Zinc isotopic variations in ureilites

The Ureilite Parent Body (UPB) was a C-rich planetary embryo disrupted by impact. Ureilites are fragments of the UPB mantle and among the most numerous achondrites. Zinc isotopic data are presented for 26 unbrecciated ureilites and a trachyandesite (ALM-A) from the same parent body. The d(66)Zn values of ureilites range from 0.40 to 2.71% including literature results. Zinc isotopic compositions do not correlate with the compositions of olivine cores, with C and O isotopic compositions, with Zn abundances, nor with shock grades. The wide range of d(66)Zn displayed by the ureilites is chiefly explained by evaporation processes that took place during the catastrophic breakup of the UPB. During breakup, the high temperatures of the UPB mantle allowed Zn to evaporate, regardless of the intensity the shock suffered by the ureilitic debris. For the most shocked of them, post-shock heating permitted greater evaporation, and heavier Zn isotopic compositions. The surface of the UPB was certainly much colder than the mantle before the breakup. Therefore, crustal rocks were probably less prone to Zn evaporation. ALM-A, the sole crustal rock analyzed at present, has a d(66)Zn value (0.67%) significantly higher than those of regular chondrites. This result indicates that its mantle source displayed already non-chondritic Zn isotopic compositions before the breakup of the UPB. (C) 2018 Elsevier Ltd. All rights reserved.