Physics
Scientific paper
Jan 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000lpico.997...17b&link_type=abstract
Workshop on Extraterrestrial Materials from Cold and Hot Deserts, p. 17
Physics
Ice, Antarctic Regions, Meteorites, Chondrites, Carbon 14, Frequency Distribution, Weathering, Spectroscopy, Oxidation, Iron Meteorites, Decay Rates
Scientific paper
It has previously been shown that Mossbauer spectroscopy is capable of providing a quantitative measure of weathering in ordinary chondrite (OC) meteorites. Used in conjunction with C-14 terrestrial ages, we have used this method to constrain weathering rates for individual hot desert meteorite populations. Typically, oxidation over time may be effectively modelled using an appropriate power-law, suggesting an initial rapid weathering phase, followed by more gradual oxidation. By quantifying oxidation over time, and modelling the effect of oxidation in destroying samples (from oxidation-frequency distributions) we can derive a decay-rate for meteorites in an accumulation, or a weathering half-life of a meteorite in a population. This, combined with a knowledge of the number of individual meteorites on the ground today, enables an estimate of the flux of meteorites over the lifetime of the site. Hot desert OC's typically show a peak in their oxidation-frequency distribution at 40% (ie. 40% of the iron in a meteorite is ferric): until this point oxidation is accommodated by available porosity; after this point porosity is exceeded and the sample erodes. If this interpretation is correct, the oxidation-frequency distribution describes the response of OC's to a given amount of chemical weathering, and should be similar between different sites. Ordinary chondrites at the Allan Hills, despite their far longer residence times, are found to have a peak in there oxidation-frequency distribution at 10-15%. 25-30% lower than hot desert OC's. In addition (and contrary to earlier studies, although the data show more scatter than is typical of hot desert populations, we have shown that there is a correlation between weathering and terrestrial age for the Allan Hills meteorites, allowing an (approximate) estimate of the rate of weathering over time. The plot of oxidation over time, although indicating much slower weathering rates than for hot desert meteorites, is qualitatively similar in its form: it can be modelled using an appropriate power-law, and shows an initial rapid weathering phase.
Berry Frank J.
Bevan W. R.
Bland Philip A.
Pillinger Colin T.
Smith Bryan T.
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