Cambrian sediments and Proterozoic granites in the Dividalen-Tornetrask area, northern Scandinavia: Palaeomagnetism and U-Pb geochronology
Titel:
Cambrian sediments and Proterozoic granites in the Dividalen-Tornetrask area, northern Scandinavia: Palaeomagnetism and U-Pb geochronology
Auteur:
Rehnstrom, Emma F. Torsvik, Trond H.
Verschenen in:
GFF
Paginering:
Jaargang 125 (2003) nr. 3 pagina's 131-138
Jaar:
2003-09-01
Inhoud:
New palaeomagnetic data from the autochthonous Early Cambrian Dividal Group (northern Scandinavia) confirm earlier findings, and a refined palaeomagnetic pole of 58.4d`N and 122.5d`E, places Baltica at intermediate southerly latitudes at ∼535 Ma. Palaeomagnetic data from the immediately underlying granitic basement (pole: 9.8d`N, 226.7d`E) differ markedly from the Dividal sediments. The result of this fieldtest increases the palaeomagnetic reliability of the Dividal Group results. We dated the granitic basement in the eastern part of the Tornetrask area (corresponding to our palaeomagnetic site) to 1786±4 Ma (U-Pb zircon and titanite), whilst deformed allochthonous granites west of lake Tornetrask are slightly older (1800±4 Ma; U-Pb zircon). These ages are compatible with autochthonous basement ages to the east of the study area, but also with ages from basement windows to the west. Preliminary palaeomagnetic data from the 1786±4 Ma granitic basement are clearly pre-Phanerozoic in origin, and comparable and concordant zircon and titanite ages may hint that the magnetisation could be primary. However, the palaeomagnetic pole does not match contemporaneous poles from Baltica, which suggest a tectonic explanation (no palaeohorizontal control), a problem of secular variation (only one site) or a younger but pre-Phanerozoic remagnetisation event, which did not affect the U-Pb system in zircon and titanite.
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