On the chemistry of the Allende inclusions and their origin as high temperature condensates

Abstract

The abundances of 45 elements have been determined in a Ca,Al-rich chondrule from the Allende meteorite. The analytical techniques used were instrumental neutron and gamma activation analyses together with radiochemical neutron activation analysis. The refractory lithophile elements Al, Ca, Ti, Sc, V, Sr, Y, Zr, Nb, REE, Hf, Ta, (W) and U and the refractory siderophile elements Re, Os, Ir, Ru and Pt show a mean enrichment factor of 20 relative to C1-chondrites. Most of the other elements, which have been determined, are depleted relative to C1-chondrites. These measurements confirm the suggestion that non-magmatic processes are responsible for these enrichments. Especially the agreement of the measured abundances with those from the predictions of condensation calculations is excellent. Furthermore, by comparing the concentrations of some elements in a surface piece of the chondrule to a central part, a steep concentration gradient was found for the elements Fe, Mn, Na, K, Cl and Br. This suggests that these elements are of secondary origin, having entered the chondrule through the surface.