22-EPN3-038: Asteroidal source(s) of L chondrites and its collisional evolution
January 23, 2024

22-EPN3-038: Asteroidal source(s) of L chondrites and its collisional evolution – U,Pb geochemistry of phosphates in meteorite Antonin.

Visit by Monika Kusiak (Institute of Geophysics Polish Academy of Sciences (IG PAS), Poland) and Agata Krzesinska (University of Oslo) to TA2 Facility 26 – KBSI Sensitive High Resolution Ion MicroProbe / SHRIMP-IIe/MC (South Korea).
Dates of visit: 12-23 May 23

Report Summary: The main goal of the visit was to conduct in-situ U-Pb geochronological study of phosphate minerals in the Antonin L chondrite. Fall of the Antonin, on 15th July 2021, was recorded by European Fireball Network, and this recording led to reconstruction of the pre-atmospheric orbit of meteoroid. The orbital parameters of the Antonin differ from reconstructed orbits of other L chondrites, but suggest it was sourced from the inner asteroid belt. To track the orbit to the parent body, it is important to understand dynamic collisions experienced, which are recorded in minerals of the meteorite. U-Pb dating allows to decipher details on events that led to resetting of phosphates.

During the visit to KBSI facility, we collected SHRIMP (Sensitive High-Resolution Ion MicroProbe) analyses within multiple apatite and merrillite grains. Initial U-Pb results show minor discordance of ages of phosphates, indicating a mild collision after the crystallization of the minerals. The timing of reset event cannot be inferred with high precision, but it likely occurred between 500–100 Ma.

Additionally, formation of phosphates can be well constrained from collected data at ca. 4450 Ma. This age implies that phosphates formed/recrystallized in response to a collision as impacts were the only source of heat after cessation of accretional activity. Altogether, the results suggest two collisions in the evolution of parent body and will be combined with further data to pinpoint key events in dynamical evolution of parent body of L chondrites.