Thermoluminescence of meteorites: Relationships with their K-Ar age and their shock and reheating history

The observations of G. F. Komovsky Meteoritika21 (1961), 64–69] and A. Liener and J. Geiss (in Thermoluminescence of Geological Materials, Academic Press, New York, 1968), that the thermoluminescence (TL) sensitivity of meteorites correlates with their KAr age, have been confirmed using a suite of 22 ordinary chondrites. In order to interpret this observation, meteorite samples have been exposed to doses of α, β and γ radiation comparable with those experienced over the lifetime of the meteorites and given a dose of protons comparable to the total dose received from cosmic rays. There was no increase in TL sensitivity after these treatments, suggesting that, contrary to the ideas of earlier workers, the TL mechanism does not involve radiation damage. The TL sensitivity of meteorites is therefore time independent. On the other hand, samples of meteorite annealed in a furnace at temperatures between 450 and 1250°C for 1 hr suffered up to an order-of-magnitude decrease in TL sensitivity. Similarly, samples of meteorite artificially shocked to pressures of the order of 400 kbar suffered a comparable decrease in TL sensitivity. It is concluded that the correlation between TL sensitivity and K-Ar age is entirely a result of the low K-Ar age meteorites being shocked or reheated. Data on the thermal and mechanical histories of these meteorites, based on ⁴⁰Ar?³⁹Ar, metallographic, and X-ray diffraction studies, seem to be consistent with this finding.