Phase Transformations, Microstructures, and their Seismic Signals from the Earth's mantle

我们对固体地球的认识是建立在不同领域的协同研究基础上的：例如，矿物的相变引起地球内部的物理边界。对这些地区产生的地震信号的分析为我们了解地球的结构、组成和动力学提供了关键信息。由于地球内部的极端压力和温度条件，矿物会发生剧烈的变化，必须在实验室中在现实条件下研究它们的性质。与此同时，地震学是直接观测地球深部结构的少数手段之一，因为地震波形受其传播路径上物质沿着的现今状态的制约，例如，在660公里深处向下地幔的过渡就通过地震学来描述。矿物物理研究表明，这主要是由于矿物林伍德石分解成铁方镁石和硼镁石。我们能否将地球模型超越地震不连续性和矿物反应深度之间的简单比较？我们能否利用边界层的地震信号来描述地球深处的过程？这会改变我们对地球的看法吗？这些都是TIMEleSS项目旨在回答的问题。相变引起材料的结构、密度、弹性性质以及微观结构（即矿物相的排列、晶粒尺寸、晶粒取向和应变）的变化。地球中具有不连续物理性质的边界在地震信号中引起特征。但是，地震学中测量到的部分信号及其与地球深部过程的联系尚未完全了解。这对于深度在600 - 1700 km之间的区域尤其如此，在660 km处具有复杂的反射结构，在中地幔深度处具有小尺度结构，在~1000 km处具有难以捉摸的补充不连续性。在这个项目结束时，我们打算约束和模拟相变和微观结构对这些观测的影响，并使用这些新知识来解释这个深度范围内的物理过程。该项目需要高压/高温实验研究和最先进的原位方法，以了解相关矿物成分相变引起的微观结构。与此同时，我们将进行地震学研究，分析新的波组合，当一起使用时，为破译地幔结构的物理参数提供了更大的可能性。将这两个领域结合起来，可以更好地理解相变、微观结构及其相关地震信号之间的联系。TIMEleSS的目标是开发新的方法，并解决无法通过简单分析热力学相变序列来解释的问题，因为它们涉及地球深处的微观结构和动态过程。

Our knowledge of the solid Earth is built upon concerted research in different fields: For example, phase transformations in minerals induce physical boundaries in the Earth's interior. The analysis of seismic signals arising from these regions brings key information for our knowledge of the structure, composition, and dynamics of the planet. Due to the extreme conditions of pressure and temperature in Earth's interior, minerals undergo drastic transformations and their properties must be investigated in laboratories under realistic conditions. In parallel, seismology is one of the few means of direct observation of deep Earth structures as seismic waveforms are constrained by the present-day state of matter along their propagation path. The transition into the lower mantle at 660 km depth, for instance, has been characterized through seismology. Mineral physics demonstrated that it is mostly due to the decomposition of the mineral, ringwoodite, into ferropericlase and bridgmanite. Can we move our Earth model beyond simple comparison between seismic discontinuities and mineral reaction depths? Can we use seismic signals from boundary layers to characterize processes deep inside the Earth? Will this change our current view of the Earth? These are the questions the TIMEleSS project aims to answer. Phase transformations induce changes in the material's structure, density, elastic properties, but also microstructure, i.e. the arrangement of mineral phases, grain sizes, grain orientations, and strains. Boundaries with discontinuous physical properties in the Earth induce signatures in the seismic signals. But part of the signals measured in seismology and their connection to deep Earth processes are not fully understood. This is especially true for the regions lying between 600 and 1700 km depth, with a complex structure of reflections at 660 km, small scale-structures at mid-mantle depth, and an elusive supplementary discontinuity at ~1000 km. By the end of this project, we intend to constrain and model the effect of phase transformations and microstructures on such observations and use this new knowledge to interpret physical processes in this depth range. This project requires high pressure/temperature experimental studies and state-of-the art in-situ methods for understanding microstructures induced by phase transformations in relevant mineral compositions. In parallel, we will conduct seismological studies to analyze new combinations of waves, that, when used together, offer stronger possibilities to decipher physical parameters of structures in the mantle. Combining these two fields allows to better understand connections between phase transformation, microstructures and their associated seismic signals. TIMEleSS' goal is to develop new approaches and to address questions which cannot be explained by a simple analysis of the sequence of thermodynamic phase transitions as they involve microstructural and dynamic processes deep inside the Earth.