• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    Experimental studies of iron-magnesium order-disorder in orthopyroxene: Equilibrium, kinetics, and applications

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_td_3108958_sip1_m.pdf
    Size:
    6.347Mb
    Format:
    PDF
    Download
    Author
    Stimpfl, Marilena
    Issue Date
    2003
    Keywords
    Geology.
    Mineralogy.
    Advisor
    Ganguly, Jibamitra
    
    Metadata
    Show full item record
    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 thermodynamic and the kinetics of the Fe-Mg order-disorder process in orthopyroxene were studied by means of thermal annealing experiments at fix fO₂ condition, and single crystal X-raydiffraction to determine the site occupancies. The behavior of Mn on the equilibrium fractionation of Fe-Mg was studied by a series of annealing experiments using a naturally occurring Mn-rich orthopyroxene (donpeacorite). It was shown that, although Mn and Fe preferentially order to the M2 site relative to Mg, Mn has a significantly stronger M2 site preference than Fe. This result implies that when computing the site fractionation for Fe-Mg in Fe-rich Mn-poor orthopyroxene, the small amount of Mn present in the structure should always be totally ordered in the M2 site. The kinetics of the order-disorder reaction was studied as a function of temperature, composition, and fO₂. The results are compatible with the theoretical predicted variation of the rate constant as (fO₂)¹/⁶. The temperature and compositional dependence of the disordering rate constant, K⁺, can be expressed as: ln K⁺(Ord) = - [(36420)/T(K)] min⁻¹ + 29.03 + 4162(XFe) where XFe is the Fe molar fraction of the sample. The thermodynamic and kinetics data of Fe-Mg order-disorder in orthopyroxene permit retirval of cooling rates natural orthopyroxene crystals from their quenched ordering states around the closure temperature (T(C)) of ordering. Thus, I have applied the data to Central Gneiss Complex, British Columbia, and to a diogenite-meteorite which is believed to have originated on Vesta, to constrain their cooling rates. For the Central Gneiss Complex the cooling rate was found to be ∼10-15°C/My at T(C) ∼290°C. This cooling rate is in excellent agreement with that constrained by geochronological data, and implies an exhumation velocity of ∼0.2mm/y. The thermal history inferred for the diogenite-meteorite GRO95555 suggests that the sample underwent very fast cooling at two different rates: a faster cooling at ∼400°C/year as retrieved from modeling of the compositional zoning the orthopyroxene-spinel couple, followed by a slower cooling at ∼5°C/1000y as obtained from the modeling of the observed quenched state in the orthopyroxene. The implication of these rapid but constraining cooling rates on the excavation and burial of the sample in its parent body has been discussed.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Geoscience
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.