Evolution of Migmatitic Granulite Complexes: Implications from Lapland Granulite Belt, Part I: Metamorphic geology

• Main Authors: Pekka Tuisku, Perttu Mikkola, Hannu Huhma
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Key words; granulites; Lapland Granulite Belt; migmatites; metasedimentary rocks; metapelite; enderbite; mineralogy; metamorphism; P-T conditions; Paleoproterozoic; Lap- land Province; Finland *Corresponding author; Fennoscandian; Lapland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.494.8841; http://www.geologinenseura.fi/bulletin/Volume78/tuisku.pdf

The Palaeoproterozoic Lapland granulite belt was juxtaposed between Archaean and Prot-erozoic terrains in the NE part of the Fennoscandian Shield concurrently with the accretion of Svecofennian arc complexes at ~1.9 Ga. The belt consists mainly of aluminous migmatitic metagreywackes. Abundant noritic to enderbitic magmas were intruded concordantly into the metasediments and were probably an important heat source for metamorphism, which took place during the crystallization of the magmas. This is supported by structural and con-tact relations of metasediments and igneous rocks, and by the lack progressive metamor-phic reaction textures in the igneous rock series. The peak of metamorphism took place above the dehydration melting temperature of the biotite-sillimanite-plagioclase-quartz as-semblage at 750−850°C and 5−8.5 kbar which lead to formation of a restitic palaeosome and peraluminous granitic melt in metapelites. Subsequently, the rocks were decompressed and cooled below the wet melting temperature of pelitic rocks (650°C) under the stability fi eld of andalusite coexisting with potassium feldspar (2−3 kbar). Cooling was accompanied by the crystallization of the neosomes, often carrying aluminium-rich phases. Postmetamor-phic duplexing of the LGB is clearly seen in the distribution of calculated PT conditions.