Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria
In an attempt to better constrain the timing of Variscan HP-HT metamorphism in the SE Bohemian Massif we have dated zoned zircons from a garnet-kyanite granulite of granitic composition from the Dunkelsteiner Wald Massif, Lower Austria, by means of sensitive high-resolution ion microprobe (SHRIMP) t...
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| Format: | Journal Article |
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Springer
2011
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| Online Access: | http://hdl.handle.net/20.500.11937/13118 |
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| author | Friedl, G. Cooke, R. Finger, F. McNaughton, Neal Fletcher, Ian |
| author_facet | Friedl, G. Cooke, R. Finger, F. McNaughton, Neal Fletcher, Ian |
| author_sort | Friedl, G. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | In an attempt to better constrain the timing of Variscan HP-HT metamorphism in the SE Bohemian Massif we have dated zoned zircons from a garnet-kyanite granulite of granitic composition from the Dunkelsteiner Wald Massif, Lower Austria, by means of sensitive high-resolution ion microprobe (SHRIMP) technique. In order to combine isotopic information with crystal growth textures, CL and BSE images were systematically taken from the dated zircons. A characteristic threefold concentric zoning was found in many zircons. This involves pre-Variscan protolithic cores followed by two distinct metamorphic/anatectic overgrowth shells of Variscan age. The inner overgrowth shell is characterized by a weak CL but bright BSE signal, and yields high contents of uranium (0.1 to 0.2 wt.%). A pooled U-Pb Concordia age for this zone is 342.0 ± 3.0 Ma (n = 11, MSWD = 0.12). The second, outer, overgrowth shell is always bright in the CL image, dark in the BSE image, and has generally low uranium contents (mostly <500 ppm). A pooled U-Pb Concordia age for this zone is 337.1 ± 2.7 Ma (n = 11, MSWD = 0.22). These results imply that the Variscan HT crystallisation history of the Moldanubian granulites took place over a period of a few million years and was not an extremely rapid subduction-exhumation process.SHRIMP measurements in the protolithic cores yield a cluster of (sub)concordant ages between ∼390 and 460 Ma and a few outliers at higher ages mostly represented by cores in cores. Core domains, which are large, homogeneous and with undisturbed igneous oscillatory zoning, yielded preferentially ages between 430 and 460 Ma. We therefore consider that granitic protolith formation took place at that time. The still older inner cores are interpreted as inherited into the granitic melt. |
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| format | Journal Article |
| id | curtin-20.500.11937-13118 |
| institution | Curtin University Malaysia |
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| last_indexed | 2025-11-14T07:02:15Z |
| publishDate | 2011 |
| publisher | Springer |
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| spelling | curtin-20.500.11937-131182017-09-13T16:07:47Z Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria Friedl, G. Cooke, R. Finger, F. McNaughton, Neal Fletcher, Ian Dunkelsteiner Wald Massif SHRIMP granitic protolith formation concentric zoning zircon Variscan CL U-Pb Concordia age In an attempt to better constrain the timing of Variscan HP-HT metamorphism in the SE Bohemian Massif we have dated zoned zircons from a garnet-kyanite granulite of granitic composition from the Dunkelsteiner Wald Massif, Lower Austria, by means of sensitive high-resolution ion microprobe (SHRIMP) technique. In order to combine isotopic information with crystal growth textures, CL and BSE images were systematically taken from the dated zircons. A characteristic threefold concentric zoning was found in many zircons. This involves pre-Variscan protolithic cores followed by two distinct metamorphic/anatectic overgrowth shells of Variscan age. The inner overgrowth shell is characterized by a weak CL but bright BSE signal, and yields high contents of uranium (0.1 to 0.2 wt.%). A pooled U-Pb Concordia age for this zone is 342.0 ± 3.0 Ma (n = 11, MSWD = 0.12). The second, outer, overgrowth shell is always bright in the CL image, dark in the BSE image, and has generally low uranium contents (mostly <500 ppm). A pooled U-Pb Concordia age for this zone is 337.1 ± 2.7 Ma (n = 11, MSWD = 0.22). These results imply that the Variscan HT crystallisation history of the Moldanubian granulites took place over a period of a few million years and was not an extremely rapid subduction-exhumation process.SHRIMP measurements in the protolithic cores yield a cluster of (sub)concordant ages between ∼390 and 460 Ma and a few outliers at higher ages mostly represented by cores in cores. Core domains, which are large, homogeneous and with undisturbed igneous oscillatory zoning, yielded preferentially ages between 430 and 460 Ma. We therefore consider that granitic protolith formation took place at that time. The still older inner cores are interpreted as inherited into the granitic melt. 2011 Journal Article http://hdl.handle.net/20.500.11937/13118 10.1007/s00710-011-0162-x Springer restricted |
| spellingShingle | Dunkelsteiner Wald Massif SHRIMP granitic protolith formation concentric zoning zircon Variscan CL U-Pb Concordia age Friedl, G. Cooke, R. Finger, F. McNaughton, Neal Fletcher, Ian Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title | Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title_full | Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title_fullStr | Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title_full_unstemmed | Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title_short | Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria |
| title_sort | timing of variscan hp-ht metamorphism in the moldanubian zone of the bohemian massif: u-pb shrimp dating on multiply zoned zircons from a granulite from the dunkelsteiner wald massif, lower austria |
| topic | Dunkelsteiner Wald Massif SHRIMP granitic protolith formation concentric zoning zircon Variscan CL U-Pb Concordia age |
| url | http://hdl.handle.net/20.500.11937/13118 |