Blog
About

1,464
views
2
recommends
+1 Recommend
1 collections
    58
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Formation of nickel–iron meteorites by chemical fluid transport

      This is not the latest version for this article. If you want to read the latest version, click here.

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          ABSTRACT

          The deposition of solid material from the gas phase via chemical vapor transport (CVT) is a well-known process of industrial and geochemical relevance. There is strong evidence that this type of thermodynamically driven chemical transport reaction plays a significant role in certain natural processes. This article presents detailed evidence that CVT is a highly plausible mechanism for the formation of iron meteorites. In this study, naturally occurring CVT is referred to as “chemical fluid transport” (CFT) and the end products deposited from the gas phase as “fluidites.”

          Treating iron meteorites as cosmic fluidites enables simple solutions to be found to the problem of how they formed and to numerous related and in some cases unresolved questions.

          This study is based on a thermodynamic trend analysis of solid–gas equilibrium reactions involving chlorine- and fluorine-containing compounds of 42 chemical elements that include a systematic examination of reaction dominance switching behavior. In order to assess the transport behavior of the individual elements, the reaction-conditioned pressures p MeX were calculated from the equilibrium constants. For a selected group of minerals, the relative propensity of these minerals to deposit from the gas phase was then derived from the equilibrium constants. The study shows that octahedrites, hexahedrites and ataxites formed as a result of the transport of metal chlorides and fluorides (CFT) during accretion within the solar nebula. Siderophile elements are characterized by the similarities in their chemical transport properties. These chemical properties of the elements, expressed in the form of the reaction-conditioned pressure, play a key role in determining the chemical composition of iron meteorites. The mobilization process that leads to the formation of the gaseous metal halides MeX includes the reduction of oxides. The deposition of nickel–iron bodies occurs via back reaction after the transport of the gaseous halides. The back reaction leads to the thermodynamically favored deposition of schreibersite before troilite and of troilite before kamacite/taenite. The deposition temperature of octahedrites and hexahedrites lies below the temperature at which Widmanstätten patterns would be destroyed, while that of ataxites lies slightly above. Similarly, the occurrence of thermally instable cohenite in meteorites provides further support for the fluidite character of irons.

          The variation in the trace element concentrations in iron meteorites is explained by enrichment and depletion mechanisms in the gas phase. The striking correlation between gallium and germanium abundances in iron meteorites is the result of similarities regarding the mobilization phase and the reaction dominance switching behavior of both elements, and crystal isomorphism.

          These findings are supported by numerous arguments that provide evidence for the CFT model. The occurrence of the mineral lawrencite FeCl 2 in meteorites is interpreted as an indication of the effectiveness of the chemical transport of FeCl 2. The presence of meteorite alteration and the observed deviations from the solar elemental abundances in silicate meteorites are also explained in terms of the effectiveness of CFT-based mobilization.

          Related collections

          Most cited references 127

          • Record: found
          • Abstract: not found
          • Article: not found

          Abundances of the elements: Meteoritic and solar

            Bookmark
            • Record: found
            • Abstract: not found
            • Article: not found

            Condensation in the primitive solar nebula

              Bookmark
              • Record: found
              • Abstract: not found
              • Article: not found

              Early chemical history of the solar system

                Bookmark

                Author and article information

                Contributors
                (View ORCID Profile)
                Journal
                SOR-EARTH
                ScienceOpen Research
                ScienceOpen
                2199-1006
                18 October 2017
                October 18 2017
                : 0 (ID: a1508611-358d-4984-ab37-195c415c900c )
                : 0
                : 1-22
                Affiliations
                Kernbergstraße 52a, 07749 Jena, Germany
                Author notes
                [* ]Corresponding author’s e-mail address: weschroen@ 123456gmx.de
                Article
                3852:XE
                10.14293/S2199-1006.1.SOR-EARTH.A2TIA5.v2
                © 2016 Schrön

                This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

                Page count
                Figures: 11, Tables: 4, References: 74, Pages: 22
                Categories
                Original article

                Comments

                Comment on this article