Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p33a0998s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P33A-0998
Physics
6040 Origin And Evolution, 6205 Asteroids And Meteoroids, 6240 Meteorites And Tektites
Scientific paper
We have been measuring microcrack porosity in meteorite samples using both computerized point counting of backscatter SEM images and helium-density measurements of hand samples. We are using porosity to learn about the formation and evolution of meteorites and their parent bodies. Observations in previous studies to evaluate weathering models found that porosity in ordinary chondrites tended to be constrained to a relatively narrow field. There was agreement between the two methods of measurement, except for highly weathered finds where the point counting method showed higher values for porosity. In extending the study to a broader range of samples, the same narrow range of porosity values was observed: 2% to 20%. There does not seem to be any consistent pattern between the amount of porosity and the type of meteorite. There are hints that different types of meteorites cluster, but there are not enough samples to make statistically significant conclusions. These observations lead us to propose that microcrack porosity observed in the meteorites may have its origin in a process common to all meteoritic material. One such process is the impact environment that has shaped the bodies on which they formed and from which they were ejected. The subsequent shock wave through the material is very likely the source of this porosity. One way to test this hypothesis might be to examine a suite of material that represents the steps from formation to parent body processing through ejection and transportation to Earth. Initial evaluation of a suite of terrestrial and meteoritic basalts hints that there may be progressively more porosity with more processing. If the microcrack porosity we observe does come from an ejection shock wave, the porosity we are measuring may not tell us much about the early history of meteorites.
Consolmagno Guy J.
Strait Melissa M.
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