Moderately volatile elemental and isotopic variations in variably shocked equilibrated ordinary chondrites from Antarctica

Abstract

Volatile elements, crucial players in planetary evolution, condense at low temperatures from solar nebula. Despite extensive past research, gaps remain in understanding the volatile budget establishment and depletion mechanisms during the early stages of Solar System formation. This study investigates the role of shock events on multiple isotope systems in H6 ordinary chondrites with varying shock and weathering degrees. In this study, we classified fifteen H6 ordinary chondrites from Antarctica for their shock and weathering stages. We report the bulk trace elemental abundances of the samples and focus on Zn, Ga, Cu, and Fe isotope compositions, each with distinct 50% condensation temperatures at 726 K, 968 K, 1037 K, and 1334 K, respectively. Three of those elements (Zn, Ga, and Cu) are moderately volatile and trace elements whereas Fe is a moderately refractory and major element. Zinc, with the lowest condensation temperature in this suite, exhibits the widest range in isotopic fractionation (difference between maximum and minimum delta (δ) values in per mil, expressed as Δ hereafter) in our data set with Δ66Zn = 2.60 ‰. Gallium presents a much narrower range of fractionation with Δ71Ga = 0.62 ‰ while copper is three times lower at Δ65Cu = 0.21 ‰. Iron, with the highest condensation temperature, displays the lowest range with Δ56Fe = 0.18 ‰. Interestingly, we found that these variations in isotopic fractionation do not appear to correlate with the shock stage nor weathering grade of the samples. Our findings suggest that impacts cannot explain the observed isotopic fractionation. Evaporative loss due to thermal metamorphism on the parent body may account for Zn and Ga isotope fractionation but likely represents a minor process. Future research should investigate variously metamorphosed samples using in-situ techniques (e.g., laser ablation MC-IPC-MS or SIMS) to highlight condensation and accretion processes from the early solar nebula.