THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH)
The geochemical and isotopic data were obtained for gneisses of the Kola Series, Baltic Shield. They are metamorphosed in granulite facies and interpreted according to the igneous nature of zircons and gneisses. The biotitic and garnet-biotitic gneisses are paralleled to the rocks of TTG association...
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| Language: | English |
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Karelian Research Centre of the Russian Academy of Sciences
2016-10-01
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| Series: | Transactions of the Karelian Research Centre of the Russian Academy of Sciences |
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| Online Access: | http://journals.krc.karelia.ru/index.php/precambrian/article/view/359 |
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| author | Татьяна Анатольевна Мыскова Раиса Ивановна Милькевич Tatiana Myskova Raisa Milkevich |
| author_facet | Татьяна Анатольевна Мыскова Раиса Ивановна Милькевич Tatiana Myskova Raisa Milkevich |
| author_sort | Татьяна Анатольевна Мыскова |
| collection | DOAJ |
| description | The geochemical and isotopic data were obtained for gneisses of the Kola Series, Baltic Shield. They are metamorphosed in granulite facies and interpreted according to the igneous nature of zircons and gneisses. The biotitic and garnet-biotitic gneisses are paralleled to the rocks of TTG associations in terms of the structure of correlation between the main elements. Sil ± Crd-Grt-Bt gneisses are formed on Grt-Bt gneisses as a result of blastomylonitization and partial melting. U-Pb zircon ages (SHRIMP-II) were determined for both gneiss species. All analytical points of magmatic zircons in the concordia diagram for Grt-Bt gneisses form a continuous trend extended in concordia in the range of 2909 ± 8 – 2732 ± 13 Ma. It is interpreted as the result of lead loss from magmatic zircons during the slow cooling of tonalite in the lower crust. Minimal age of magmatism and early granulitic metamorphism estimated by most ancient zircon is 2.9 Ga. The time of manifestation of younger granulite metamorphism determined by newly-formed zircon shells from Crd-Sil-Grt-Bt gneiss corresponds to the interval 2707 ± 9 – 2656 ± 8 Ma. Part of the zircon from Crd-Sil-Grt-Bt gneiss is profoundly altered crystals with a discordant age of 2740 ± 6 – 2639 ± 9 Ma, which is similar to that of metamorphic shells, suggesting an event happened at that time which disrupted the crystalline grid and caused the loss of radiogenic lead. Three ancient zircons with a maximum age of 3461 ± 5 MA are interpreted as captured zircons, which indicate the presence of continental crust at this point in the northern part of the Baltic Shield. |
| first_indexed | 2024-12-12T03:17:38Z |
| format | Article |
| id | doaj.art-23d4a6f638bc4438a8a2c736c135c930 |
| institution | Directory Open Access Journal |
| issn | 1997-3217 2312-4504 |
| language | English |
| last_indexed | 2024-12-12T03:17:38Z |
| publishDate | 2016-10-01 |
| publisher | Karelian Research Centre of the Russian Academy of Sciences |
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| series | Transactions of the Karelian Research Centre of the Russian Academy of Sciences |
| spelling | doaj.art-23d4a6f638bc4438a8a2c736c135c9302022-12-22T00:40:15ZengKarelian Research Centre of the Russian Academy of SciencesTransactions of the Karelian Research Centre of the Russian Academy of Sciences1997-32172312-45042016-10-01010346210.17076/geo359305THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH)Татьяна Анатольевна Мыскова0Раиса Ивановна МилькевичTatiana MyskovaRaisa MilkevichИнститут геологии и геохронологии РАНThe geochemical and isotopic data were obtained for gneisses of the Kola Series, Baltic Shield. They are metamorphosed in granulite facies and interpreted according to the igneous nature of zircons and gneisses. The biotitic and garnet-biotitic gneisses are paralleled to the rocks of TTG associations in terms of the structure of correlation between the main elements. Sil ± Crd-Grt-Bt gneisses are formed on Grt-Bt gneisses as a result of blastomylonitization and partial melting. U-Pb zircon ages (SHRIMP-II) were determined for both gneiss species. All analytical points of magmatic zircons in the concordia diagram for Grt-Bt gneisses form a continuous trend extended in concordia in the range of 2909 ± 8 – 2732 ± 13 Ma. It is interpreted as the result of lead loss from magmatic zircons during the slow cooling of tonalite in the lower crust. Minimal age of magmatism and early granulitic metamorphism estimated by most ancient zircon is 2.9 Ga. The time of manifestation of younger granulite metamorphism determined by newly-formed zircon shells from Crd-Sil-Grt-Bt gneiss corresponds to the interval 2707 ± 9 – 2656 ± 8 Ma. Part of the zircon from Crd-Sil-Grt-Bt gneiss is profoundly altered crystals with a discordant age of 2740 ± 6 – 2639 ± 9 Ma, which is similar to that of metamorphic shells, suggesting an event happened at that time which disrupted the crystalline grid and caused the loss of radiogenic lead. Three ancient zircons with a maximum age of 3461 ± 5 MA are interpreted as captured zircons, which indicate the presence of continental crust at this point in the northern part of the Baltic Shield.http://journals.krc.karelia.ru/index.php/precambrian/article/view/359балтийский щитприрода архейских гнейсовu-pb геохронологияциркон |
| spellingShingle | Татьяна Анатольевна Мыскова Раиса Ивановна Милькевич Tatiana Myskova Raisa Milkevich THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) Transactions of the Karelian Research Centre of the Russian Academy of Sciences балтийский щит природа архейских гнейсов u-pb геохронология циркон |
| title | THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) |
| title_full | THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) |
| title_fullStr | THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) |
| title_full_unstemmed | THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) |
| title_short | THE ALUMINOUS GNEISSES OF KOLA SERIES, BALTIC SHIELD (GEOCHEMISTRY, NATURE AND AGE OF PROTOLITH) |
| title_sort | aluminous gneisses of kola series baltic shield geochemistry nature and age of protolith |
| topic | балтийский щит природа архейских гнейсов u-pb геохронология циркон |
| url | http://journals.krc.karelia.ru/index.php/precambrian/article/view/359 |
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