STUDY ON EXPOSURE AGES OF CHONDRITES BASED ON SPALLOGENIC MN-53

Longlived spallogenic 53Mn was determined in 36 individual chondrites. Combining our data with those available so far in literature (in total 91 53Mn-values of 61 individual stones) a 53Mnproduction rate of 478 ± 84dpm/kg Fe was derived. Based on this figure it was possible to calculate 53Mn-radiation ages for more than 30 stones with Trad ≤ 10 × 106 yr. A comparison of our results with the respective rare gas- and 26Al-exposure ages (so far available) shows that in general a good agreement exists between ages calculated by these three different methods. Only in the case of 'finds', e.g. in Bondoc and some other stones of probably high terrestrial ages. partial losses of 53Mn seem to have occurred. For well preserved objects the 53Mn method is ideal for the estimation of terrestrial residence times. © 1978.