Origin of the Belomorian Chupa Gneiss in the Light of New Lithogeochemical Data |
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Authors: | Myskova T A Mil'kevich R I L'vov A B Miller Yu V |
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Institution: | (1) Institute of Precambrian Geology and Geochronology (IGGD), Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia |
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Abstract: | The stratotype Chupa Sequence, which makes up the synonymous tectonic nappe and is a member of oldest (Late Archean) rocks in the Belomorian Mobile Belt, is scrutinized. The nappe is mainly composed of the migmatized, coarse-grained garnet–biotite gneiss with kyanite. Relic formations are represented by lenses of the fine-grained (possibly primary) garnet–biotite gneiss. Fine-grained gneisses generally represent primary sedimentary formations, while metadacites are rare. The kyanite-bearing gneiss is presumably a restitic rock produced by migmatization. Chupa metasediments are represented by immature (low-differentiated) metagraywackes and are akin to metaterrigenous rocks from Late Archean greenstone belts of Karelia (Kostomuksha) and Canada (Quetico). The provenance of metasediments comprises the following three components: tonalite (dacite) 70%, mafic rocks 20%, and ultramafic rocks 10%. The Chupa metagraywacke presumably deposited in a fore-arc basin. |
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