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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Isotopic fractionation of zinc in tektites
Earth and Planetary Science Letters, Volume 277, No. 3-4, Year 2009
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Description
Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation. For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ66/64Zn = 0-0.7‰ for a diverse spectrum of upper continental crust materials. The elemental abundance of Zn is negatively correlated with δ66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime. © 2008 Elsevier B.V. All rights reserved.
Authors & Co-Authors
Moynier, Frédéric
United States, St. Louis
Washington University in St. Louis
United States, Davis
University of California, Davis
Beck, Pierre
France, Paris
Insu - Institut National Des Sciences de L'univers
Jourdan, Fred
Australia, Perth
Curtin University
Yin, Qingzhu
United States, Davis
University of California, Davis
Reimold, Wolf Uwe
Germany, Berlin
Humboldt-universität zu Berlin
Koeberl, Christian
Austria, Vienna
Universität Wien
Statistics
Citations: 81
Authors: 6
Affiliations: 6
Identifiers
Doi:
10.1016/j.epsl.2008.11.020
ISSN:
0012821X
Research Areas
Environmental
Study Locations
Ivory Coast