COOLING HISTORIES OF COPIAPO AND LANDES (IA) IRONS

The cooling rate of one silicate inclusion from Copiapo (IA iron) was determined by means of the multiple fission-track-detector method [P. Pellas and D. Storzer, 1977, in Comets, Asteroids, Meteorites (A. H. Delsemme, Ed.), pp. 335-362, University of Toledo]. The preliminary value comes to 1.1-0.5+0.6°C/my for the temperature range 30-350°C. Within the limits of errors this cooling rate agrees with the less precise value of 0.9-0.5+0.8°C/my obtained for one inclusion from Landes (IA). An extrapolation of the fission-track cooling rate through the temperature interval 500-600°C gives a value of ∼4°C/my in good agreement with metallographic data for IA irons (2-4°C/my). © 1979.