Mineralogical and chemical composition and cosmic-ray exposure history of two mesosiderites and two iron meteorites

We performed a comprehensive study of the noble gas isotopic abundances, radionuclide activities, and mineralogical and chemical composition of two mesosiderites and two iron meteorites. For the mesosiderites Dong Ujimqin Qi and Weiyuan, the silicate and the metal phases were studied. The anomalous ataxite Rafruti is not chemically related to any other meteorite class, whereas Ningbo is a type IVA octahedrite. The mineralogy and major and trace element abundances of the silicate phases of Dong Ujimqin Qi and Weiyuan are similar to those of other mesosiderites and distinct from those of the howardites. The cosmic-ray exposure history was studied based on the concentrations of the cosmogenic noble gas nuclei and radionuclide activities. For the iron meteorites, cosmic-ray exposure ages were calculated from the pairs Be-10-Ne-21, Al-26-Ne-21, and Cl-36-Ar-36. Rafruti yields the youngest exposure age of all ataxites (6.8 +/- 1.7 Ma), whereas that of Ningbo with 107 +/- 15 Ma falls within the range observed for the other octahedrites. The parent body break-up times of the mesosiderites Dong Ujimqin Qi and Weiyuan are 252 +/- 50 and 25.9 +/- 5.0 Ma, respectively. We find no evidence for a common break-up event for the mesosiderites and the howardites.