Organic-Mediated Formation and Spectroscopic Characterization of Fe-Mg Carbonates: Laboratory Insights into Martian Carbonate Mineralogy

The identification of siderite-magnesite solid solutions provides important constraints on habitable environments on Mars. It offers insights into geochemical conditions, such as redox state and the availability of divalent cations, that could support carbonate formation. In this study, a series of pure siderite-magnesite solid solutions were synthesized by the hydrothermal method in the laboratory. ICP-OES was employed to determine the Fe²⁺ and Mg²⁺ contents, thereby confirming the compositions of the synthesized magnesite-siderite solid solutions. X-ray diffraction (XRD) was used to check the purity and homogeneity of synthesized magnesite-siderite solid solutions and help to understand of magnesite-siderite solid solutions in Gale Crater. The Raman spectra of synthesized samples were measured and compared with the Raman spectra measured by SHERLOC and SuperCam Raman at different sites to help the magnesite-siderite solid solutions identified in Jezero Crater. Linear relationships between main Raman peak positions (v1) of carbonate ion (CO_3^(2-)) and mole percent of magnesium ions (Mg#) were established (R2=0.997), and were used to predict the Mg# of magnesite-siderite solid solutions within Jezero crater. In addition, synthesis of siderite-magnesite solid solution was performed under hydrothermal conditions, where reduced organic compounds played a key role in mineral formation, which would provide experimental constraints on the geological and geochemical pathways of carbonate formation on Mars.

菱铁矿-菱镁矿固溶体的识别可为火星宜居环境提供重要约束，可为碳酸盐形成所需的地球化学条件（如氧化还原状态与二价阳离子供给情况）提供认知参考。本研究通过实验室水热法合成了一系列纯菱铁矿-菱镁矿固溶体：采用电感耦合等离子体发射光谱法（ICP-OES）测定样品中二价铁（Fe²⁺）与二价镁（Mg²⁺）的含量，以此确认合成得到的菱镁矿-菱铁矿固溶体的组分；借助X射线衍射（XRD）表征合成样品的纯度与均一性，并辅助解读盖尔撞击坑中的菱镁矿-菱铁矿固溶体。本研究测定了合成样品的拉曼光谱，并与不同采样点由SHERLOC与SuperCam拉曼光谱仪获取的拉曼光谱进行对比，以辅助识别杰泽罗撞击坑中的菱镁矿-菱铁矿固溶体。研究建立了碳酸根离子（CO₃²⁻）的主拉曼峰位（v₁）与镁离子摩尔占比（Mg#）之间的线性关系（决定系数R²=0.997），并利用该关系预测了杰泽罗撞击坑内菱镁矿-菱铁矿固溶体的Mg#值。此外，本研究在水热条件下完成了菱铁矿-菱镁矿固溶体的合成，其中还原态有机化合物在矿物形成过程中发挥关键作用，该结果可为火星碳酸盐形成的地质与地球化学路径提供实验约束。