Phase stabilities of carbonates and reaction between carbonates and mantle minerals at high pressures and temperatures studied in the LH-DAC by Raman and time-resolved laser fluorescence spectroscopy

本项目的科学目标与研究组的总体目标相同，即更好地了解碳酸盐在极端条件下的结构、性质和反应。为了实现这一目标，我们建议使用激光加热的DAC为基础的研究，以确定碳酸盐和碳酸盐和地幔矿物之间的反应在物理相关的条件下的稳定性。我们将补充DFT为基础的原子模型的实验研究，以便能够定量解释光谱和推导热物理参数。碳酸盐在高压和高温下的相稳定性：系统（Ca，Mg，Fe）CO 3的端元的稳定性已被广泛研究。CaCO 3和MgCO 3在对应于深部下地幔的压力和温度条件下是化学稳定的纯相，但经历了一系列的结构相变。相比之下，纯FeCO 3分解成具有意想不到的化学计量的新的铁碳酸盐相和铁氧化物。大多数碳酸铁的新相只有在高温高压下才稳定。以前的研究固溶体在系统（Ca，Mg，Fe）CO 3的行为一般限于环境温度的研究在较高的压力或较高的温度在中等压力下。因此，有一个显着的差距，在我们的知识有关的稳定性系统（Ca，Fe，Mg）CO 3在地幔条件下的二元和三元固溶体。因此，我们建议继续我们的研究，以确定（Ca，Fe，Mg）CO_3的二元或三元固溶体的相图，在高压和高温下使用原位X-射线衍射和原位拉曼和荧光光谱。碳酸盐和地幔矿物之间的反应：在地幔中的碳酸盐熔体的存在，从钻石中的包裹体的分析推断。这种碳酸岩熔体可能是地幔中化学元素重新分配的原因。然而，大多数旨在了解地幔中微量元素分布的研究都依赖于淬火样品。由于没有关于下地幔条件下碳酸盐-硅酸盐相互作用期间微量元素分配的数据，本建议旨在弥补这一差距。 虽然一些研究已经表明，X射线荧光光谱，XRF，可以用于微量元素的分配的原位研究，在高p，T的XRF原位研究的适用性是有限的。在这里，因此，我们建议使用掺杂的样品，这将使我们能够确定在反应过程中使用原位时间分辨激光荧光光谱，拉曼光谱和X-射线衍射在激光加热金刚石砧实验中的微量元素的分布。

The scientific goal of the present project is the same as the overall goal of the Research Unit, namely to better understand the structures, properties and reactions of carbonates at extreme conditions. In order to achieve this goal, we propose to determine the stabilities of carbonates and reactions between carbonates and mantle minerals at geophysically relevant conditions using laser heated DAC-based studies. We will complement the experimental studies with DFT-based atomistic models in order to be able to quantitatively interpret spectra and to derive thermophysical parameters.Phase stability of carbonates at high pressure and temperature: The stabilities of end members in the system (Ca,Mg,Fe)CO3 have been extensively investigated. CaCO3 and MgCO3 are chemically stable as pure phases at pressure and temperature conditions corresponding to the deep lower mantle, but undergo a sequence of structural phase transitions. In contrast, pure FeCO3 breaks down into new phases of iron carbonates with unexpected stoichiometry and iron oxides. Most of the new phases of iron carbonates are stabile only at high pressures and temperatures. Previous studies of the behaviour of solid solutions in the system (Ca,Mg,Fe)CO3 are generally limited to ambient temperature studies at higher pressures or to higher temperature at moderate pressures. There is therefore a significant gap in our knowledge concerning the stabilities of binary and ternary solid solutions in the system (Ca,Fe,Mg)CO3 at mantle conditions. Therefore, we propose to continue our studies to determine the phase diagrams for binary or ternary solid solutions of (Ca,Fe,Mg)CO3 using in situ x-ray diffraction and in situ Raman and fluorescence spectroscopy at high pressure and temperature.Reaction between carbonates and mantle minerals: The existence of carbonatite melt in the mantle was deduced from the analyses of inclusions in diamonds. Such carbonatitic melts can be responsible for the redistribution of chemical elements in the mantle. However, most previous studies aimed at understanding the distribution of trace elements in the mantle have relied on quenched samples. As there are no data on the partitioning of trace elements during carbonate-silicate interactions at lower mantle conditions, the present proposal aims to close this gap. While some studies have shown that x-ray fluorescence spectroscopy, XRF, can be employed for the in situ investigation of partitioning of trace elements, the applicability of XRF for in situ studies at high p,T is limited. Here, we therefore propose to use doped samples, which will allow us to determine the distribution of trace elements during the reaction using in situ time-resolved laser fluorescence spectroscopy, Raman spectroscopy and x-ray diffraction in laser heated diamond anvil cell experiments.