THE NATURAL THERMOLUMINESCENCE OF METEORITES .4. ORDINARY CHONDRITES AT THE LEWIS CLIFF ICE FIELD

Natural thermoluminescence (TL) measurements have been made on 302 meteorites from the vicinity of the Lewis Cliff in the Beardmore region of Antarctica. The data provide information on terrestrial age and unusual radiation and thermal histories, which, in turn, are helpful in identifying fragments of a single fall and in understanding ice sheet movements and the mechanisms by which meteorite concentration occurs at this site. The present data with data for induced TL, class, find location, hand-specimen descriptions and mineral composition have enabled 70 of the present samples to be assigned to 27 groups of "paired" meteorites, with between 5 and 2 meteorites in each group. The distribution of meteorites on the ice, the shape of the fields of "paired" meteorites, and trends in the natural TL data indicate that there is a western component to the movement of the ice at this location, as well as the previously supposed movement to the north. This western vector probably explains the concentration of meteorites along the western edge of the ice tongue. Meteorites at the northern end of the tongue (the Lower Ice Tongue), and Meteorite Moraine to the east, have relatively high natural TL, and therefore young terrestrial ages, while those on the upper tongue show a broad range of ages including a great many large ages. Details of the meteorite concentration are different on the Upper and Lower Tongue and it might be that these two parts of the ice sheet are unrelated. These new natural TL data identify several recent falls and several meteorites which probably had unusually small perihelia immediately prior to capture by the earth.