Type of Thesis
Stephen J. Mojzsis
Nigel M. Kelly
Dynamical simulations of planet formation have started to successfully combine cosmochemical tracers such as nucleosynthetic anomalies of measured samples with proposed accretion reservoirs to reveal new information about early solar system processes. As sampled terrestrial planets have over-abundances in the highly siderophile elements (HSEs), it is possible that Earth and Mars experienced significant mass augmentations (~1 wt. %) in one or more Late Veneer (LV) colossal impacts. Additional evidence for LVs may be traceable by isotopic signatures in the crust and upper mantle of the planets; this would be especially true for Mars which has much more sluggish geodynamics than Earth, and may therefor better preserve primordial isotopic heterogeneities. To investigate for a record of Mars’ late accretion, I measured the multiple O-isotopic compositions (16O, 17O, 18O; expressed in conventional Δ17O-notation) in fragments of the martian meteorite, NWA7034. Analysis shows that discrete domains in this ancient martian regolith breccia record anomalous Δ17OVSMOW values compared to the Shergottite-Nakhlite-Chassigny-ALH84001 baseline composition of Δ17OVSMOW = 0.3‰. To account for Δ17O values in NWA7034 as high as +1‰, I propose that a minimum admixture of approximately 22 wt.% LL-Ordinary Chondrite (OC). If Mars’ LV was delivered by an object approximately the mass of Ceres (9´1020 kg; ~1000 km diameter) but with an OC composition, this places the martian LV at odds with Earth, which was affected by an Enstatite Chondrite-type mass augmentation in its late accretion history after the Moon-forming event. I attribute this difference in outcomes to Mars’ proximity to the asteroid belt.
Alexander, Amanda, "The nature and origin of ancient oxygen isotopic heterogeneities in Mars’ crust" (2018). Undergraduate Honors Theses. 1773.