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SUMMARY:Pore-scale controls on core formation in planetesimals - Marc Hess
 e (University of Texas at Austin)
DTSTART:20160219T090000Z
DTEND:20160219T100000Z
UID:TALK64723@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Co-authors: Soheil Ghanbarzadeh (University of Texas at  Austi
 n)\, Masa Prodanovic (University of Texas at Austin) <span><br><span><br>P
 ore-scale melt distribution is thought to evolve towards textural  equilib
 rium. The topology of these pore-scale melt networks is controlled by the 
  porosity and the dihedral angle at the contact line between two solid gra
 ins and  the melt. I will present three-dimensional computations of textur
 ally  equilibrated melt networks in realistic poly-crystalline materials t
 hat have  been obtained from x-ray diffraction contrast tomography. Our si
 mulations show  strong hysteresis in the topology of melt networks with la
 rge dihedral angles. A  percolation threshold at dihedral angles above 60 
 degrees is generally thought  to prevent rapid core formation in planetesi
 mals by segregation of metallic  melts. However\, primitive achondrites sh
 ow that the incipient melt fractions are  between 25% and 35% and that met
 allic melt is connected despite dihedral angles  of approximately 90 degre
 es. Our simulations show that hysteresis allows such a  high porosity and 
 high dihedral angle melt network to rem ain connected during  drainage of 
 the metallic melt. This provides a mechanism for rapid core  formation in 
 planetesimals by porous flow. Only a very small melt fraction\,  approxima
 tely 1%\, is trapped and left behind in the silicate mantle after melt  se
 gregation. This may provide an explanation for the "excess siderophile  pr
 oblem" in the Earth.</span></span>
LOCATION:Seminar Room 1\, Newton Institute
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