Heterogeneous isotopic anomalies of SM and GD in the Norton County meteorite: Evidence for irradiation from the active early sun

Abstract

Large and heterogeneous isotopic variations of 150Sm/ 149Sm and 158Gd/157Gd due to neutron capture reactions caused by cosmic-ray irradiation were found in chemical and mineral separates from the Norton County meteorite. The light-colored separates, consisting mainly of enstatite (Mg2Si2O6), have a very large neutron fluence of 1.98× 1017ncm-2, which is 10 times higher than that of the whole rock. Furthermore, four chemical separates showed a large variation in neutron fluences, ranging from 1.82× 1016 to 1.87× 1017ncm-2. The variable amounts of neutron fluences from a small single fragment of the Norton County meteorite cannot be simply explained by single-stage cosmic-ray irradiation in space. Rare earth element (REE) analyses revealed that the fractions with high neutron fluences have similar chemical properties to those in the early condensates in the solar system, showing depletions of Eu and Yb in their REE abundance patterns. The data provide evidence for an activity of the early Sun (T Tauri), suggesting the migration of early and intense irradiation materials into the Norton County meteorite's parent body. © 2012. The American Astronomical Society. All rights reserved.