Mn-53-Cr-53 evolution of the early solar system

The model of Cr isotopic evolution presented here, relies on the relative v olatility properties of the two elements: Mn-Cr in planetary formation proc esses. The Mn/Cr ratio of the respective parent bodies correlate in most ca ses with the K/U ratio. With the exception of Allende inclusions, the Mn-53 /Mn-55 and Cr-53/Cr-52 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: d ecay of Mn-53. It has a Cr isotopic composition which is depleted in Cr-53 With respect to the solar system as a whole. The parent bodies of the diffe rent meteorite classes display various behaviour with no case of Mn enrichm ent relative to Cr when compared to C1. The Mn-53-Cr-53 isotopic system is a precise tool for the exploration of the early solar sytem history, bringi ng constraints both on time and processes in this phase of the evolution wh ere the face of the planetary system was changing rapidly. The chronology d educed from Mn-Cr systematics, is generally in good agreement with other ch ronometers. Copyright (C) 1999 Elsevier Science Ltd.