Goryainov Sergey, Krylov Alexander, Borodina Ulyana, Likhacheva Anna, Krylova Svetlana, Seryotkin Yurii, Bogdanov Nikita, Vtyurin Alexander, Grishina Svetlana
Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, prospect Acad. Koptyug 3, Novosibirsk, 630090, Russia.
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok, 50, bld. 38, Krasnoyarsk, 660036, Russia.
Spectrochim Acta A Mol Biomol Spectrosc. 2024 Dec 5;322:124801. doi: 10.1016/j.saa.2024.124801. Epub 2024 Jul 14.
The study of Na-carbonates stability and their transformations in aqueous carbonate fluid under high P-T conditions is relevant from the point of view of the understanding geochemical processes of the Na-assisted carbon circulation in the Earth's crust and subduction zones. In situ Raman study of Na-bearing carbonate-water-Fe-metal system in diamond anvil cell (DAC) at high P-T conditions revealed that carbonates decompose with abiogenic formation of formates and other organic compounds that differs from behavior of carbonates in dry system. XRD and FTIR methods have been used additionally to determine the phase composition. Na-bearing carbonates (nahcolite NaHCO, shortite NaCa(CO) and cancrinite NaCa[(CO)AlSiO]⋅2HO) in aqueous fluid decompose to form simple carbonates and formates (as dominant organic molecules) at moderate P-T parameters (above ∼0.2 GPa, 200 °C). Our experimental results directly confirm the hypothesis of Horita and Berndt (Science, 1999) about possible yield of organic formates in the carbonate-water-metal system. Nahcolite NaHCO in aqueous fluid in the presence of Fe metal decomposes into anhydrous phases: natrite γ-NaCO, siderite, magnetite (due to dissolution of Fe steel gasket), Na-formate and likely organic molecular crystalline solvate of Na-formate and methyl formate. Shortite decays into anhydrous phases: aragonite CaCO, Na-Ca-formates and an amorphous phase. Cancrinite decomposes to unidentified carbonate-alumonosilicate phases, Na-Ca-formates and unknown organic molecular crystal. Magnetite is also formed in this system due to dissolution of Fe steel gasket used in DAC. The present study provides a new insight in processes of abiogenic formation of organic matter from carbonates in the crust and upper mantle.
从理解地壳和俯冲带中钠辅助碳循环的地球化学过程的角度来看，研究高压高温条件下水溶液中碳酸钠的稳定性及其转变具有重要意义。在金刚石对顶砧（DAC）中对含钠碳酸盐 - 水 - 铁金属体系进行的原位拉曼研究表明，在高压高温条件下，碳酸盐分解并非生物成因地形成甲酸盐和其他有机化合物，这与干燥体系中碳酸盐的行为不同。另外还使用了X射线衍射（XRD）和傅里叶变换红外光谱（FTIR）方法来确定相组成。在中等压力 - 温度参数（高于约0.2吉帕，200℃）下，含钠碳酸盐（天然碱NaHCO₃、碳钠钙石NaCa(CO₃)₂和钙霞石NaCa[(CO₃)₂AlSiO₄]·2H₂O）在水性流体中分解形成简单碳酸盐和甲酸盐（作为主要有机分子）。我们的实验结果直接证实了堀田和伯恩特（《科学》，1999年）关于碳酸盐 - 水 - 金属体系中可能产生有机甲酸盐的假设。在铁金属存在下，水性流体中的天然碱NaHCO₃分解为无水相：亚硝酸钠γ - Na₂CO₃、菱铁矿、磁铁矿（由于铁钢垫片溶解）、甲酸钠以及可能的甲酸钠和甲酸甲酯的有机分子晶体溶剂化物。碳钠钙石分解为无水相：文石CaCO₃、钠 - 钙甲酸盐和非晶相。钙霞石分解为未鉴定的碳酸盐 - 铝硅酸盐相、钠 - 钙甲酸盐和未知的有机分子晶体。由于DAC中使用的铁钢垫片溶解，该体系中也形成了磁铁矿。本研究为地壳和上地幔中碳酸盐非生物成因形成有机物的过程提供了新的见解。
