Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

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Evolution of Migmatitic Granulite Complexes: Implications From Lapland Granulite Belt, Part I: Metamorphic Geology


Affiliations
1 Department of Geoscience, University of Oulu, P 0 Box 3000 FI-90014, Finland
2 Geological Survey of Finland, P O Box 1237, FI - 70211, KUOPIO, Finland
3 Geological Survey of Finland, P 0 Box, FI - 0215 1, Espoo, Finland
 

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The palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Proterozoic terranes in the NE part of the Fennoscandian Shield concuriently with th e accretion of Svecofennian arc complexes at I 9 Ga The belt consists of aluminous migmatitic metagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly in to the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas This is supported by a structural and contact relations of metasediments and igneous rocks, and by the lack progressive metamorphic reaction textures in the igneous rock series The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quaratz assemblage at 750-850°C and 5-8 5 kbar which lead to formation of a restiti palaeosome and peraluminous granitic melt in metapelites Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pehtic rocks (650°C) undel the stability field of andalusite coexisting with potassium feldspar (2-3 kbar) Cooling was accompanied by the crystalllzation of the neosomes, often carrying aluminium-rich phases Post-metamorphic duplexing of the LGB IS clearly seen in the distribution of calculated PT conditions.
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  • Evolution of Migmatitic Granulite Complexes: Implications From Lapland Granulite Belt, Part I: Metamorphic Geology

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Authors

Pekka Tuisku
Department of Geoscience, University of Oulu, P 0 Box 3000 FI-90014, Finland
Perttu Mikkola
Geological Survey of Finland, P O Box 1237, FI - 70211, KUOPIO, Finland
Hannu Huhma
Geological Survey of Finland, P 0 Box, FI - 0215 1, Espoo, Finland

Abstract


The palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Proterozoic terranes in the NE part of the Fennoscandian Shield concuriently with th e accretion of Svecofennian arc complexes at I 9 Ga The belt consists of aluminous migmatitic metagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly in to the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas This is supported by a structural and contact relations of metasediments and igneous rocks, and by the lack progressive metamorphic reaction textures in the igneous rock series The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quaratz assemblage at 750-850°C and 5-8 5 kbar which lead to formation of a restiti palaeosome and peraluminous granitic melt in metapelites Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pehtic rocks (650°C) undel the stability field of andalusite coexisting with potassium feldspar (2-3 kbar) Cooling was accompanied by the crystalllzation of the neosomes, often carrying aluminium-rich phases Post-metamorphic duplexing of the LGB IS clearly seen in the distribution of calculated PT conditions.