Instrumental neutron activation analyses of the most Earth-like meteorites

Gerd Weckwerth

Journal of Radioanalytical and Nuclear Chemistry
January 2014, Volume 299, Issue 1, pp 221-228


C1-carbonaceous chondrites are known to have the highest meteoritic content of volatile elements. Nevertheless, most volatile elements, such as H, He, N and O, are excluded from the accordance with the solar photosphere. In meteoritic material, which condensed closer to the sun, even moderately volatile elements could not completely condense and their C1-normalized concentration ratios with refractory elements are typically depleted. In primitive terrestrial samples these ratios of (lithophile) moderately volatile to refractory elements are even lower. This suggests an accretion of our planet from material, which condensed closer to the sun than all available meteorites surviving in significantly farer distances in the asteroid belt. Evidence to that may come from agreements between most Earth-like meteorites with the depletion pattern of moderately volatile elements in the Earth’s mantle or rather related bulk data. Therefore, two samples from Hammadah al Hamra 073 and Sahara 0182, supposed to be further members of the most Earth-like Coolidge-Loongana grouplet, have been analysed by INAA. Together with two earlier analysed samples from the grouplet the results have been used in fingerprint studies with terrestrial data. In spite of internal spreading due to sampling of inhomogeneous material, the results are in accordance with a volatility-dependent model of depletion. Abundance ratios of Fe relative to Mn, Cr, and Si measured from the grouplet-abundances are depleted relative to calculated data from the total Earth, what can be explained with a 30 %-mantle-stripping from an impact of a Mars-sized body.