Multicomponent cation diffusion in aluminosilicate garnets: Theory, experiments and applications.

Persistent Link:
http://hdl.handle.net/10150/185214
Title:
Multicomponent cation diffusion in aluminosilicate garnets: Theory, experiments and applications.
Author:
Chakraborty, Sumit.
Issue Date:
1990
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:
Results from experiments in this work have been combined with existing data to yield tracer diffusivities of divalent cations in natural multicomponent garnets at 10-40 kb, 1100 - 1475°C. For the garnet compositions studied in this work, the activation energy for tracer diffusion of Mn < Fe ≃ Mg, while activation volumes increase in the order Mg < Fe < Mn. These data may be used with theoretical models to calculate the full multicomponent diffusion coefficient matrix as a function of pressure, temperature, composition and oxygen fugacity. An analytical model has been developed to describe the relaxation of compositional zoning in metapelitic garnets during metamorphism. It is found that a significant amount of relaxation occurs during heating and the composition at the core of a garnet crystal is disturbed very early in the process. The extent of relaxation depends on a number of factors which include the grain size, the initial shape of the compositional profile, details of the thermal history and the textural mode of occurrence of the garnet. Complications such as oscillations in a compositional profile may be explained by the mathematical form of the equations describing the process. Graphical representation of the results of this model have been provided that allow quick and easy determination of the extent of relaxation or time scale of metamorphic processes. Calculations using the diffusion data indicate that Fe-Mg exchange geothennometry and Sm-Nd geochronology involving garnets may not yield the peak metamorphic conditions for certain geologically realistic situations. Model calculations on natural assemblages suggest that the diffusion data may be used to yield infonnation on metamorphic processes ranging from time scales to crystal growth rates during metamorphism. Veracity of P-T paths calculated from garnet zoning may also be checked using the diffusion data. Illustrative examples of such calculations have been provided.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geochemistry; Mineralogy
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Ganguly, Jibamitra

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleMulticomponent cation diffusion in aluminosilicate garnets: Theory, experiments and applications.en_US
dc.creatorChakraborty, Sumit.en_US
dc.contributor.authorChakraborty, Sumit.en_US
dc.date.issued1990en_US
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.abstractResults from experiments in this work have been combined with existing data to yield tracer diffusivities of divalent cations in natural multicomponent garnets at 10-40 kb, 1100 - 1475°C. For the garnet compositions studied in this work, the activation energy for tracer diffusion of Mn < Fe ≃ Mg, while activation volumes increase in the order Mg < Fe < Mn. These data may be used with theoretical models to calculate the full multicomponent diffusion coefficient matrix as a function of pressure, temperature, composition and oxygen fugacity. An analytical model has been developed to describe the relaxation of compositional zoning in metapelitic garnets during metamorphism. It is found that a significant amount of relaxation occurs during heating and the composition at the core of a garnet crystal is disturbed very early in the process. The extent of relaxation depends on a number of factors which include the grain size, the initial shape of the compositional profile, details of the thermal history and the textural mode of occurrence of the garnet. Complications such as oscillations in a compositional profile may be explained by the mathematical form of the equations describing the process. Graphical representation of the results of this model have been provided that allow quick and easy determination of the extent of relaxation or time scale of metamorphic processes. Calculations using the diffusion data indicate that Fe-Mg exchange geothennometry and Sm-Nd geochronology involving garnets may not yield the peak metamorphic conditions for certain geologically realistic situations. Model calculations on natural assemblages suggest that the diffusion data may be used to yield infonnation on metamorphic processes ranging from time scales to crystal growth rates during metamorphism. Veracity of P-T paths calculated from garnet zoning may also be checked using the diffusion data. Illustrative examples of such calculations have been provided.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeochemistryen_US
dc.subjectMineralogyen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorGanguly, Jibamitraen_US
dc.contributor.committeememberNorton, Denisen_US
dc.contributor.committeememberDrake, Mikeen_US
dc.contributor.committeememberRuiz, Joaquinen_US
dc.contributor.committeememberVemulapalli, Krishnaen_US
dc.identifier.proquest9108415en_US
dc.identifier.oclc709899388en_US
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