Interpretation of the Proterozoic Kautokeino greenstone belt, Finnmark, Norway from combined geophysical and geological data

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Authors:Olesen, Odleiv; Sandstad, Jan Sverre
Author Affiliations:Primary:
Norges Geologiske Undersokelse, Trondheim, Norway
Volume Title:Bulletin - Norges Geologiske Undersokelse
Source:Bulletin - Norges Geologiske Undersokelse, Vol.425, p.41-64. Publisher: Universitetsforlaget, Trondheim - Oslo, Norway. ISSN: 0332-5768
Publication Date:1993
Note:In English. 90 refs. Color aeromagnetic map 1:250,000; Color gravity survey map 1:250,000; Color geologic map 1:250,000; Color shaded relief map 1:250,000; illus., incl. sect., 1 table, geol. sketch maps
Summary:Processed images of aeromagnetic, gravimetric and topographical data and geological maps combined with EM helicopter measurements, petrophysical data and digitised geological field observations have been used in a geological interpretation and structural analysis of the Kautokeino Greenstone Belt, KGB. The data were analysed with an image-processing system (geophysical data) and a geographic information system (geological data and interpretations). The bulk of the mafic volcanic rocks in the Kautokeino Greenstone Belt is situated within a NNW-SSE-trending, 35 km wide and up to 5-6 km deep trough which is thought to represent an Early Proterozoic rift deformed by strike-slip faulting along the Bothnian-Kvaenangen Fault Complex, BKFC. The margins of the Alta-Kautokeino Rift, AKR, can be outlined from the geophysical data. The Ciegnaljakka-Boaganjavri Lineament and the Soadnjujavri-Bajasjavri Fault are the main bordering fault zones and are continuous along the entire greenstone belt. The supracrustals between these two zones are continuous to great depth (5-6 km) and the contacts along these bordering zones are steeply dipping. Gravity interpretations show that the outer amphibolite-facies rocks are just as deep as the central greenschist-facies unit. Results of the present study suggest that the amphibolite-facies volcano-sedimentary rocks situated along the flanks of the KGB should also be included in the rift. The mudstones and limestones in the Bikkacakka Formation may have been formed during thermal subsidence as a result of cooling of upwelled asthenosphere after a phase of rifting. The above-lying deep and narrow Caravarri Formation contains abundant coarse-grained sandstones and conglomerates derived from a granitic source. We believe the Caravarri Formation to have been the result of late-stage uplift of the margins, subsequent erosion of the exposed basement, and deposition of the sediments in deep internal basins. Strike-slip movements may be incorporated in this model. Large-scale sinistral displacement along the BKFC embraced the AKR which was already a zone of weakness in the Karelian continental block. This strike-slip movement may have allowed the Caravarri Formation to form in a pull-apart basin within the rift. The 230 km long Mierujavri-Svaerholt Fault Zone, MSFZ, is the main fault zone which separates the flat-lying volcanosedimentary sequences in the Masi area from the Jergol Gneiss Complex to the southeast. The MSFZ extends from Mierujavri 30 km north of Kautokeino in a northeasterly direction through Masi, Iesjavri and Lakselv and then beneath the Caledonian nappes on the Svaerholt Peninsula. A system of duplexes can be delineated along the MSFZ from the geophysical images. An extension of the MSFZ can be found to the southwest into northern Sweden. An apparent sinistral offset of the MSFZ can be observed along the margins of the BKFC.
Subjects:Aeromagnetic maps; Airborne methods; Bedrock; Digital terrain models; Electromagnetic methods; Fault zones; Faults; Geographic information systems; Geologic maps; Geophysical methods; Geophysical surveys; Gravity field; Gravity methods; Gravity survey maps; Greenstone belts; Igneous rocks; Information systems; Interpretation; Intrusions; Magnetic field; Magnetic methods; Magnetic properties; Magnetic susceptibility; Maps; Metamorphic belts; Metamorphic rocks; Paleomagnetism; Precambrian; Proterozoic; Relief; Sedimentary rocks; Shaded relief maps; Spectra; Surveys; Tectonic elements; Tectonics; Upper Precambrian; Europe; Finnmark Norway; Norway; Scandinavia; Western Europe; Kautokeino greenstone belt; Color aeromagnetic map; Color gravity survey map; Color geologic map; Color shaded relief map
Coordinates:N683000 N693000 E0240000 E0220000
Abstract Numbers:95M/1099
Record ID:2008098077
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute.
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