TL and ESR of quartz from the astrobleme of Aorounga (Sahara of Chad)

Abstract

The present work was intended to evaluate the time that elapsed since the meteorite fall that produced the giant astrobleme of Aorounga (Sahara of Chad). For this purpose the TL and ESR dating techniques using the additive dose method were applied to quartz grains extracted from an impactite and from a sandstone shocked and baked during the impact. The ESR Al centre was measured and resulted in an age of about 800 ka. The red TL and the blue TL showed unusual TL features: the additive dose response curves were marked by an initial saturated part followed by a second rise at around +0.5 kGy; the peaks showed erratic temperature shifts with dose; fading was observed for high temperature peaks. By comparison with previous work using samples baked by lava flows more than 1 Ma ago and presenting some of those features, it was assumed that the minimum age of the astrobleme was of the same order of magnitude. This is in agreement with other observations. A preliminary explanation for those ageing features is proposed. It is suspected that radiation induced traps contribute to the TL of the studied quartz grains. Most probably the ‘malign-behaviour’ of the quartz grains is also connected with shock effects.