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dc.contributor.authorKolbus, Lindsay Marieen_US
dc.date.accessioned2017-04-06T15:42:19Z
dc.date.available2017-04-06T15:42:19Z
dc.date.issued2012-04-24en_US
dc.identifier.otheretd-05042012-170907en_US
dc.identifier.urihttp://hdl.handle.net/10919/77063
dc.description.abstractFeldspar minerals are framework aluminosilicates that comprise approximately 60 percent of the Earth's crust. The elastic and thermodynamic properties of this important mineral group are needed for the interpretation of seismic wave velocities, for understanding cation partioning patterns and for the determination of phase boundaries and reactions involving feldspars in the Earth's crust. Until recently, no systematic approach has been applied to describe the structural behavior of feldspars as a function of pressure, temperature and composition. In this thesis, high-pressure and high-temperature X-ray diffraction data were collected for feldspars over a range of compositions which has led to the development a structural model that allows one to predict the structural evolution of feldspars at depth in the Earth's crust. Specifically, the equations of state have been determined for two plagioclase feldspars (An20 and An78) with different states of Al/Si ordering using single-crystal X-ray diffraction. This study has shown that the introduction of Al,Si disorder into plagioclase structures at constant composition softens the structure by 4(1)% for An0, 2.5(9)% for An20 and is essentially zero for An78 compositions. The effect of pressure on the structure of an ordered An20 was also determined up to 9.15 GPa using single-crystal X-ray diffraction and it was found that the dominant compression mechanism involves tilting of the AlO4 and SiO4 tetrahedra. Similarly, high-temperature single-crystal X-ray diffraction data collected from an ordered An26 plagioclase and powder X-ray diffraction collected on a suite of Na-rich plagioclases that were refined using the Rietveld method indicate that the major structural response to increased temperature involves tilting of the tetrahedra. Building on ideas originally proposed by Dr. Helen Megaw, the changes in the conformation of the tetrahedral framework of feldspars can be described in terms of four distinct tilt systems of rigid tetrahedra. This model demonstrates that the fundamental reason for the observed anisotropy and volume change of feldspars lies in the topology of the tetrahedral framework with the greatest contribution attributed to tilt systems 2 and 3.en_US
dc.language.isoen_USen_US
dc.publisherVirginia Techen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectfeldsparen_US
dc.subjectplagioclaseen_US
dc.subjecthigh-temperatureen_US
dc.subjecthigh-pressureen_US
dc.subjectstructureen_US
dc.titleStructural variations of feldspars at high pressure and high temperatureen_US
dc.typeDissertationen_US
dc.contributor.departmentGeosciencesen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineGeosciencesen_US
dc.contributor.committeechairRoss, Nancy L.en_US
dc.contributor.committeememberAngel, Ross J.en_US
dc.contributor.committeememberNestola, Fabrizioen_US
dc.contributor.committeememberLaw, Richard D.en_US
dc.contributor.committeememberSlebodnick, Carlaen_US
dc.type.dcmitypeTexten_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05042012-170907/en_US
dc.date.sdate2012-05-04en_US
dc.date.rdate2016-10-04
dc.date.adate2012-06-05en_US


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