Exchange frequency of oxygen isotope reservoirs in the early solar system

High precision Mg isotope measurements have been performed to determine radiogenic Mg-26 of coarse-grained Ca-Al-rich inclusions (CAIs) in two carbonaceous chondrites by secondary ion mass spectrometry using faraday cup multi-collection system. Minerals in each CAI show individual internal isochrones of Al-26-Mg-26 with respect to each own oxygen isotopic composition of minerals. This indicates that O-16-rich and O-16-poor oxygen isotopic environments existed more than 0.45 Myrs in the solar nebula. The switching time scale between O-16-rich and O-16-poor gaseous environments surrounding CAIs was faster than 10 kyrs.