’Spin behavior of ordered/disordered ankerite at high pressures

Fe-bearing carbonates are increasingly recognized as key phases for iron and carbon storage in Earth’s deep interior, yet their physical properties at high pressure remain poorly constrained, particularly for compositionally complex and structurally disordered systems. In this study, we investigate the high-pressure behavior of ordered and disordered ankerite, Ca(Mg₁₋ₓFeₓ)(CO₃)₂ (0 ≤ x ≤ 0.7), to assess the influence of cation ordering on structural evolution, elastic properties, and Fe spin behavior[1,2]. The present work investigates the high-pressure (HP) behaviour of ankerite, Ca(Mg_1-xFe_x)(CO₃)₂ (x=0.4, 0.7), crystallizing in the R-3 space group, and disordered ankerite with R-3c symmetry. Cation ordering and disordering influence on the physical properties and phase evolution of Fe-dolomite and ankerite [1,2], with important implications for their elastic behaviour, that might help in partially explaining the observed seismic anisotropic anomalies in the mantle wedge [3] as well as contributing in the carbonate’s detection in the inner Earth [4]. Particular attention is given to comparisions with the single carbonate magnesiosiderite, focusing on the Fe spin behavior at high pressure. The analysed P conditions reach 80 GPa, higher than the range typical of the Fe spin crossover in single carbonate magnesiosiderite, i.e., ~43 GPa at room temperatures [5][6]. The results obtained in this work confirm that neither ordered nor disordered ankerite undergo a high-spin to low-spin transition up to 80 GPa, independently on the Fe content.

 

The project was partially funded by the ‘’BMBF-Verbundprojekt 05K2019-Nanoextrem2” and “DFG core facility for high pressure research” (2018) and “SIMP Research Grant in Crystal ‐ chemistry, in memory of Prof. Fiorenzo Mazzi” (2022).

 

 

References:

[1] Zucchini A et al. (2014) Phys Chem Miner 41(10):783-793

[2] Zucchini A et al. (2017) Eur J Mineral 29:227-238

[3] Liu X and Zhao D (2017) Geophys J Int 210:1410-1431

[4] Chariton S et al (2020) Am Miner 105(3):325-332,

[5] Cerantola V et al. (2017) Nat Commun 8:15960

[6] Liu J et al. (2014) Am Mineral 99:84-93