Implication of Mossbauer spectra on the mixing model of eucrites and diogenites (resulting in howardites)

摘要

In the present communication, we show that Mossbauer spectra of cumulate eucrites are characteristically different from those of non-cumulate eucrites. In cumulate eucrites, iron occupies only one site, i.e. the M2 site in pyroxene crystal lattice, while it is distributed in both M1 and M2 sites in non-cumulate eucrites. We discuss the importance of asymmetric doublet observed in the Mossbauer spectrum of cumulate body, especially in Vissannapeta cumulate eucrite (fallen in Andhra Pradesh, India), where an appreciable asymmetry was observed. The Mossbauer parameters of diogenite almost exactly replicate those of cumulate eucrites, suggesting that they originate from the same magma ocean. Howardites which are mixed eucrites and diogenites, show iron mineralogy which is different from what one would expect from a physical mixture model. The possible reasons for this difference are also discussed.