Oxygen isotopic ratios of primordial water in carbonaceous chondrites

In this work, I estimate the δ18O and δ17O values of primordial water in CM chondrites to be 55 ± 13 and 35 ± 9‰, respectively, based on whole-rock O and H data. Also, I found that the O and/or H data of Antarctic meteorites are biased, which is attributed to terrestrial weathering. This characteristic O isotopic ratio of water together with corresponding water abundances in CM chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula, where mass-independent O isotopic fractionation and water destruction may have occurred. Another possible mechanism to produce the inferred O isotopic ratio of water would be O isotopic fractionation between water vapor and ice, which likely occurred near the condensation front of H2O (snow line) in the solar nebula. The inferred O isotopic ratio of water suggests that carbonate in CM chondrites formed at low temperatures of <150 °C. The O isotopic ratios of primordial water in chondrites other than CM chondrites are not well constrained.