Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..467f&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 467-468
Computer Science
2
Chondrites, Meteoritic Composition, Oxygen Isotopes, Weathering, Climate Change, Geochronology, Mossbauer Effect, Spectroscopic Analysis
Scientific paper
The effects of weathering on the O isotopic composition were studied in a suite of meteorites from Roosevelt County with known terrestrial ages. To determine the extent of terrestrial weathering the samples were first analyzed by Fe-57 Mossbauer spectroscopy. The contribution to the Mossbauer spectra recorded from the ferromagnesian silicates, olivine and pyroxene, for the suite of Roosevelt County meteorites indicate a clear trend showing a decreasing contribution from these phases with increasing terrestrial age. The parallel increase in Fe(3+) and the nature of the new phases show that it is dissolution and oxidation of the meteorites that is destroying iron metal and Fe(2+) phases. The rate of dissolution and oxidation of the ferromagnesian silicates is approximately 6% per 5000 yr. With the Mossbauer method for clearly defining the extent of weathering in each meteorite in a well-constrained environment we have extended the effort to evaluate the possibility of observing concurrent changes in the measured oxygen isotopic composition during erosion. Preliminary results from eight meteorites are presented. Replicate analyses are generally in good agreement. Results appear to indicate evidence for a correlation between O isotopic compositions and terrestrial age, and by inference, degree of weathering. The trend is essentially the reverse of what is expected from a simple system as it is the youngest, least-weathered meteorites, which display the largest shifts in (delta)O-18 from a typical chondrite fall. The exact nature of the relationship between the degree of weathering and the oxygen isotopic composition of the meteorites is unclear, highlighting, the complex effects of weathering and the caution required when interpreting results from finds.
Berry Frank J.
Bland Phil
Franchi Ian A.
Pillinger Colin T.
Speck Angela
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