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Formation conditions of plagioclase-bearing type I chondrules in CO chondrites : a study of natural samples and experimental analogs


Please use this identifier to cite or link to this item: http://hdl.handle.net/1928/12629

Formation conditions of plagioclase-bearing type I chondrules in CO chondrites : a study of natural samples and experimental analogs

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dc.contributor.author Wick, Molly
dc.date.accessioned 2011-06-01T17:13:34Z
dc.date.available 2011-06-01T17:13:34Z
dc.date.issued 2011-06-01
dc.date.submitted July 2010
dc.identifier.uri http://hdl.handle.net/1928/12629
dc.description.abstract Chondrites are samples from undifferentiated asteroids that contain components that formed in the early solar system. One of the components found in chondrites is chondrules, which are small igneous spherules that formed from the melting of precursor dust ball assemblages during very short, high-temperature events in the solar nebula. Chondrules typically contain olivine and pyroxene, a glassy mesostasis, Fe-Ni metal, and sulfides. Type I chondrules contain FeO-poor and volatile-poor mineral assemblages. Approximately 10% of type I chondrules, including type IA, IAB, and IB textures, also contain igneous plagioclase. While dynamic cooling experiments have put constraints on the formation conditions of chondrules based on olivine and pyroxene textures and morphologies, plagioclase has not been produced in previous experimental chondrule analogs. In this study, we investigated common chondrule textures in CO chondrites and determined mineral and bulk compositions for plagioclase-bearing type I chondrules in CO chondrites. We also performed one-atmosphere dynamic cooling experiments in order to establish formation conditions for type I chondrules. We attempted to optimize conditions for plagioclase nucleation and growth by conducting experiments at slow cooling rates, low quench temperatures, in the presence of a Na-rich atmosphere, and with anorthite seeds present in the starting material. Experimental run products closely resemble textures of type I chondrules in ordinary and carbonaceous chondrites. Olivine is commonly poikilitically enclosed in euhedral low-Ca pyroxene. Ca-pyroxene appears as overgrowths on larger low-Ca pyroxene grains. Compositions of olivine, pyroxene, and mesostasis from experimental charges are also very similar to those observed in natural chondrules. Therefore, peak temperatures (1500 - 1600°C) and slow cooling rates (5 - 25°C/hr) used are plausible conditions for type I chondrule formation. These conditions are also predicted by the shock wave model for chondrule formation. While our experiments were conducted at conditions that we considered optimized for plagioclase crystallization, plagioclase was not observed in any experiment. Defining the conditions necessary for plagioclase nucleation may place important constraints on chondrule thermal histories. en_US
dc.description.sponsorship National Aeronautics and Space Administration en_US
dc.language.iso en_US en_US
dc.subject Chondrule en_US
dc.subject Petrology en_US
dc.subject Chondrite en_US
dc.subject Experiment en_US
dc.subject Kainsaz en_US
dc.subject CO en_US
dc.subject.lcsh Chondrules.
dc.subject.lcsh Chondrites (Meteorites)
dc.subject.lcsh Plagioclase.
dc.title Formation conditions of plagioclase-bearing type I chondrules in CO chondrites : a study of natural samples and experimental analogs en_US
dc.type Thesis en_US
dc.description.degree Earth and Planetary Science en_US
dc.description.level Masters en_US
dc.description.department University of New Mexico. Dept. of Earth and Planetary Sciences en_US
dc.description.advisor Jones, Rhian
dc.description.committee-member Shearer, Charles
dc.description.committee-member Brearley, Adrian
dc.description.committee-member Selverstone, Jane

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