20-EPN2-030: The O-isotope signatures of aqueously altered micrometeorites – probing the CO-CM gap and the diversity of C-type asteroids

Virtual visit by Jacopo Nava, University of Padova (Italy) to TA2 Facility 21 – OU NanoSIMS 50L (UK).
Dates of visit: 6-26 July 2022

Report Summary: The flux of extraterrestrial material falling to Earth is dominated by micrometeorites. They originate from asteroids and comets and their analysis provides a complementary perspective to the insights obtained from the study of larger meteorites and from space mission sample returns. Oxygen isotope compositions can be used to match micrometeorites to parent body sources based on distinctive δ¹⁷O and δ¹⁸O ratios.

We studied a population of seven giant Antarctic micrometeorites using high-precision, spatially resolved oxygen isotope analyses to measure the composition of fine-grained matrix in hydrated and dehydrated micrometeorites. 

A characteristic feature of all micrometeorites was large intrasample isotopic variation (>15‰ in δ¹⁸O). In addition, most particles could be matched to known meteorite groups, including identification of CM, CV, CR and, potentially CY parentage. This is consistent with petrographic studies which conclude that the micrometeorite flux is dominated by material from hydrated carbonaceous chondrite asteroids. One particle (TAM5-30) has petrographic characteristics intermediate between the CO and CM chondrite groups. Oxygen isotope analyses of its fine-grained matrix plot either in the CO or CM chondrite fields. This particle is interpreted as a CO-like C2 ungrouped chondrite and may represent material from an otherwise unsampled parent body.

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