Petrologic-geochemical studies of chondritic meteorites: Implications from new types of chondrites.
Item
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Title
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Petrologic-geochemical studies of chondritic meteorites: Implications from new types of chondrites.
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Identifier
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AAI9207135
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identifier
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9207135
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Creator
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Weisberg, Michael Kevin.
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Contributor
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Adviser: Cherukupalli E. Nehru
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Geochemistry | Mineralogy | Geology
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Abstract
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Study of several unclassified meteorites has led to characterization of two new chondrite groups and two unique chondrites, and implications for their origins.;The CR2 chondrites represent a new chondrite group having a unique set of petrologic, chemical and isotopic characteristics. These meteorites are breccias and differences in their bulk chemical compositions (i.e., volatile lithophiles) may be explained by differences in their matrix/chondrule ratios. These chondrites experienced parent body aqueous alteration prior to their final lithification.;ALH85085 has several characteristics which set it apart from any known chondritic group. Its chondrules are smaller (25-75 {dollar}\mu{dollar}m), the majority are cryptocrystalline, and all are volatile (Na, K, S) depleted. FeNi metal is more abundant (40.9 wt.%) and sulfide abundance is low (1.1%). The bulk composition of ALH85085 is lower in Na/Si and S/Si and higher in Ni/Si, Fe/Si and Mg/Si than in other chondritic groups. Ca/Si, Al/Si and Mg/Si ratios are closest of those of CR chondrites.;Bencubbin is an unclassified meteorite breccia consisting mainly of host silicate ({dollar}\sim{dollar}40 vol.%) and host metal ({dollar}\sim{dollar}60%) components, and rare ({dollar}<{dollar}1%) ordinary chondrite clasts and a dark xenolith. Two scenarios are offered for the origin of Bencubbin. One is that Bencubbin components are chondritic and were produced in the solar nebula. Later brecciation, reaggregation and minor melting of the chondritic material resulted in it becoming a monomict chondritic breccia. The alternative scenario is that the Bencubbin components formed as a result of major impact melting on a chondritic parent body. Petrologic, chemical and isotopic data are more consistent with Bencubbin being a brecciated chondrite.;Carlisle Lakes, ALH85151 and Y75302 represent a new grouplet which I call the Carlisle Lakes-type chondrites. They have the highest {dollar}\Delta\sp{17}{dollar}O values (up to 2.91) measured. They are olivine-rich ({dollar}>{dollar}70 vol.%), essentially metal-free, and most olivine is FeO-rich, equilibrated at Fa{dollar}\sb{lcub}38{rcub}{dollar}. Some olivine and pyroxene in chondrules and fragments are zoned and their zoning profiles suggest formation by nebular gas-solid exchange reactions accompanied by condensation of new FeO-rich olivine, utilizing existing olivine surfaces as nucleation sites.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
