BORIS Theses

BORIS Theses
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Chronology and Genealogy of Early Solar System Materials from Chromium Isotopes

Anand, Aryavart (2022). Chronology and Genealogy of Early Solar System Materials from Chromium Isotopes. (Thesis). Universität Bern, Bern

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This thesis establishes crucial constrains on the chronology, source, transport and mixing of various solar system materials using high-precision Cr isotopes as chronological and genealogical tools. It includes individual studies based on the determination of radiogenic and nucleosynthetic Cr isotope variations in meteorites and terrestrial impactites with meteoritic contaminations. The first study presents the 53Mn-53Cr isotope systematics in ordinary chondrites constraining the accretion and onset and progressive metamorphism of their parent bodies. Both chromite model ages and isochron ages are obtained that correlate with the petrological grade of the samples and are consistent with an onion-shell structure of the chondrite parent bodies. The oldest chromite model age obtained for type 3 samples along with the established Al-Mg chondrule formation ages constrain the accretion of the parent bodies to ≥2.1 Ma after CAI formation, implying that planetesimal accretion immediately followed chondrule formation. The second study presents chromite/daubréelite model ages from IIAB, IIIAB and IVA magmatic iron meteorites. The model ages are within ∼1.5 Ma after the formation of calcium-aluminium-rich inclusions (CAIs) and define the time of metal core formation in the respective parent bodies, assuming metal-silicate separation was an instantaneous event that induced strong chemical fractionation of Mn from the more siderophile Cr. The calibration of Mn-Cr ages with the established Hf-W ages of samples from the same magmatic iron meteorite groups constrains the initial ε53Cr of the solar system to -0.30 ± 0.05, and thus lower than previously estimated. The third study focuses on the 53Mn-53Cr chronology and ε54Cr-Δ17O genealogy of Erg Chech 002, which is the oldest andesite in the Solar System. Both 53Mn-53Cr isochron and chromite model ages for EC 002 predate the chondrule formation interval or are at the earlier side of this interval. Additionally, neutron-rich 54Cr excesses (nucleosynthetic anomalies) combined with mass-independent isotope variations of 17O provide genealogical constraints on the accretion region of the EC 002 parent body. The 54Cr and 17O isotope compositions of EC 002 confirm its origin in the non-carbonaceous reservoir and overlap with the vestoid material NWA 12217 and anomalous eucrite EET 92023. The fourth study employs Cr isotopes in the identification of the type of impactor involved in the formation of the Dhala impact structure, India. The depleted ε54C isotope composition of the Dhala impact melt breccia D6-57 indicates an inheritance of the composition from an impactor originating in the non-carbonaceous reservoir. Furthermore, the binary mixing calculations using Cr isotopes indicate contamination of ~1.2 wt% from a ureilite or 2-3 wt% from an acapulcoite-like impactor.

Item Type: Thesis
Dissertation Type: Cumulative
Date of Defense: 30 August 2022
Subjects: 500 Science > 550 Earth sciences & geology
Institute / Center: 08 Faculty of Science > Institute of Geological Sciences
Depositing User: Hammer Igor
Date Deposited: 18 Mar 2024 17:13
Last Modified: 18 Mar 2024 23:25

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