22-EPN3-036: Investigating Titanium and Chromium Isotopes in Unusual Achondrite NWA 8564
Visit by Julia Cartwright of University of Alabama (USA) to TA2.14 ETH Zurich Geo- and Cosmochemistry Isotope Facility (Switzerland).
Dates of visit: 10-22 July 2023
Report Summary: We pursued high-precision chromium (Cr) and titanium (Ti) isotopic analysis to better refine the parent body of little-studied unusual achondrite Northwest Africa (NWA) 8564. While originally classified as a cumulate eucrite, NWA 8564 displayed unusual lead (Pb) data, suggestive of contributions from an exotic component, thus calling into question its assumed parent body, asteroid 4-Vesta. In this work, we sampled, prepared, and dissolved materials from NWA 8564, eucrites Juvinas and Tirhert, alongside diogenite NWA 7831 and a terrestrial standard to determine the parentage of NWA 8564.
Samples were selected, sampled and sent to ETHZ to be crushed and taken through dissolution and column chemistry. As Cr and Ti isotope analysis require different schedules, the chemistry and analysis stages were staggered for efficiency (e.g., three Ti columns and the first stages of Cr column cleaning were performed prior to Ti arrival). During the visit, the Cr separation procedure was carried out and preliminary analyses were performed after the visit. Eluted Ti aliquots were assessed for content and subsequently diluted for MC-ICP-MS analysis in week 1. Following data assessment/reduction, further aliquots were prepared through week 2, resulting in ~4 sessions of Ti data. The preliminary results show Ti and Cr isotope values for NWA 8564 within the range of eucrites. This suggests that NWA 8564 originates from Vesta, and must have experienced a significant event on Vesta that affected the Pb isotope data. This may include remelting associated with a large impact, potentially linked to the large, ancient basins at Vesta’s south pole.
