Volcanic Margins Research Consortium
Oxygen and silicon in Earth's core?
Since Francis Birch (1952) proposed the idea that Earth’s core should contain light elements, people have been trying to identify the kind and amount of the light elements in the core. This is one of the biggest and long-standing arguments about the deep Earth. In the seminar, I will talk about my high-pressure experiments on pure iron in a diamond anvil cell (DAC) and thermodynamic modelling of the systems Fe-FeO and Fe-Si. Based on those results, oxygen distribution in the core will be discussed. Also, I will address effects of silicon on the thermal structure of the core. For the pure iron experiments, we developed a new heating technique in the DAC, namely internal resistive heating system. This technique produces much higher temperature than external heating system and much more stable heating than the conventional laser heating technique. We constrained the pressure (P)- temperature (T) location of a phase transition boundary between the hexagonal close-packed (HCP) structure and face-centred cubic (FCC) structure. The thermodynamics of the system Fe-FeO was investigated to the outer core-inner core boundary condition from the latest static high-P-T experiments including our own HCP-FCC boundary. Under the outer core conditions, the addition of oxygen reduces the compressional wave velocity of iron liquid, moving it away from seismologically constrained values. An overall O-rich bulk outer core model is thus excluded. Seismological observations however, suggest the presence of a low-velocity layer with a thickness of 60-70 km at the top of the outer core. The origin of such a low-velocity layer can be explained by an enrichment of oxygen which might be a consequence of chemical interactions between the core and mantle. We also have constructed a thermodynamic model for the HCP-FCC transition and melting in the system Fe-Si based on our new experiments. A major result is that the liquidus temperature of Fe alloy is not changed by the presence of Si at the inner core-outer core boundary, which implies that Si does not significantly affect the thermal structure of Earth’s core.
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The Volcanic Margins Research Consortium (VMRC) provides the petroleum industry with training and research expertise in volcanology, sedimentology and structural geology of volcanic margins. The consortium comprises academic staff at the universities of Durham, Aberdeen, Glasgow, Leicester and CASP, and industry partners involved in the development of hydrocarbon prospects in the North Atlantic Igneous Province and the Faroes-Shetland Basin.
Training takes place during workshops, in the laboratory and on field courses and each industrial partner has the opportunity to fund PhD projects through the member universities.
VMRC Leader: Richard Brown