Oxygen isotope and petrological study of silicate inclusions in IIE iron meteorites and their relationship with H chondrites

AbstractThe origin of silicate-bearing irons, especially those in groups IAB, IIICD, and IIE, is poorly understood as silicate should have separated rapidly from molten metal. Here we report the results of high precision oxygen isotope analysis of silicate inclusions in eleven group IIE meteorites and a petrological study of silicate inclusions in ten IIE irons including those in Garhi Yasin and Tarahumara, which have not been described in detail before. Oxygen isotopes have also been analysed in 20 H chondrites to investigate their possible relationship with the IIE irons.Based on petrographic observations and mineral analysis, the silicate-bearing IIE meteorites have been divided into four types according to the nature of their silicate inclusions: (1) primitive chondritic, (2) evolved chondritic, (3) differentiated with >10vol.% orthopyroxene, and (4) differentiated with <10vol.% orthopyroxene. Each meteorite contains a single inclusion type. While inclusions in an individual IIE meteorite tend to show relatively limited Δ17O variation, a wide range of values is seen in the dataset as a whole. Group IIE irons with differentiated silicates, with the exception of Colomera, have a range of mean Δ17O values that is essentially identical to those of the H4-6 chondrites: 0.60–0.77‰ and 0.61–0.76‰, respectively. Colomera inclusions, which are differentiated with