Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry
A zircon grain in an orthopyroxene-garnet-phlogopite-zircon-rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal-plastic deformation. The zircon grain records significant variations in titanium (Ti...
| Main Authors: | , , , , , |
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| Format: | Journal Article |
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Elsevier Science BV
2011
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| Online Access: | http://hdl.handle.net/20.500.11937/40878 |
| _version_ | 1848755988897726464 |
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| author | Timms, Nicholas Eric Kinny, Peter Reddy, Steven Evans, Katy Clark, Chris Healy, David |
| author_facet | Timms, Nicholas Eric Kinny, Peter Reddy, Steven Evans, Katy Clark, Chris Healy, David |
| author_sort | Timms, Nicholas Eric |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | A zircon grain in an orthopyroxene-garnet-phlogopite-zircon-rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal-plastic deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U-Pb ages from more deformed zones (mean age of 1799 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 65 Ma, n = 7), and indicate that open system behaviour of Ti-Th-U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along deformation-related fast-diffusion pathways, such as dislocations and low-angle (<5°) boundaries. These results indicate chemical exchange between zircon and the surrounding matrix and show that Ti-in-zircon thermometry and U-Pb geochronology from deformed zircon may not yield information relating to the conditions and timing of primary crystallisation. |
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| format | Journal Article |
| id | curtin-20.500.11937-40878 |
| institution | Curtin University Malaysia |
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| last_indexed | 2025-11-14T09:05:03Z |
| publishDate | 2011 |
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| spelling | curtin-20.500.11937-408782017-09-13T15:57:39Z Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry Timms, Nicholas Eric Kinny, Peter Reddy, Steven Evans, Katy Clark, Chris Healy, David SHRIMP Siberia Xenolith Electron backscatter diffraction Granulite A zircon grain in an orthopyroxene-garnet-phlogopite-zircon-rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal-plastic deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U-Pb ages from more deformed zones (mean age of 1799 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 65 Ma, n = 7), and indicate that open system behaviour of Ti-Th-U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along deformation-related fast-diffusion pathways, such as dislocations and low-angle (<5°) boundaries. These results indicate chemical exchange between zircon and the surrounding matrix and show that Ti-in-zircon thermometry and U-Pb geochronology from deformed zircon may not yield information relating to the conditions and timing of primary crystallisation. 2011 Journal Article http://hdl.handle.net/20.500.11937/40878 10.1016/j.chemgeo.2010.10.005 Elsevier Science BV restricted |
| spellingShingle | SHRIMP Siberia Xenolith Electron backscatter diffraction Granulite Timms, Nicholas Eric Kinny, Peter Reddy, Steven Evans, Katy Clark, Chris Healy, David Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title | Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title_full | Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title_fullStr | Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title_full_unstemmed | Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title_short | Relationship among titanium, rare earth elements, U-Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry |
| title_sort | relationship among titanium, rare earth elements, u-pb ages and deformation microstructures in zircon: implications for ti-in-zircon thermometry |
| topic | SHRIMP Siberia Xenolith Electron backscatter diffraction Granulite |
| url | http://hdl.handle.net/20.500.11937/40878 |