High‐Pressure Transformations and Stability of Ferromagnesite in the Earth's Mantle

et al. 2021

American Mineralogist

Knowledge of the stability of carbonate minerals at high pressure is essential to better understand carbon cycle deep inside the Earth. The evolution of Raman modes of carbonates with increasing pressure can straightforwardly illustrate lattice softening and stiffening. Here, we reported Raman modes of natural magnesite MgCO 3 up to 75 GPa at room temperature using helium as a pressure-transmitting medium (PTM). Our Raman spectra of MgCO 3 showed the splitting of T and ν 4 modes initiates at approximate 30 and 50 GPa, respectively, which could be associated with its lattice distortions The MgCO 3 structure was referred to as MgCO 3-Ⅰb at 30-50 GPa and as MgCO 3-Ⅰc at 50-75 GPa. Intriguingly, at 75.4 GPa some new vibrational signatures appeared around 250-350 and ~800 cm-1. The emergence of those Raman bands in MgCO 3 under relatively hydrostatic conditions is consistent with the onset pressure of structural transition to MgCO 3-Ⅱ reported by theoretical predictions and high pressure-temperature experiments. This study suggests that hydrostatic conditions may significantly affect the structural evolution of MgCO 3 with increasing pressure, which shall be considered for modeling the carbon cycle in the Earth's lower mantle.

Section: Discussionmentioning

confidence: 52%

Section: Discussionmentioning

confidence: 54%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Raman signatures of the distortion and stability of MgCO3 to 75 GPa

et al. 2021

American Mineralogist

“…Carbon mainly exists as accessory minerals (e.g., carbonates, diamond, graphite, and carbides) in the deep mantle due to its relatively low solubility in silicates [1]. Carbonates are considered to be one of the most important carbon carriers from the crust to deep mantle [2][3][4]. Given carbonate inclusions in ultra-deep diamonds originating from the deep mantle, carbonates can descend to the Earth's deep interior [5,6].…”

Section: Introductionmentioning

confidence: 99%

Phase Stability and Vibrational Properties of Iron-Bearing Carbonates at High Pressure

Gui

et al. 2020

Minerals

The spin transition of iron can greatly affect the stability and various physical properties of iron-bearing carbonates at high pressure. Here, we reported laser Raman measurements on iron-bearing dolomite and siderite at high pressure and room temperature. Raman modes of siderite FeCO3 were investigated up to 75 GPa in the helium (He) pressure medium and up to 82 GPa in the NaCl pressure medium, respectively. We found that the electronic spin-paring transition of iron in siderite occurred sharply at 42–44 GPa, consistent with that in the neon (Ne) pressure medium in our previous study. This indicated that the improved hydrostaticity from Ne to He had minimal effects on the spin transition pressure. Remarkably, the spin crossover of siderite was broadened to 38–48 GPa in the NaCl pressure medium, due to the large deviatoric stress in the sample chamber. In addition, Raman modes of iron-bearing dolomite Ca1.02Mg0.76Fe0.20Mn0.02(CO3)2 were explored up to 58 GPa by using argon as a pressure medium. The sample underwent phase transitions from dolomite-Ⅰ to -Ⅰb phase at ~8 GPa, and then to -Ⅱ at ~15 and -Ⅲb phase at 36 GPa, while no spin transition was observed in iron-bearing dolomite up to 58 GPa. The incorporation of FeCO3 by 20 mol% appeared to marginally decrease the onset pressures of the three phase transitions aforementioned for pure dolomite. At 55–58 GPa, the ν1 mode shifted to a lower frequency at ~1186 cm−1, which was likely associated with the 3 + 1 coordination in dolomite-Ⅲb. These results shed new insights into the nature of iron-bearing carbonates at high pressure.

“…http://www.minsocam.org/ (Martirosyan et al, 2021;. The distorted structural environments provide a potential way to transport carbon into the deep mantle through a plethora of high-pressure polymorphisms of carbonate minerals due to diverse bonding patterns for carbon (Boulard et al, 2020;Lobanov and Goncharov, 2020). Meanwhile, these crystallographic characteristics of carbonates likely play an important role in the storage or transportation of incompatible elements (e.g., K, Ba, Sr) and trace elements (e.g., Zn, Co, Ni, Cd) in the deep mantle, as evidenced by syngenetic diamond inclusions and high temperature and high pressure experiment simulation (Farsang et al, 2021b(Farsang et al, , 2021cFrezzotti et al, 2011;Logvinova et al, 2008Logvinova et al, , 2011.…”

Section: Discussionmentioning

confidence: 99%

Effects of hydrostaticity and Mn-substitution on dolomite stability at high pressure

Wang

et al. 2022

American Mineralogist

Studying the structural evolution of the dolomite group at high pressure is crucial for constraining the deep carbon cycle and mantle dynamics. Here we collected high-pressure laser Raman spectra of natural Mg-dolomite CaMg(CO 3 ) 2 and Mn-dolomite kutnohorite Ca 1.11 Mn 0.89 (CO 3 ) 2 samples up to 56 GPa at room temperature in a diamond anvil cell (DAC) using helium and neon as a pressure-transmitting medium (PTM), respectively. Using helium or neon can ensure samples stay under relatively hydrostatic conditions over the investigated pressure range, resembling the hydrostatic conditions of the deep mantle. Phase transitions in CaMg(CO 3 ) 2 were observed at 36.1(25) GPa in helium and 35.2(10) GPa in neon PTM for dolomite-II to -III, respectively. Moreover, the onset pressure of Mn-dolomite Ca 1.11 Mn 0.89 (CO 3 ) 2 -Ⅲ occurs at 23−25 GPa, about 10 GPa lower than that of Mg-dolomite-III, suggesting that cation substitution could significantly change the onset pressure of the phase This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.