V23D-05
Stable Isotope Evidence for Planetary Differentiation

Tuesday, 15 December 2015: 14:40
310 (Moscone South)
Anat Shahar, Carnegie Institution of Washington, Geophysical Laboratory, Washington, DC, United States, Wendy L Mao, Stanford University, Stanford, CA, United States, Edwin A Schauble, University of California Los Angeles, Los Angeles, CA, United States, Razvan Caracas, CNRS Lyon, Lyon, France, Mary M Reagan, Stanford Earth Sciences, Stanford, CA, United States and Arianna E Gleason, Los Alamos National Laboratory, Los Alamos, NM, United States
Abstract:
Planetary differentiation occurred at high temperature and varying oxygen fugacity, on bodies with varying compositions and internal pressures. The specific conditions at which bodies differentiated and the chemical fingerprints left by differentiation can be investigated by measuring stable isotope ratios in natural samples. Much can be learned by combining those data with experiments that systematically investigate the chemical and physical conditions within differentiating bodies. In this talk we focus on one variable in particular that has not been well defined with respect to stable isotope fractionation: pressure. We will present new iron isotope data on how pressure affects isotope fractionation factors for a number of iron compounds relative to silicate.

The processes governing iron isotope fractionation in igneous rocks have been debated extensively over the past decade. Analyses of natural samples show that iron isotopes are fractionated at both the whole rock and mineral scales. This fractionation has been interpreted to be a result of several processes including a possible signature of high pressure core formation. We have collected new high pressure synchrotron nuclear resonant inelastic x-ray scattering data from Sector 16-ID-D at the Advanced Photon Source on 57Fe enriched Fe, FeO, FeHx and Fe3C. Our data show clear trends with pressure implying that not only does pressure have an effect on the iron isotope beta factors but also a fractionation amongst the alloys. This suggests that depending on the light element in the core, there will be a different resulting signature in the iron isotope record. We will discuss the likelihood of different light elements in the core based on these results, as well as the theoretical predictions for the same phases. Finally, we will present the fractionation expected between metal and silicate at high pressure and high temperature in order to determine if core formation would indeed leave an isotopic signature in the natural rock record.

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