Rachel S. KIRBY^1,2,3, Penelope L. KING¹, and Andrew G. TOMKINS²
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70040]
¹Sesearch School of Earth Sciences, The Australian National University, Acton, Australian Capital Territory, Australia
²School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia
³Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
Published by arrangement with John Wiley & Sons

It has been proposed that IIE iron meteorites formed through impact processes on a parent body that was composed of either the H chondrites or a much-debated fourth ordinary chondrite group, the HH chondrites. To resolve this debate, we have compiled a large dataset for the ordinary chondrites, low-fayalite ungrouped chondrites, and IIE irons, and undertaken a statistical analysis to determine if: (1) the current classification of ordinary chondrite groups is statistically appropriate; and (2) the IIE irons are related to H chondrites or if they represent a distinct group that formed on a “HH” chondrite parent body. We demonstrate that the current classification system based on petrography and olivine and orthopyroxene chemistry is appropriate for the H, L, and LL chondrites. We define a fourth “F chondrite” group consisting of eight, previously ungrouped, very low-Fa Type 3 and 4 chondrites. Statistical analysis of Δ¹⁷O data alone cannot distinguish between the H chondrites and IIE irons, nor between the L and LL chondrites. Furthermore, statistical analyses are unable to distinguish H chondrites from IIE irons in all measures (mineral chemistry, chondrule size, bulk Δ¹⁷O, Ge and Mo isotopic compositions, and bulk siderophile element abundances in metal); there is no evidence for a “HH” chondrite group. These results are consistent with formation of IIE iron meteorites through impact melting and near-surface metal segregation on the H chondrite parent body. This genetic link between H chondrites and IIE irons allows us to understand the geochemical and petrological changes that occurred during planetary formation and evolution.