Nickel isotope fractionation in metal oxide deep sea spheres with and without metal cores

Details Nickel isotope fractionation in metal oxide deep sea spheres with and without metal cores Nickel isotope fractionation in metal oxide deep sea spheres with and without metal cores

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..553x&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 553

Physics

1

Deep Water, Iron Meteorites, Metal Oxides, Nickel Isotopes, Ocean Bottom, Spatial Distribution, Spheres, Abundance, Chemical Fractionation, Mass Spectroscopy, Vaporizing

Scientific paper

Type I spheres collected from the deep sea contain wuestite, which may surround either partially or entirely a metal core of generally high Ni content and variable size. The isotopic abundances of Fe and Ni in many spheres show large mass-dependent fractionations of up to 4%/AMU. The fractionations favor the heavier isotopes and are consistent with a Rayleigh-type distillation. Further, the degree of mass fractionation of the Ni seems to correlate inversely with the Ni content of the sphere. We compare the Ni isotope fractionation in type I spheres with and without obvious metal cores. Seventeen type I spheres with masses ranging from 39 to 211 microns were selected for study. Elemental Ni contents and Ni isotope abundances were determined by inductively coupled plasma/mass spectrophotometry. With a few exceptions, the Ni concentrations of the spheres correlate inversely with the degree of mass fractionation of the Ni isotopes. Such a correlation might arise if Ni vaporized from a relatively involatile matirx. Perhaps sphere formation takes place only for extraterrestrial material within a restricted compositional range. Less probably, sphere formation could select for specific physical properties of the incoming material. The results imply that the degree of Fe and Ni retention is almost the same for a mass fractionation of about 1.3%/AMU. This observation allows us to read from the figure the starting Ni content of the precursor metal, namely, 5% referred to the current mass. The spheres with this Ni content belong to group NC and hence contain O. If we assume that all the Fe now occurs as wuestite (FeO), then the initial Ni/(Fe+Ni) ratio must have been about 0.08, a value typical of many Fe meteorites.

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