Thermoluminescence and the shock and reheating history of meteorites—II: Annealing studies of the Kernouve meteorite

Abstract

Samples of the unshocked, equilibrated chondrite, Kernouve (H6), have been annealed for 1–100 hours at 500–1200°C, their thermoluminescence sensitivity measured and Na, K, Mn, Ca and Sc determined by instrumental neutron activation analysis. The TL sensitivity decreased with temperature until by 1000°C it had fallen by 40%. The process responsible has an activation energy of ~8 kcal/mole and probably involves diffusion. Samples annealed 1000–1200°C had TL sensitivities 10 −2 times the unannealed values, most of the decrease occurring ~1100°C. This process has an activation energy of ~100 kcal/mole and is probably related to the melting of the TL phosphor, feldspar, with some decomposition and loss of Cs, Na and K. Meteorites whose petrography indicates healing > 1100°C by natural shock heating events (shock facies d-f). have TL sensitivities similar to samples annealed > 1100°C. Our own and literature compositional data indicate that TL is more stable to annealing than Ag, In, Tl, Bi, Zn and Te and less stable than Na, K, Mn, Ca, Se and Co, while the TL decrease resembles very closely the pattern of Cs loss on annealing.