Remanent Magnetization in the Archaean Basement and Cutting

• Main Authors: Diabase Dykes In Finl, Ian Shield, K. J. Neuvonen, L. J. Pesonen, H. Pietarinen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1996
• Subjects: Fennoscandian
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.502.7792; http://www.geophysica.fi/pdf/geophysica_1997_33_1_111_neuvonen.pdf

New palaeomagnetic results on basement rocks and cutting diabases from Archaean terranes in Finland (Fennoscandian Shield) are presented. The terranes studied are Varpaisjärvi in central Finland, Eno-Ilomantsi in eastern Finland and Kuhmo-Suomussalmi in northeastern Finland. The Varpaisjärvi results are from five Archaean blocks showing variation in tectonic styles, orientation of dyke swarms and magnetic anomaly patterns. The palaeomagnetic data are treated with respect to their source blocks to seek differences in magnetization directions between blocks caused by tectonism or age. The analysis is based on original results of one of the authors (K.J. Neuvonen), where the demagnetization data were submitted to an optimum cleaning strategy without multicomponent analysis. Three main magnetization directions were isolated: (i) Archaean magnetization in the basement rocks (component Ar), (ii) a direction corresponding to the cutting (presumably Jatulian) diabase dykes and their baked host rocks (component Ja), and (iii) the Svecofennian direction observed in some basement rocks, dykes and baked contacts (component Sf). Of these, the Archaean directions most likely reflect the last metamorphic cooling, which took place 2680–2630 Ma ago in the Varpaisjärvi