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SUMMARY:Interfacial Network Geometry - Katharina Marquart (Imperial Colleg
 e London)
DTSTART:20191203T120000Z
DTEND:20191203T130000Z
UID:TALK129151@talks.cam.ac.uk
CONTACT:Oliver Shorttle
DESCRIPTION:For mankind the impact of the dynamics of the Earth’s interi
 or on Earth surface processes is often an unpredictable variation between 
 a curse\, e.g. Earthquakes\, volcanic eruptions and a blessing\, e.g. magn
 etism\, habitability\, composition of the atmosphere. Rocks are made of mi
 neral grains and the grain boundaries that form a three-dimensional networ
 k. This network has an important contribution to mantle dynamic processes\
 , including magma generation/percolation and plate tectonics processes/geo
 chemical cycles. \nOlivine is the dominant phase of the upper mantle. Unti
 l recently\, the grain boundary network and its anisotropic frequency dist
 ribution nor its dependence on chemical composition where known for rock f
 orming minerals. Therefore\, we characterized interfaces in different aggr
 egates of olivine. The different aggregates where synthesized with varying
  chemical compositions ranging from Mg2SiO4 forsterite to Mg1.8Fe0.2SiO4 a
 nd Mg1.0Fe1.0 SiO4 olivine and different additions of incompatible element
 s that are known to segregate to the interfaces. We characterized the grai
 n boundary character and plane distribution (GBCD and GBPD) in doped aggre
 gates is diffusion creep and in the disGBS regime using a torsion deformat
 ion setup. \nBecause the geometry of the grain boundary network geometry c
 ontrols percolation of melts\, we constrained how the interfacial network 
 geometry changes during melting. \nWe used high end electron microscopy te
 chniques to characterize the geometrically varying interfaces. Grain orien
 tation data from over 4x104 grains\, corresponding to more than 6000 mm gr
 ain boundary length per sample were used to stereologically extract the ge
 ometry of the interfacial network.\nWe 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 fir
 st phase-field models. These show a remarkable effect of the network geome
 try on grain growth and potentially on percolation. \n
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences
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