The evolution of Na-Ca carbonates at HP and high to low T conditions.

The ubiquitous occurrence of Ca-Mg carbonates on Earth comes together with an intriguing paucity of (earth-)alkaline carbonatitic deposits probably due to the instability of minerals in the CaCO3-(Na,K)2CO3 system at ambient conditions and in presence of meteoric water. However, these minerals are of a great geological importance as possible lowering agents for mantle melting temperature. Moreover, Na-carbonate phases have been recently attributed to the so called “bright spots” on the surface of Ceres, a dwarf planet located on the asteroids belt. The present proposal is aimed to study by single crystal X-ray diffraction the crystal structure evolution of the anhydrous nyerereite [Na2Ca(CO3)2] and the highly water content form, gaylussite [Na2Ca(CO3)2·5H2O], at high pressure and high to low temperature conditions. Obtained results will allow to infer about the inner dynamics and composition of both the Earth and planetary bodies.

钙镁碳酸盐（Ca-Mg carbonates）在地球上分布广泛，但与之伴生的（陆地）碱性碳酸盐岩矿床却极为稀缺，这一现象大概率源于常温常压且存在大气降水的条件下，CaCO₃-(Na,K)₂CO₃体系内矿物的不稳定性。不过，这类矿物作为可降低地幔熔融温度的潜在降温剂，具有重要的地质学意义。此外，科研人员近期将位于小行星带的矮行星谷神星（Ceres）表面的所谓“亮斑”，归因于钠碳酸盐相的存在。本研究计划采用单晶X射线衍射（single crystal X-ray diffraction）技术，探究无水尼雷雷石（nyerereite，化学式Na₂Ca(CO₃)₂）与高含水相盖卢西特石（gaylussite，化学式Na₂Ca(CO₃)₂·5H₂O）在高压及高温至低温区间内的晶体结构演化规律。本研究获取的实验结果，将为推断地球与各类行星天体的内部动力学过程及物质组成提供可靠依据。