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What does the pallasite meteorite “Fukang” tell us about core-mantle interaction in Earth-like planets?

Dr Jason Harvey, Dr Chris Davies, Dr Andrew Walker

The dynamics of Earth’s liquid iron outer core are crucial in the generation of the magnetic field that shields life from the harmful solar wind. But the core’s inaccessibility, buried beneath almost 3000 km of rock, means that we are limited to studying it indirectly via geophysical and geochemical methods. An alternative approach to the study of planetary cores will be explored in this project. Pallasite meteorites consist of rocky particles embedded in an iron rich body, and a number of competing theories exist as to their formation. Historically, these meteorites have been considered to represent the core-mantle boundary of a small planet obliterated early in the history of the solar system. If this were the case pallasites would provide a direct sample of the outer core of a planet; something that we cannot hope to find on Earth. An alternative hypothesis is that the main group pallasite meteorites represent more than one impactor and possibly more than one target planetesimal and that what is actually preserved is the Fe-metal core of an impactor (or impactors) mixed with the mantle of one or more target planetesimals. The aim of this project is to test two possible origins of pallasites using the meteorite “Fukang”. A combination of geochemical microanalysis and numerical modeling of the thermal evolution of the planet, will be compared to information already gathered for the main group pallasites “Imilac” and “Esquel” to help determine the minimum number of bollides and target planetesimals necessary to account for the observed variability in pallasite composition.

The project will involve the geochemical analysis of the pallasite meteorite “Fukang”. This will use several in-situ techniques available in the electron optics suite within the School of Earth and Environment. In this aspect of the project we will prepare the meteorite sample for semi-quantitative scanning electron microscopy and quantitative analyses of the constituent components of the meteorite using an electron probe micro-analyser. We will also obtain trace element compositions of these components using laser ablation inductively couple plasma mass spectrometry. This will not only enable us to estimate the depth at which the pallasite formed inside its parent body, but also evaluate the extent of any chemical differences that might be associated with observed textural heterogeneities observed within the main group pallasites.

There are a number of physical inconsistencies and simplifications in current models relating to pallasite parent bodies. Building on models developed for the Earth, we will estimate the thermal evolution of a possible pallasite parent body and use this to constrain the depth of formation of the main group pallasites. Importantly, not only will this will allow us to relax the simplifications embodied in the currently published results and establish a realistic depth range for formation, but also help us to determine (i) whether one or more parent bodies are required for the main group pallasites and (ii) whether or not pallasites are samples from the core-mantle boundary of an Earth-like planet.

This is a multi-disciplinary project that combines numerical modelling with the analysis of extra-terrestrial material and presents a unique opportunity for a numerate individual who is curious about planetary evolution.