SPP 2404 - Subproject: Electrical conductivity measurements on lower mantle phases to illuminate structures at the core-mantle boundary region

Basic data for this project

Description

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.