaudino et al.…”