~(53)Mn-~(53)Cr evolution of the early solar system

摘要

The model of Cr isotopic evolution presented here, relies on the relative volatility properties of the two elements: Mn-Cr in planetary formation processes. The Mn/Cr ratio of the respective parent bodies correlate in most cases with the K/U ratio. With the exception of Allende inclusions, the ~(53)Mn/~(55)Mn and ~(53)Cr/~(52)Cr isotopic ratios were homogeneous in the solar nebula. The Cr isotopic evolution of the bulk solar system corresponds to the C1 carbonaceous chondrites. In this figure the Earth is isolated within a few million years of the C1 formation, from the solar nebula before complete decay of ~(53)Mn. It has a Cr isotopic composition which is depleted in ~(53)Cr with respect to the solar system as a whole. The parent bodies of the different meteorite classes display various behaviour with no case of Mn enrichment relative to Cr when compared to C1. The ~(53)Mn-~(53)Cr isotopic system is a precise tool for the exploration of the early solar system history, bringing constraints both on time and processes in this phase of the evolution where the face of the planetary system was changing rapidly. The chronology deduced from Mn-Cr systematics, is generally in good agreement with other chronometers.