Zircon equilibria in metamorphic rocks

This study defines a number of fundamental principles of zircon equilibria in metamorphic rocks using a combination of traditional metamorphic petrology, trace element geochemistry, experimental petrology, thermobarometry and geochronology. It is demonstrated that solid-state zircon formation in met...

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Main Author: Degeling, Helen Simone
Format: Doctoral or Postdoctoral Thesis
Language:English
Subjects:
Online Access:http://hdl.handle.net/1885/10732
https://doi.org/10.25911/5d7784e53bbb6
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/4/Degeling_H_2002.pdf.jpg
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/7/Degeling%20Thesis%202002.pdf.jpg
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spelling ftanucanberra:oai:openresearch-repository.anu.edu.au:1885/10732 2024-01-14T10:01:25+01:00 Zircon equilibria in metamorphic rocks Degeling, Helen Simone http://hdl.handle.net/1885/10732 https://doi.org/10.25911/5d7784e53bbb6 https://openresearch-repository.anu.edu.au/bitstream/1885/10732/4/Degeling_H_2002.pdf.jpg https://openresearch-repository.anu.edu.au/bitstream/1885/10732/7/Degeling%20Thesis%202002.pdf.jpg en_AU eng b21432934 http://hdl.handle.net/1885/10732 doi:10.25911/5d7784e53bbb6 https://openresearch-repository.anu.edu.au/bitstream/1885/10732/4/Degeling_H_2002.pdf.jpg https://openresearch-repository.anu.edu.au/bitstream/1885/10732/7/Degeling%20Thesis%202002.pdf.jpg Thesis (PhD) ftanucanberra https://doi.org/10.25911/5d7784e53bbb6 2023-12-15T09:38:54Z This study defines a number of fundamental principles of zircon equilibria in metamorphic rocks using a combination of traditional metamorphic petrology, trace element geochemistry, experimental petrology, thermobarometry and geochronology. It is demonstrated that solid-state zircon formation in metamorphic rocks is more likely to occur during retrograde rather than prograde processes. Zircon equilibria in metamorphic rocks is also found to be highly temperature dependent; phases such as garnet and rutile incorporate more Zr with increasing temperature, thereby resorbing coexisting zircon. These findings have profound implications for the interpretation of ages derived from metamorphic zircons. Experimental investigation of the reaction Zr-rutile + quartz -> rutile + zircon reveals a strong temperature dependence on the Zr content of rutile. From experiments, a new geothermometcr is defined based on Zr02 in rutile, in the presence of zircon and quartz: T(OC) = 89297.49 + 0.63(P - 1) / RinK + 33.46 - 273 This thermometer can be used to define temperatures for successive stages of metamorphism by comparing the Zr contents of rutile inclusions in major phases, with the composition of rutile in a quartz matrix. In the 1 apier Complex, East Antarctica, a rutile inclusion in sapphirine records the temperature of peak metamorphism, at 1100°C, 10 kbar. A similar inclusion in cordierite gives a tenlperature of 1060°C, recording the temperature of sapphirine + quartz breakdown. Rutile grains in the matrix in contact with quartz give lower temperatures, as low as - 700°C. Simple calculations using the above formula show that during high grade metamorphism of a rutile-bearing rock, the Zr-content of rutile increase to such an extent that a significant proportion of pre-existing zircon will be resorbed, inhibiting new zircon growth and removing evidence of prior zircon forming events. Any metamorphic zircon present in such a rock must therefore have formed during cooling rather than at peak metamorphic conditions. A ... Doctoral or Postdoctoral Thesis Antarc* Antarctica East Antarctica Australian National University: ANU Digital Collections East Antarctica
institution Open Polar
collection Australian National University: ANU Digital Collections
op_collection_id ftanucanberra
language English
description This study defines a number of fundamental principles of zircon equilibria in metamorphic rocks using a combination of traditional metamorphic petrology, trace element geochemistry, experimental petrology, thermobarometry and geochronology. It is demonstrated that solid-state zircon formation in metamorphic rocks is more likely to occur during retrograde rather than prograde processes. Zircon equilibria in metamorphic rocks is also found to be highly temperature dependent; phases such as garnet and rutile incorporate more Zr with increasing temperature, thereby resorbing coexisting zircon. These findings have profound implications for the interpretation of ages derived from metamorphic zircons. Experimental investigation of the reaction Zr-rutile + quartz -> rutile + zircon reveals a strong temperature dependence on the Zr content of rutile. From experiments, a new geothermometcr is defined based on Zr02 in rutile, in the presence of zircon and quartz: T(OC) = 89297.49 + 0.63(P - 1) / RinK + 33.46 - 273 This thermometer can be used to define temperatures for successive stages of metamorphism by comparing the Zr contents of rutile inclusions in major phases, with the composition of rutile in a quartz matrix. In the 1 apier Complex, East Antarctica, a rutile inclusion in sapphirine records the temperature of peak metamorphism, at 1100°C, 10 kbar. A similar inclusion in cordierite gives a tenlperature of 1060°C, recording the temperature of sapphirine + quartz breakdown. Rutile grains in the matrix in contact with quartz give lower temperatures, as low as - 700°C. Simple calculations using the above formula show that during high grade metamorphism of a rutile-bearing rock, the Zr-content of rutile increase to such an extent that a significant proportion of pre-existing zircon will be resorbed, inhibiting new zircon growth and removing evidence of prior zircon forming events. Any metamorphic zircon present in such a rock must therefore have formed during cooling rather than at peak metamorphic conditions. A ...
format Doctoral or Postdoctoral Thesis
author Degeling, Helen Simone
spellingShingle Degeling, Helen Simone
Zircon equilibria in metamorphic rocks
author_facet Degeling, Helen Simone
author_sort Degeling, Helen Simone
title Zircon equilibria in metamorphic rocks
title_short Zircon equilibria in metamorphic rocks
title_full Zircon equilibria in metamorphic rocks
title_fullStr Zircon equilibria in metamorphic rocks
title_full_unstemmed Zircon equilibria in metamorphic rocks
title_sort zircon equilibria in metamorphic rocks
url http://hdl.handle.net/1885/10732
https://doi.org/10.25911/5d7784e53bbb6
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/4/Degeling_H_2002.pdf.jpg
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/7/Degeling%20Thesis%202002.pdf.jpg
geographic East Antarctica
geographic_facet East Antarctica
genre Antarc*
Antarctica
East Antarctica
genre_facet Antarc*
Antarctica
East Antarctica
op_relation b21432934
http://hdl.handle.net/1885/10732
doi:10.25911/5d7784e53bbb6
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/4/Degeling_H_2002.pdf.jpg
https://openresearch-repository.anu.edu.au/bitstream/1885/10732/7/Degeling%20Thesis%202002.pdf.jpg
op_doi https://doi.org/10.25911/5d7784e53bbb6
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