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Interfacial Network Geometry

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For mankind the impact of the dynamics of the Earth’s interior on Earth surface processes is often an unpredictable variation between a curse, e.g. Earthquakes, volcanic eruptions and a blessing, e.g. magnetism, habitability, composition of the atmosphere. Rocks are made of mineral grains and the grain boundaries that form a three-dimensional network. This network has an important contribution to mantle dynamic processes, including magma generation/percolation and plate tectonics processes/geochemical cycles. Olivine is the dominant phase of the upper mantle. Until recently, the grain boundary network and its anisotropic frequency distribution nor its dependence on chemical composition where known for rock forming minerals. Therefore, we characterized interfaces in different aggregates of olivine. The different aggregates where synthesized with varying chemical compositions ranging from Mg2SiO4 forsterite to Mg1.8Fe0.2SiO4 and Mg1.0Fe1.0 SiO4 olivine and different additions of incompatible elements that are known to segregate to the interfaces. We characterized the grain boundary character and plane distribution (GBCD and GBPD ) in doped aggregates is diffusion creep and in the disGBS regime using a torsion deformation setup. Because the geometry of the grain boundary network geometry controls percolation of melts, we constrained how the interfacial network geometry changes during melting. We used high end electron microscopy techniques to characterize the geometrically varying interfaces. Grain orientation data from over 4×104 grains, corresponding to more than 6000 mm grain boundary length per sample were used to stereologically extract the geometry of the interfacial network. We found that the interfacial network geometry is affected by segregation and strongly by melting. We provide a first statistical description of these models, that we implemented in first phase-field models. These show a remarkable effect of the network geometry on grain growth and potentially on percolation.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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