Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997dps....29.3606a&link_type=abstract
American Astronomical Society, DPS meeting #29, #36.06; Bulletin of the American Astronomical Society, Vol. 29, p.1045
Astronomy and Astrophysics
Astronomy
Scientific paper
Georgia tektites ("georgiaites") are North American tektites that occur in east-central Georgia. In this investigation small chips of tektite material was separated from 24 individual specimens for oxygen isotope analysis. Results have an analytical precision of 0.2% based on duplicate analysis of a NIST silicate standard (NBS-28) and tektites. Oxygen isotope ratios (i.e., delta (18) O - SMOW) range from + 6.9 to + 10.7 parts per mil. The mean delta (18) O for Georgia tektites is + 9.1 parts per mil. These results are consistent with a delta (18) O value reported previously on a single georgiaite [1]. It appears that the tektites have oxygen isotope ratios similar to igneous and/or metamorphic rocks. Blum and Chamberlain [2] argue that since sea water has a relatively low delta (18) O value, its addition to isotopically heavier sedimentary rocks could account for the relatively low oxygen isotope ratios determined for the tektites. Such a model would require vaporization of the target material in order to exchange oxygen between the water and silicates. However, vaporization is not a popular theory of tektite petrogenesis, and since tektites contain very little water, it is difficult to reconcile the low delta (18) O values due to mixing with sea water. An alternative explanation may be that the low delta (18) O values are derived from a crystalline basement or it may be that the sedimentary target rocks at the proposed source crater (i.e., Chesapeake Bay crater) have delta (18) O values similar to that of the tektites. To resolve the issue, it will be necessary to melt samples of the proposed target material and make delta (18) O measurements on the resulting glass and then compare the results to the tektites. References: [1] Taylor, H.P. and Epstein, S. (1969) J. Geophys. Res., 74, 6834-6844. [2] Blum J.D. and Chamberlain C.D. (1992) Science, 257, 1104-1107.
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