Oxygen isotopes in HED meteorites and their constraints on parent asteroids
Chuantong Zhang, Bingkui Miao, Huaiyu He
Planetary and Space Science
In Press, Accepted Manuscript, Available online 19 February 2019
“Highlights
• 146 HEDs have similar Δ17O values of −0.240 ± 0.020‰ (2σ) and derive from 4Vesta.
• Oxygen isotopes anomalies of 5 HEDs are caused by external factors.
• 15 oxygen-anomalous HEDs are likely to originate from at least five different asteroids.
• The conclusions are supported by astrophysical and other geochemical studies.”
“The howardite, eucrite and diogenite (HED) clan of meteorites are usually regarded as Vesta meteorites, but there is still serious controversy over whether Vesta is the only parent body for HEDs. Different numbers of HED parent asteroids have been proposed in previous studies of oxygen isotopes. The main controversy is whether the anomalous oxygen isotopic compositions in some HEDs are caused by factors such as terrestrial weathering, addition of exogenous material during brecciation, or a possible primary isotopic heterogeneity of Vesta. To readdress the questions of whether all HED meteorites are from the same parent body, or to constrain the possible number of multiple parent asteroids, the oxygen isotopic data of 166 HED meteorites from the literature are compiled and reviewed here. Among them, 146 HED meteorites have similar Δ17O values of −0.240 ± 0.020‰ (2σ), and the remaining 20 meteorites show oxygen isotopic anomalies (Δ17O values fall outside 3σ from the above mean). Fifteen HED meteorites have anomalous oxygen isotope compositions that cannot be accounted for by terrestrial weathering or the addition of exogenous material, while the oxygen isotope anomalies in the remaining 5 HEDs are caused by the above factors. Based on studies of a number of isotopic and trace element systems, HED meteorites should form from a magma ocean, thus their parent asteroid is highly likely to be homogeneous. This implies that the oxygen isotope variability of HEDs suggest multiple parent bodies for these meteorites, which is supported by arguments from astrophysical and other geochemical studies such as Zn and Cr. In summary, according to the Δ17O values and a number of other observations, we believe that HED meteorites most likely originate from at least 6 different basaltic asteroids.”
