Classification of the Allan Hills A77307 meteorite

Thermoluminescence (TL) measurements on Allan Hills A77307 (AH), a carbonaceous chondrite found in Antarctica, are compared with those on other chondrite and applied to its classification. Two lithologically different 250-mg samples were ground, freed of magnetic material, and ground again to pass a 100-micron sieve. Aliquots of 4 mg were heated to 500 C, exposed to beta radiation from a Sr-90 source, and heated at a rate of 7.3 C/sec in N2. TL was measured with a photomultiplier tube fitted with thermal and blue filters. Glow curves for AH and for seven other, established CO-type chondrites area presented, all exhibiting two major peaks of TL sensitivity. The peaks for the seven CO-type chondrites are found at 91 + or - 7 C and at 203 + or - 11 C; those for AH at 170 + or - 17 C and at approximately 250 C. This difference is considered significant and not due to random fluctuation or a typical sampling. From this comparison and from consideration of the weathering, preterrestrial-alteration, petrological and compositional evidence on AH, it is concluded that AH is a unique chondrite, possessing both similarities to and differences from the CO class.