High-pressure and high-temperature vibrational properties and anharmonicity of carbonate minerals up to 6 GPa and 500 °C by Raman spectroscopy
High-pressure and high-temperature vibrational properties and anharmonicity of carbonate minerals up to 6 GPa and 500 °C by Raman spectroscopy
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DOI：
10.2138/am-2020-7404
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发表时间：
2021-04-01
影响因子：
3.1
通讯作者：
Redfern, Simon A. T.
中科院分区：
文献类型：
--
作者：
Farsang, Stefan;Widmer, Remo N.;Redfern, Simon A. T.
碳酸盐矿物在深部碳循环中起主导作用。确定碳酸盐岩的高压和高温振动性质对于了解其在地壳和上地幔条件下的非谐性及其热力学性质至关重要。基于我们之前对文石方解石的研究（两种CaCO3多晶型）、白云石[CaMg（CO3）（2）]、菱镁矿（MgCO3）、菱锰矿（MnCO3）和菱铁矿（FeCO3）（Farsang等人，2018），我们已经测量了压力和温度引起的拉曼活性振动模式的频率偏移，高达6 GPa和500摄氏度，对于所有天然存在的文石和方解石，组碳酸盐矿物，包括白铅矿（PbCO 3）、菱锶矿（SrCO 3）、毒重石（BaCO 3）、碳硅钙石（NiCO 3）、钙钛矿（CdCO 3）、菱锌矿（ZnCO 3）和球钴铁矿（CoCO 3）。我们的拉曼和XRD测量结果表明，白铅矿在225至250摄氏度之间分解为Pb2O3和四氧化二铅PbO的混合物，菱锌矿在325至400摄氏度之间分解为六方ZnO，而白铅矿在375至400摄氏度之间分解为NiO。球钴矿在425至450摄氏度之间分解，而奥太维特在375至400摄氏度之间分解。由于它们的热稳定性，碳酸盐可以用作几种金属（例如，Co，Ni，Zn，Cd）在地壳和上地幔环境（例如，俯冲带）。我们已经确定了等压和等温等效的模式Gruneisen参数和非谐参数为每个拉曼模式和比较的趋势，振动特性作为压力，温度和化学组成的函数，伴随着结构特性的变化。最后，利用非谐参数计算了碳酸盐的内能和熵的热贡献，以及等容和等压热容。
Carbonate minerals play a dominant role in the deep carbon cycle. Determining the high-pressure and high-temperature vibrational properties of carbonates is essential to understand their anharmonicity and their thermodynamic properties under crustal and upper mantle conditions. Building on our previous study on aragonite, calcite (both CaCO3 polymorphs), dolomite [CaMg(CO3)(2)], magnesite (MgCO3), rhodochrosite (MnCO3), and siderite (FeCO3) (Farsang et al. 2018), we have measured the pressure- and temperature-induced frequency shifts of Raman-active vibrational modes up to 6 GPa and 500 degrees C for all naturally occurring aragonite- and calcite-group carbonate minerals, including cerussite (PbCO3), strontianite (SrCO3), witherite (BaCO3), gaspeite (NiCO3), otavite (CdCO3), smithsonite (ZnCO3), and spherocobaltite (CoCO3). Our Raman and XRD measurements show that cerussite decomposes to a mixture of Pb2O3 and tetragonal PbO between 225 and 250 degrees C, smithsonite breaks down to hexagonal ZnO between 325 and 400 degrees C, and gaspeite to NiO between 375 and 400 degrees C. Spherocobaltite breaks down between 425 and 450 degrees C and otavite between 375 and 400 degrees C. Due to their thermal stability, carbonates may serve as potential reservoirs for several metals (e.g., Co, Ni, Zn, Cd) in a range of crustal and upper mantle environments (e.g., subduction zones). We have determined the isobaric and isothermal equivalents of the mode Gruneisen parameter and the anharmonic parameter for each Raman mode and compare trends in vibrational properties as a function of pressure, temperature, and chemical composition with concomitant changes in structural properties. Finally, we use the anharmonic parameter to calculate the thermal contribution to the internal energy and entropy, as well as the isochoric and isobaric heat capacity of certain carbonates.