20-EPN2-009: High-precision oxygen isotope composition of Martian meteorites and their components – insights into the accretion history of Mars
Virtual visit by Siw Egdalen, University of Copenhagen (Denmark) to TA2 Facility 22 – Open University Laser Fluorination Oxygen Isotope Facility (UK).
Dates of visit: 24 May – 11 June 2021
Analyses of Martian meteorites and their components predicts the existence of three main geochemical reservoirs on Mars, namely an enriched crust, a complementary depleted lithospheric mantle, and, lastly, a primitive asthenospheric mantle. Investigating the oxygen isotope composition of these reservoirs is critical for a full understanding of the accretion history of Mars. The Δ17 O composition of ~0.3‰, defined by the SNCs is believed to reflect the primary planetary composition of the martian mantle (1). However, analyses of ancient (>4.5 Ga) individual zircons and minerals from the NWA 7533 regolith breccia, record Δ17 O values that are characterized by a much heavier Δ17 O composition and thus different from the SNCs (2,3). A population of young zircons (<1.5 Ga), also from NWA 7533, are derived from a primitive reservoir located in the deep martian interior, as they are characterized by chondritic-like initial Hf isotope composition (4).
The oxygen isotope composition of a single grain from this population, indicate that this reservoir may be characterised by a different Δ17 O than the SNCs. If correct, the SNCs might not be representative of the bulk martian composition, but plausibly reflecting interaction with a heavy Δ17 O surface reservoir. Therefore, a main objective behind this study was to obtain high-precision oxygen isotope composition of 10 SNC meteorites to potentially detect Δ17 O heterogeneity. However, initial results show no isotopic variability, thus suggesting that the SNC source reservoir has not experienced interaction with surface reservoir, or that any heterogeneity has been erased.
Read the full scientific report, with kind permission from Siw Egdalen.
