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Science Frontiers ONLINE No. 53: Sep-Oct 1987 |
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Tektite-like objects at lonar crater, india
Arguments about the origin of tektites persist in the scientific literature. A strong consensus has these small, drop like glassy bodies originating when meteors smash into the earth, liquifying themselves and some of the surface rocks. The resulting liquid droplets solidify in flight and when they descend form "strewn fields" hundreds, even thousands, of miles in extent.
The main argument has been over whether the actual impact craters giving rise to the tektites might actually be on the moon instead of the earth. Looking over the literature, one sees that this debate has been characterized by much invective and scientific infighting. Today, most scientists concur that some tektite strewn fields are definitely associated with specific, although distant, meteor craters on the earth's surface. Unfortunately, the large separations of craters and strewn fields add a circumstantial flavor to the evidence.
However, some tektite-like objects are to be found in the immediate vicinities of terrestrial craters, but not in far-flung strewn fields; viz., the Aouelloul Crater in Mauritania, and the Zhamashin Crater in the USSR. Another example has now come to light: the Lonar Lake Crater, a 50,000-year-old impact crater, in the Deccan flood basalts in India.
From the paper's abstract:
"Homogenous, dense glass bodies (both irregular and splash form) with high silica contents ( 67% SiO2) occur in the vicinity of Lonar Crater, India. Their lack of microlites and mineral remnants and their uniform chemical composition virtually preclude a volcanic origin. They are similar to tektites reported in the literature....Our geochemical data are consistent with these high silica glass bodies being impact melt products of two-thirds basalt and onethird local intertrappean sediment (chert). The tektite-like bodies of the impact craters Lonar, Zhamanshin, and Aouelloul are generally similar. Strong terrestrial geochemical signatures reflect the target rock REE patterns and the abundance ratios and demonstrate their terrestrial origin resulting from meteorite impact, as has been suggested by earlier workers."
(Murali, A.V., et al; "Tektite-Like Bodies at Lonar Crater, India: Implications for the Origin of Tektites," Journal of Geophysical Research, 92B:E729, 1987.)
Comment. Obviously, the glassy droplets at the Lonar Crater strongly support a terrestrial origin for tektites. Proponents of a lunar origin can still point out, however, that some strewn fields cannot be associated with any known terrestrial crater. And why doesn't the very recent Lonar Crater have a strew field of tektites somewhere? Ditto for Zhamanshin and Aouelloul. There seems to be much more to learn here.