Identification of the parent bodies of micrometeorites with high-precision oxygen isotope ratios

Oxygen isotopic compositions allow identification of potential parent bodies of extraterrestrial materials. We measured oxygen isotope ratios of 33 large (diameter >500 mu m) silicate melted micrometeorites (cosmic spherules) from Antarctica, using IR-laser fluorination coupled with mass spectrometry. It is the first time that this high-precision method is used on individual micrometeorites. The selected micrometeorites are representative of the influx of extraterrestrial materials to the Earth. Our results show that most micrometeorites are related to carbonaceous chondrites, which is consistent with previous studies. However, 20-50% of them seem to be related to CO/CV carbonaceous chondrites, whereas CM/CR carbonaceous chondrites were thought to be the main source for micrometeorites. Furthermore, similar to 30% of measured samples have oxygen isotope ratios lying above the terrestrial fractionation line, which relates them to ordinary chondrites or other, as yet, unsampled parent bodies.