The equilibrium boundary of the reaction Mg3Al2Si3O12 + 3CO2 = Al2SiO5 + 2SiO2 + 3MgCO3 at 3–6 GPa

Abstract

The stability of CO 2 fluid in the Earth's mantle is restricted by the carbonation of rockforming minerals. Among those, the reaction with garnet is of particular interest because it constrains the stability of CO 2 fluid in eclogites, whose minerals have been found in the CO 2 -bearing diamonds. In this work, we determined the equilibrium boundary for the reaction Mg 3 Al 2 Si 3 O 12 (Prp) + 3CO 2 (F) = Al 2 SiO 5 (Ky) + 2SiO 2 (Coe/Qz) + 3MgCO 3 (Mgs) over the pressure interval 3-6 GPa using a multianvil press. Owing to the slow kinetics, the reaction was studied in both forward (left to right) and reverse (right to left) directions in experiments with durations extending up to 260 h. Our newly determined boundary is situated 3 GPa / 950±50 °C, 4.5 GPa / 1075±25 °C, and 6 GPa / 1250±50 °C and has the equation P(GPa) = 0.0099×T (°C) + 6.3165. The boundary crosses the 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.

Experimental Modeling of Decarbonation Reactions, Resulting in the Formation of CO2 Fluid and Garnets of Model Carbonated Eclogites under Lithospheric Mantle P,T-Parameters

“…It should be noted that in previous works on the experimental modeling of decarbonation reactions with the formation of garnet by R. Knohe et al [42] as well as Yu. Vinogradova et al [68,69], either buffering was not used, or details made from boron nitride were present in the assembly of the experimental setup. Both the uncontrolled diffusion of hydrogen in the absence of buffering and the presence of BN parts reduce the oxygen fugacity in the high pressure cell (Figure 4), and thus, despite all the care taken in the preparation of these experiments, the reliability of the results obtained is rather controversial.…”

“…Later, we carried out systematic experimental studies to determine the position of decarbonation lines in the P,T field, and established the stability regions of the CO2-fluid in association with pyrope, pyrope-almandine, pyrope-grossular, pyrope-almandine-grossular, and spessartine (Figures 1b and 2, reactions ( 12)- (16) in Supplementary Materials) [64][65][66][67]. These experimental works were continued in studies [68,69].…”

Stability of CO2 Fluid in Eclogitic Mantle Lithosphere: Thermodynamic Calculations

“…Meanwhile, some diamonds that entrapped solid CO 2 at higher pressures may have formed under different conditions-such as based on the redox freezing mechanism [22]. Experiments show that the stability field of CO 2 fluid with minerals of the eclogitic suite in the pyrope-CO 2 and diopside-CO 2 systems extends to higher pressures compared to the peridotite mantle but still does not reach the diamond stability field [23][24][25][26][27]. Nevertheless, the studied systems do not adequately model the compositions of eclogite garnets and clinopyroxenes, which are known to be represented by pyrope-almandine-grossular solid solutions and omphacite (diopside-jadeite solid solution), respectively.…”