Master of Science
Planetary Science and Exploration
Bayerisches Geoinstitut, Universität Bayreuth
Accretion and differentiation of planetesimals are critical steps of planetary formation. By studying achondrite meteorites, we can bring further geochemical and chronological constraints on the source and composition of materials and their evolution throughout the protoplanetary disk. Major and trace element analyses for mineral and whole-rock compositions and high-precision isotopic compositions for the short- and long-lived radiochronometers 53Mn-53Cr, 147,146Sm-143,142Nd and 176Lu-176Hf are reported for two eucrites, two diogenites, and three ungrouped achondrites. Of these, NWA 12338 is a newly classified ungrouped achondrite with an anomalously higher Δ17O than mean value of eucrites, and distinguished by the presence of igneous olivine. e142Ndi of carbonaceous achondrites is slightly lower than non-carbonaceous achondrites by ~15 ppm, indicating a s-process nucleosynthetic deficit in the formation reservoir of the former ones. Results on NWA 11001 eucrite suggest that a protracted magmatism on the eucrite parent body persisted for at least 25 Ma after Solar System formation.
Summary for Lay Audience
Achondrite meteorites are extra-terrestrial magmatic rocks which were ejected from the outer silicate-rich layers of planetesimals that formed more than 4.5 billion years ago in the inner Solar System. They can tell us about the first stages of planetary melting and crust-mantle formation, and also about the distinct reservoirs where planetary embryos formed in the protoplanetary disk well before being mixed together in the asteroid belt. Based on isotopic fingerprints such as mass-independent oxygen and chromium isotopic variations, cosmochemists have recently identified two isolated nebular reservoirs which have been named carbonaceous chondrite (CC) and non-carbonaceous chondrite (NCC) reservoirs. We here investigate achondrite meteorites which may be related to these two groups (based on their O-, Cr-isotopic compositions and/or classification) to compare their elemental and isotopic compositions and chronology records. We report their elemental compositions at the mineral and whole-rock scales (e.g., trace elements, via EPMA, LA-ICP-MS and Q-ICP-MS) and the short-lived and long-lived radiogenic and stable isotopic systematics for seven achondrites (53Mn-53Cr, 147,146Sm-143,142Nd and 176Lu-176Hf). Their geochemistry, such as Rare-Earth Element (abbreviated as REE) concentrations normalized to CI chondrites provide information about their igneous history, and the degree of oxidation of their source reservoirs; the radiogenic isotopes tell us about variable timescales of planetary differentiation on different parent bodies; while the stable isotopes (e.g., 178Hf, 145Nd and 54Cr mass-independent isotopic variations) can be used as tracers of planetary reservoirs and irradiation histories. Coupled with literature data on other achondrites, we find that achondrite meteorites preserve isotopic heterogeneities consistent with isolated planetary formation reservoirs with different oxidizing conditions. Additionally, one of our samples, NWA 11001, supports a protracted magmatic history in the eucrite parent body over 25 million years after formation of the Solar System.
Guo, Zhiguo, "Sm-Nd, Lu-Hf, and Mn-Cr isotope geochemistry of achondrite meteorites: implications for the formation reservoirs of differentiated planetesimals" (2019). Electronic Thesis and Dissertation Repository. 6594.