Elemental and isotopic compositions of carbonaceous xenoliths in meteorites and of samples returned from comet 81P/Wild 2: an investigation into the diversity of early solar system materials

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2023

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Chondritic meteorites (chondrites) are samples of undifferentiated asteroids, and because chondrites were never melted, they represent fundamental building blocks of the terrestrial planets. Carbonaceous chondrites (CCs) have H and N isotopic compositions similar to Earth’s oceans and atmosphere, respectively, and CCs are therefore a plausible source of Earth’s volatiles. The main components in chondrites are chondrules, which are mm-sized igneous spherules with olivine and/or pyroxene, and fine-grained volatile-bearing matrix. Although chondrules and matrix both formed in the gaseous disk from which the planets formed, the relationship between chondrule formation and matrix is debated, and chondrites on Earth provide us with a limited sampling of the asteroid belt. This dissertation investigates the diversity of chondrules, matrix, and CC materials in the solar system. The first study elucidates the diversity of chondrules with major element, minor element, and O isotopic measurements of olivine and pyroxene returned from comet 81P/Wild 2. The second study investigates the diversity of matrix materials with H and N isotopic measurements of CC xenoliths that were found in meteorites. By comparing our results with chondrites, we conclude that chondrules formed in a limited number of reservoirs and were then widely distributed across the solar system, but matrix materials are more diverse than chondrules, reflecting materials accreted locally, in an asteroid’s feeding zone. A third study examines an unusual halite-bearing CC xenolith in detail. Isotopic measurements constrain the temperature and timing of fluid activity, and point to an origin for this xenolith on a large, cryovolcanically active world.

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Planetology

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