Noble gases in ten Nullarbor chondrites: Exposure ages, terrestrial ages, and weathering effects

We present concentration and isotopic composition of He, Ne, and Ar in ten chondrites from the Nullarbor region in Western Australia as well as the concentrations of (84)Ke, Xe-129, and Xe-132. From the measured cosmogenic C-14 concentrations (Jull et al. 1995), shielding-corrected production rates of C-14 are deduced using cosinogenic Ne-22/Ne-21 ratios. For shielding conditions characterized by Ne-22/Ne-21 > 1.10, this correction becomes significant and results in shorter terrestrial ages. The exposure ages of the ten Nullarbor chondrites are in the range of values usually observed in ordinary chondrites. Some of the meteorites have lost radiogenic gases as well as cosmogenic He-3. Most of the analyzed specimens show additional trapped Ar, Kr, and Xe of terrestrial origin. The incorporation of these gases into weathering products is common in chondrites from hot deserts.