Richard C. Greenwood^a, Jean-Alix Barrat^b, Akira Yamaguchi^c, Ian A. Franchi^a, Edward R.D. Scott^d, William F. Bottke^e, Jenny M. Gibson^a

^aPlanetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
^bCNRS UMR 6538 (Domaines Océaniques), U.B.O.-I.U.E.M., Place Nicolar Copernic, 29280 Plouzané Cedex, France
^cNational Institute of Polar Research, Tokyo 190-8518, Japan
^dHawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822, USA
^eSouthwest Research Institute and NASA Lunar Science Institute, 1050 Walnut Street, Suite 400, Boulder, CO 80302, USA

Oxygen isotope measurements of a suite of 22 diogenites demonstrate that they have a restricted range of Δ¹⁷O values: . These results indicate that the diogenites form a single population consistent with a single parent body source, rather than multiple sources as has recently been suggested. Our previously published analysis of eucrites and cumulate eucrites (n=34) give very similar results to the diogenites, with  and confirm that diogenites and eucrites are from the same parent asteroid. The isotopic homogeneity displayed by diogenites, eucrites and cumulate eucrites, provides strong evidence for an early large-scale melting event on the HED parent body, possibly resulting in the formation of a magma ocean. The paradox, whereby diogenites show isotopic evidence in favor of global melting, but also geochemical features indicative of late stage interaction with eucritic crust, may reflect a rapid transition from global to serial magmatism on their parent body. The fact that all the lithologically varied HED units have an isotopically homogeneous composition supports the proposal that they are derived from a single, large, diverse asteroid, most likely 4 Vesta. The recent suggestion that the HEDs are not from Vesta, but instead represent material from the same asteroidal source as the main-group pallasites and IIIAB irons can be excluded by our oxygen isotope data.

Reference
Greenwood RC, Barrat J-A, Yamaguchi A, Franchi IA, Scott ERD, Bottke WF and Gibson JM (2014) The oxygen isotope composition of diogenites: Evidence for early global melting on a single, compositionally diverse, HED parent body. Earth and Planetary Science Letters 390:165–174.
[doi:10.1016/j.epsl.2013.12.011]
Copyright Elsevier

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