Geology of the southern part of the Kautokeino Greenstone Belt: Rb-Sr geochronology and geochemistry of associated gneisses and late intrusions.

• Main Authors: Olsen, Karl Inge, Nilsen, Kjell S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1985
• Subjects: DATERING; GRANITT; GRØNNSTEIN; OMDANNING; PREKAMBRIUM; Kautokeino; North Finland
• Online Access: https://hdl.handle.net/11250/2674243

The southern part of the Kautokeino Greenstone Belt is divided into four volcanic formations separated by sedimentary units. The formation represent a development from Archaean komatiitic sequences to Middle Proterozoic possible rift-forming environemnts. The earliest volcanism is represented by basaltic komatiitic enclaves within the eastern gneiss complex, and may be equivalent to parts of the lowermost formation within the greenstone belt. The latter consists of up to 50% basaltic to peridotitic komatiites (12-30% MgO) and was probably deposited after the formation of the gneiss complex. The tonalitic-trondhjemitic gneisses arc dated to 3.0+-0.2 b.y. and represent primary magmas reulting from the crust-forming events at that time. They are similar in age and composition to gneisses in East and North Finland. The late plutonic complexes are ca. 1700 m.y.old and may be the Middle Proterozoic counterparts to the Archaean gneisses. Regional metamorphism within the belt reached middle to high amphibolite facies and occurred ca. 1950 m.y. ago on the basis of Rb-Sr radiometric dating on metasediments and amphibolites. Granitic gneisses southwest of the main greenstone belt are very uniform geochemically and represent products of differentiation. Widespread and intensive brecciation, shearing and carbonatization are later than the main deformation and metamorphism, and may be associated with faulting and block movements in connection with possible rift tectonics. 36186