Partial Melting on FeO-Rich Asteroids: Insights to the First Stage of Planetary Differentiation

Hdl Handle:
http://hdl.handle.net/10150/228118
Title:
Partial Melting on FeO-Rich Asteroids: Insights to the First Stage of Planetary Differentiation
Author:
Gardner-Vandy, Kathryn Gail
Issue Date:
2012
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The melting of planetesimals was a widespread geologic phenomenon taking place in the early inner solar system. Petrologic and geochemical evidence shows that this melting frequently resulted in full differentiation of planetary bodies into a core, mantle, and crust. The extent of this early planetary melting is evidenced in the breadth of achondrite meteorites. In the achondrite meteorite group, there exist meteorites that experienced low degrees of melting, such that the parent body underwent partial melting and did not fully differentiate. These meteorites, called the primitive achondrites, are a window to the first stage of melting in the early solar system. The primitive achondrites with FeO-poor silicate compositions have been well-studied, but little is known about the formation conditions and history of the FeO-rich primitive achondrites, which includes the brachinites and several ungrouped meteorites.The brachinites are olivine-dominated meteorites with a recrystallized texture that show evidence of partial melting and melt removal on their parent body. The ungrouped primitive achondrites are also olivine-dominated meteorites with a recrystallized texture, but they exhibit a larger range in mineralogy with most being essentially chondritic and containing relict chondrules. In this dissertation, I present a study of the petrology, geochemistry and formation conditions of the FeO-rich primitive achondrites. I analyze the petrology and bulk composition of the meteorites, and I conduct thermodynamic modelling of the mineral assemblages to determine oxidation conditions during their formation. Finally, I attempt to simulate the formation of the brachinite meteorites through 1-atmosphere, gas-mixing partial melting experiments of an FeO-rich chondritic meteorite.These meteorites represent a continuum of partial melting, akin to that seen in the acapulcoite-lodranite clan of primitive achondrites. Mineral compositions and oxygen fugacity formation conditions indicate that the brachinites could have formed from a parent body much like the R chondrites. Gas-mixing, partial melting experiments of a R4 chondrite LaPaz Ice Field 03639 at 1250 °C and an oxygen fugacity of IW-1 create the mineralogy and mineral compositions of the brachinites. The experiments also confirm that the brachinites formed by the partial melting of an FeO-rich chondritic source and not as igneous cumulates.
Type:
text; Electronic Dissertation
Keywords:
Melting Experiments; Meteorites; Partial Melting; Primitive Achondrites; Planetary Sciences; Achondrites; Differentiation
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Planetary Sciences
Degree Grantor:
University of Arizona
Advisor:
Lauretta, Dante S.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titlePartial Melting on FeO-Rich Asteroids: Insights to the First Stage of Planetary Differentiationen_US
dc.creatorGardner-Vandy, Kathryn Gailen_US
dc.contributor.authorGardner-Vandy, Kathryn Gailen_US
dc.date.issued2012-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe melting of planetesimals was a widespread geologic phenomenon taking place in the early inner solar system. Petrologic and geochemical evidence shows that this melting frequently resulted in full differentiation of planetary bodies into a core, mantle, and crust. The extent of this early planetary melting is evidenced in the breadth of achondrite meteorites. In the achondrite meteorite group, there exist meteorites that experienced low degrees of melting, such that the parent body underwent partial melting and did not fully differentiate. These meteorites, called the primitive achondrites, are a window to the first stage of melting in the early solar system. The primitive achondrites with FeO-poor silicate compositions have been well-studied, but little is known about the formation conditions and history of the FeO-rich primitive achondrites, which includes the brachinites and several ungrouped meteorites.The brachinites are olivine-dominated meteorites with a recrystallized texture that show evidence of partial melting and melt removal on their parent body. The ungrouped primitive achondrites are also olivine-dominated meteorites with a recrystallized texture, but they exhibit a larger range in mineralogy with most being essentially chondritic and containing relict chondrules. In this dissertation, I present a study of the petrology, geochemistry and formation conditions of the FeO-rich primitive achondrites. I analyze the petrology and bulk composition of the meteorites, and I conduct thermodynamic modelling of the mineral assemblages to determine oxidation conditions during their formation. Finally, I attempt to simulate the formation of the brachinite meteorites through 1-atmosphere, gas-mixing partial melting experiments of an FeO-rich chondritic meteorite.These meteorites represent a continuum of partial melting, akin to that seen in the acapulcoite-lodranite clan of primitive achondrites. Mineral compositions and oxygen fugacity formation conditions indicate that the brachinites could have formed from a parent body much like the R chondrites. Gas-mixing, partial melting experiments of a R4 chondrite LaPaz Ice Field 03639 at 1250 °C and an oxygen fugacity of IW-1 create the mineralogy and mineral compositions of the brachinites. The experiments also confirm that the brachinites formed by the partial melting of an FeO-rich chondritic source and not as igneous cumulates.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectMelting Experimentsen_US
dc.subjectMeteoritesen_US
dc.subjectPartial Meltingen_US
dc.subjectPrimitive Achondritesen_US
dc.subjectPlanetary Sciencesen_US
dc.subjectAchondritesen_US
dc.subjectDifferentiationen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorLauretta, Dante S.en_US
dc.contributor.committeememberSwindle, Timothy D.en_US
dc.contributor.committeememberGreenberg, Richard J.en_US
dc.contributor.committeememberConnoly, Harold C., Jr.en_US
dc.contributor.committeememberLauretta, Dante S.en_US
dc.contributor.committeememberMcCoy, Timohy J.en_US
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