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The Effects of Shear Deformation on Planetesimal Core Segregation: Results From in-Situ X-Ray Microtomography

Kasey A. Todd1, Heather C. Watson2, Tony Yu3, and Yanbin Wang3
1Northern Illinois University
2Rensselaer Polytechnic Institute
3University of Chicago, GSECARS

The Earth formed by the accretion and collision of planetesimals. Isotopic evidence from meteorites suggest that the cores of many planetesimals formed within ~3 My. A global magma ocean inadequately explains core formation in small planetesimals due to insufficient temperatures. In order for these planetesimals to efficiently form cores within such a short time without a magma ocean, a critical melt volume of the metal and sufficient melt connectivity and grain size must exist to attain the required permeability. Shear deformation caused by large impacts may increase the connectedness and permeability of the melt, and thus could have been a contributing factor in the formation of these cores.

The purpose of this work is to test the hypothesis that shear deformation enhances the connectivity and permeability of Fe-S melt within a solid silicate matrix such that rapid core formation is plausible. A rotational press was used to heat and deform a sample of solid olivine + FeS liquid through six steps of rotation, while X-ray microtomography obtained in-situ 3-dimensional images of the sample at each step. The resulting digital volumes were processed and permeability simulations were performed. The permeabilities of the sample at each step of deformation are within uncertainty of one another and do not change with increasing deformation. Additionally, the calculated migration velocity of the sample is not high enough for segregation to take place within ~3 My. Nonetheless, the image processing techniques developed in this study will be of great benefit to future studies utilizing similar methods.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013