高温高压下铁菱镁矿(Mg1-xFexCO3)自旋相变相图的实验研究

The spin transition, occurred in Ferromagnesite (Mg1-xFexCO3) under high-temperature-pressure, has been a subject of great concern in geoscience. Research suggests that, Ferromagnesite could be stable as denser low-spin state by induction of pressure, which could create a vast reasonable interpretation for the abnormality arised from high-conductivity and low-velocity zone at the lower mantle. However, the P-T-x phase diagram of spin transition has not been reported thus far, which is the basis for the further study of various physical / chemical properties and thermodynamic process of Iron-bearing carbonates at the high-temperature-pressure conditions of Earth's interior.. In this project, the systematical study of P-T-x phase diagram of spin transition will be carried out by the mean of in-situ high-temperature-pressure Raman spectroscopy. Synthetic single crystals by artificially controlling the iron content will be chosen as main study object to avoid adverse impacts of impurities in natural carbonates. Moreover, the understanding of P-T-x phase diagram of spin transition is expected to provide the rigorous experimental support to reveal component/ structural properties as well as thermodynamic process of carbonates in Earth's interior from the perspective of geology geochemistry/geophysics.

铁菱镁矿（Mg1-xFexCO3）在高温高压下的自旋相变已引起了固体地球科学家们的广泛关注。研究表明，在压力驱动下铁菱镁矿可发生从髙自旋向低自旋的转变，其密度由此发生突变，该结果为下地幔出现的低波速、高电导等异常现象提供了合理解释。但迄今为止，尚未有关于铁菱镁矿压力-温度-铁含量的自旋相变P-T-x相图的报道，而它却是未来全面铺开地球内部温压条件下铁镁碳酸盐矿物各种物理/化学性质和过程研究的基础。. 本项目拟以金刚石压腔拉曼光谱原位观测为主要研究手段，以无杂质干扰和铁含量可控的人工合成高纯铁菱镁矿单晶样品而非杂质和铁含量不可控的天然产出单晶样品为研究对象，在高温高压条件下全面系统地研究铁菱镁矿自旋相变的P-T-x相图，从而为人们从地质地球化学和地球物理角度揭示地球内部碳酸盐物质的组成、结构构造、性状和过程提供强有力的实验支撑。

不同化学成分的矿物通常以某种同构形式存在，这与晶体结构中的阳离子取代机制密切相关。在这方面，化学成分、晶体结构和光谱性质之间的校准方程被认为是同构矿物定量研究的核心。本项目以铁菱镁矿的结构、成分和高温高压稳定性研究为核心，对方解石型和钡白云石型碳酸盐矿物进行了系统的研究，构建了精确的结构-物性模型。