A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia
© 2019 Elsevier B.V. The Fraser Zone is a major lithotectonic domain of the Albany–Fraser Orogen, Western Australia, which records Proterozoic modification of the margin of the Archean Yilgarn Craton. The Fraser Zone is volumetrically dominated by gabbroic rocks and their metamorphosed equivalents....
| Main Authors: | , , , , , , , , |
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| Format: | Journal Article |
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Elsevier BV
2019
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| Online Access: | http://hdl.handle.net/20.500.11937/74535 |
| _version_ | 1848763302237175808 |
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| author | Glasson, K. Johnson, Tim Kirkland, Chris Gardiner, Nicholas Clark, Christopher Blereau, E. Hartnady, M. Spaggiari, C. Smithies, H. |
| author_facet | Glasson, K. Johnson, Tim Kirkland, Chris Gardiner, Nicholas Clark, Christopher Blereau, E. Hartnady, M. Spaggiari, C. Smithies, H. |
| author_sort | Glasson, K. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | © 2019 Elsevier B.V. The Fraser Zone is a major lithotectonic domain of the Albany–Fraser Orogen, Western Australia, which records Proterozoic modification of the margin of the Archean Yilgarn Craton. The Fraser Zone is volumetrically dominated by gabbroic rocks and their metamorphosed equivalents. However, little is known of the pressure–temperature–time (P–T–t) history or the geodynamic setting of these mafic rocks. When considered within the context of existing P–T constraints from spatially-associated metapelitic rocks, modelled phase equilibria suggest that both the unmetamorphosed gabbros and the granulite facies metagabbroic rocks equilibrated at 950–900 °C and ~7 kbar, interpreted to record the conditions of magmatic crystallisation and peak metamorphism, respectively. These data support the view that mafic magmatism was the thermal driver for high-T, low-P granulite facies metamorphism. The absence of garnet from the metagabbroic rocks, and the lack of evidence for its former presence (i.e., as inclusions), argues that, during metamorphism, the rocks never reached pressures above those they attained at the thermal peak. Coronæ of zircon around ilmenite in the magmatic rocks reflect a local supply of Zr as it exsolved from ilmenite, permitting earlier growth of zircon around ilmenite than elsewhere during melt crystallisation. U–Pb dating of coronal zircon (1315 ± 5 Ma) and a discrete magmatic zircon grain isolated from ilmenite (1296 ± 5 Ma) constrain the duration of magmatic crystallisation between ca. 10 and 30 Ma. Zircon in a metamorphosed gabbro constrains the timing of granulite facies metamorphism to 1293 ± 6 Ma, synchronous with final crystallisation of the mafic magmas. Based on the implied metamorphic evolution of these rocks and that of the surrounding supracrustal package, along with existing isotopic and geochemical data, we suggest the Fraser Zone probably formed in a backarc, or perhaps an intracontinental rift setting, and records successive emplacement of gabbroic rocks into a thick, sediment-filled basin. The older gabbroic rocks record hydration and reaction with the devolatilising and/or partially molten metasedimentary rocks into which they were emplaced. Subsequent granulite facies metamorphism of these hydrated rocks was driven by the heat provided by the intrusion of younger mafic magmas. |
| first_indexed | 2025-11-14T11:01:18Z |
| format | Journal Article |
| id | curtin-20.500.11937-74535 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T11:01:18Z |
| publishDate | 2019 |
| publisher | Elsevier BV |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-745352019-02-19T05:36:19Z A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia Glasson, K. Johnson, Tim Kirkland, Chris Gardiner, Nicholas Clark, Christopher Blereau, E. Hartnady, M. Spaggiari, C. Smithies, H. © 2019 Elsevier B.V. The Fraser Zone is a major lithotectonic domain of the Albany–Fraser Orogen, Western Australia, which records Proterozoic modification of the margin of the Archean Yilgarn Craton. The Fraser Zone is volumetrically dominated by gabbroic rocks and their metamorphosed equivalents. However, little is known of the pressure–temperature–time (P–T–t) history or the geodynamic setting of these mafic rocks. When considered within the context of existing P–T constraints from spatially-associated metapelitic rocks, modelled phase equilibria suggest that both the unmetamorphosed gabbros and the granulite facies metagabbroic rocks equilibrated at 950–900 °C and ~7 kbar, interpreted to record the conditions of magmatic crystallisation and peak metamorphism, respectively. These data support the view that mafic magmatism was the thermal driver for high-T, low-P granulite facies metamorphism. The absence of garnet from the metagabbroic rocks, and the lack of evidence for its former presence (i.e., as inclusions), argues that, during metamorphism, the rocks never reached pressures above those they attained at the thermal peak. Coronæ of zircon around ilmenite in the magmatic rocks reflect a local supply of Zr as it exsolved from ilmenite, permitting earlier growth of zircon around ilmenite than elsewhere during melt crystallisation. U–Pb dating of coronal zircon (1315 ± 5 Ma) and a discrete magmatic zircon grain isolated from ilmenite (1296 ± 5 Ma) constrain the duration of magmatic crystallisation between ca. 10 and 30 Ma. Zircon in a metamorphosed gabbro constrains the timing of granulite facies metamorphism to 1293 ± 6 Ma, synchronous with final crystallisation of the mafic magmas. Based on the implied metamorphic evolution of these rocks and that of the surrounding supracrustal package, along with existing isotopic and geochemical data, we suggest the Fraser Zone probably formed in a backarc, or perhaps an intracontinental rift setting, and records successive emplacement of gabbroic rocks into a thick, sediment-filled basin. The older gabbroic rocks record hydration and reaction with the devolatilising and/or partially molten metasedimentary rocks into which they were emplaced. Subsequent granulite facies metamorphism of these hydrated rocks was driven by the heat provided by the intrusion of younger mafic magmas. 2019 Journal Article http://hdl.handle.net/20.500.11937/74535 10.1016/j.precamres.2019.01.011 Elsevier BV restricted |
| spellingShingle | Glasson, K. Johnson, Tim Kirkland, Chris Gardiner, Nicholas Clark, Christopher Blereau, E. Hartnady, M. Spaggiari, C. Smithies, H. A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title | A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title_full | A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title_fullStr | A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title_full_unstemmed | A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title_short | A window into an ancient backarc? The magmatic and metamorphic history of the Fraser Zone, Western Australia |
| title_sort | window into an ancient backarc? the magmatic and metamorphic history of the fraser zone, western australia |
| url | http://hdl.handle.net/20.500.11937/74535 |