Electrical conductivity measurements on lower mantle phases to illuminate structures at the core-mantle boundary region

解决核-地幔边界(CMB)区域的复杂结构和动力学对于理解地球内部的热和化学演化是至关重要的。这是一项及时而具有挑战性的任务，需要矿物物理、地震学和地球动力学等不同学科的共同努力。地震观测提供了与不同长度尺度的结构有关的一系列低速异常的证据，包括所谓的大低速省(LLVP)和超低速带(ULVZ)。到目前为止，这种特征的起源仍然没有得到很好的限制，尽管它们可能在热和化学上都是不同的结构。然而，由于温度和成分的强烈权衡，仅靠地震速度异常不能解决地幔的三维热化学结构。一种有希望的方法是利用电导率观测的不断提高的分辨率，这可以提供对地幔热化学结构的额外和独立的约束。然而，由于缺乏有关压力(P)-温度(T)条件下主相电导率的实验数据，将电导率可观测数据转化为热/化学模型的尝试在很大程度上受到了阻碍。因此，这项建议的目的是通过提供关于CMB条件下富铁的下地幔相和核幔相互作用产生的矿物组合的电导率的独特数据来解决这一知识差距。这将通过国家或最先进的激光加热钻石砧座(LH-DAC)实验、同步辐射X射线探头和对回收样品的先进微观分析表征相结合来实现。新的实验数据将被用来对压力、温度和下地幔相电导率的成分(例如铁的分数)的依赖关系进行参数化，并生成一个开放访问的电导率数据库，以支持SPP DeepDyn和整个地球科学界的研究。在热/热化学模型中对下地幔电导率进行正演模拟，以及它们与电导率观测的对峙，将为了解最低地幔结构的热化学状态及其与电导率异常的联系提供新的见解。

Resolving the complex structure and dynamics of the core-mantle boundary (CMB) region is crucial to understanding the thermal and chemical evolution of the Earth’s interior. This is a timely and challenging task that requires concerted efforts from different disciplines such as mineral physics, seismology and geodynamics. Seismic observations provide evidence for a range of low velocity anomalies associated to structures of different length scales, including the so-called large low velocity provinces (LLVPs) and the ultra-low velocity zones (ULVZs). The origin of this features remains poorly constrained to date although they are probably both thermally and chemically distinct structures. However, because temperature and composition strongly trade-off, seismic velocity anomalies alone cannot resolve the 3D thermo-chemical structure of the mantle. A promising approach is to take advantage of the increasing resolution of the electrical conductivity observations, which can provide additional and independent constrains on the mantle thermo-chemical structure. Yet, attempts to translate electrical conductivity observables into thermal/chemical models have been largely hampered by the lack of experimental data on the electrical conductivity of main phases at relevant pressure (P)-temperature (T) conditions. The aim of this proposal is thus to address this gap of knowledge by providing unique data on the electrical conductivity of iron-rich lower mantle phases and mineral assemblages generated by core-mantle interactions at CMB conditions. This will be achieved by a combination of state-or-the-art laser-heated diamond anvil cells (LH-DAC) experiments, synchrotron X-ray probes and advanced micro-analytical characterization of recovered samples. The new experimental data will be employed to parameterize the pressure, temperature and composition (e.g. iron fractions) dependence of the electrical conductivity of lower mantle phases and to generate an open access electrical conductivity database to support research within SPP DeepDyn and the whole geosciences community. Forward modelling of lower mantle electrical conductivity in thermal/thermo-chemical models, and their confrontation with electrical conductivity observations, will provide new insights into the thermo-chemical state of lowermost mantle structures and their link to electrical conductivity anomalies.