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部的总体目标一致，即更好地了解极端条件下碳酸盐的结构、性质和反应。为了实现这一目标，我们建议使用激光加热的基于dac的研究来确定碳酸盐的稳定性以及碳酸盐与地幔矿物在地球物理相关条件下的反应。我们将用基于dft的原子模型来补充实验研究，以便能够定量地解释光谱并推导热物理参数。碳酸盐在高压和高温下的相稳定性：对系统中末端成员（Ca,Mg,Fe）CO3的稳定性进行了广泛的研究。CaCO3和MgCO3在与深部地幔对应的压力和温度条件下作为纯相具有化学稳定性，但经历了一系列的结构相变。相比之下，纯FeCO3分解成具有意想不到的化学计量和氧化铁的碳酸盐的新相。大多数碳酸盐铁的新相只有在高压和高温下才稳定。以前对系统（Ca,Mg,Fe）CO3中固溶体行为的研究通常局限于较高压力下的环境温度研究或中等压力下的较高温度研究。因此，在地幔条件下，我们对系统（Ca,Fe,Mg）CO3中二元和三元固溶体的稳定性的了解有很大的差距。因此，我们建议继续我们的研究，以确定（Ca,Fe,Mg）CO3的二元或三元固溶体在高压和高温下的原位x射线衍射和原位拉曼和荧光光谱相图。碳酸盐与地幔矿物的反应：通过对金刚石包裹体的分析推断出地幔中碳酸盐熔体的存在。这种碳酸盐岩熔体可能是地幔中化学元素重新分配的原因。然而，以往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-硅酸盐相互作用过程中微量元素分配的数据，本研究旨在弥补这一空白。虽然一些研究表明，x射线荧光光谱（XRF）可以用于微量元素的原位研究，但XRF在高p，T的原位研究中的适用性是有限的。因此，我们建议使用掺杂样品，这将使我们能够在激光加热金刚石砧细胞实验中使用原位时间分辨激光荧光光谱，拉曼光谱和x射线衍射来确定反应过程中微量元素的分布。

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.