Oxygen Isotope Constraints on the Origin of Georgia Tektites
E. F. Albin (Fernbank Science Center)
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., O - SMOW) range from + 6.9 to
+ 10.7 parts per mil. The mean O for Georgia tektites is
+ 9.1 parts per mil. These results are consistent with a O
value reported previously on a single georgiaite . It appears that
the tektites have oxygen isotope ratios similar to igneous and/or
metamorphic rocks. Blum and Chamberlain  argue that since sea water
has a relatively low 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 O values due to mixing
with sea water. An alternative explanation may be that the low
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 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 O
measurements on the resulting glass and then compare the results to the
tektites. References:  Taylor, H.P. and Epstein, S. (1969) J.
Geophys. Res., 74, 6834-6844.  Blum J.D. and Chamberlain C.D.
(1992) Science, 257, 1104-1107.