The formation of IIE iron meteorites investigated by the chondrule-bearing Mont Dieu II meteorite

The Mont Dieu II meteorite (MD II) is a 435 kg iron meteorite containing cm-sized silicate inclusions. Based on the concentration of Ni, Ga, Ge and Ir in the metal host, MD II can be classified as a IIE non-magmatic iron. The silicate inclusions possess a chondritic mineralogy and thirteen relict chondrules occur throughout the inclusion. Major element analysis, oxygen isotopic analysis (<1727 O = 0.71 ± 0.02 ‰) and mean Fa and Fs molar contents (Fa15.7 ± 0.4 and Fs14.4 ± 0.5) indicate that MD II originated as an H-chondrite. Because of strong similarities with Netschaëvo IIE, MD II can be classified in the most primitive subgroup of the IIE sequence. 40Ar/3930 Ar ages of 4536 ± 59 Ma and 4494 ± 95 Ma obtained on pyroxene and plagioclase inclusions show that MD II belongs to the old (~4.5 Ga) group of IIE iron meteorites and that it has not been perturbed by any subsequent heating event following its formation. The primitive character of MD II sheds light on the nature of its formation process and on possible relationships to other groups of meteorites, as MD II represents a unique opportunity to study planetary differentiation processes in detail.