A Permian pole from Paleoproterozoic Gneisses of the Lofoten Islands, Norway??
Abstract
Paleoproterozoic rocks including paragneisses and Anorthosite-Mangerite-Charnockite-Granite suite rocks dominate the landscape in the southern Lofoten islands of Norway, sandwiched between the Scandinavian Caledonides to the east and off-shore Mesozoic basins to the west. Published geochronology on the AMCG suite and the metamorphism of the gneisses they intrude range from 1.9 to 1.8 Ga, suggesting tectonic activity in this area was coincident with the formation of the supercontinent Columbia. Rare eclogites of Lower Devonian age ( 400 Ma) indicate Caledonian activity in the region, when theses rocks were at greater than 15 kbars and 680°C. Twenty-seven sites were drilled into rocks from Moskenesøy and Flakstadøy, the southernmost Lofoten islands, to investigate their paleomagnetic character and possibly determine a Paleoproterozoic pole for Baltica. Magnetic susceptibility for the 27 sites averages 6.95 x 10-2 SI and NRM values average 2.01 A/m. Hysteresis properties indicate MD magnetite is the dominant iron-oxide present, but optical investigations and demagnetization studies show that high coercivity phases (hemo-ilmenite and ilmeno-hematite) are commonly present and control the stable remanence. Both normal and reversed polarities, nearly antipodal, are observed, with a mean direction of I = -49° and D= 210° (N = 18 sites) with a corresponding paleopole at 48°N, 152°E. The paleolatitude from this study of -30° places the current northwestern side of Baltica at low latitudes at the time of magnetization. The derived pole position is unlike any pole for Baltica in the Paleoproterozic or the early to mid Paleozoic. The pole is most similar to Baltica poles from mid Permian time ( 270 Ma), suggesting the remanence was not gained until well after the Caledonian orogeny. As the uplifted basement rocks are now exposed at the surface due to Mesozoic normal faulting, alternative explanations for the observed pole could include vertical and/or horizontal rotations during opening of the North Sea.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP31B1304B
- Keywords:
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- 0699 General or miscellaneous;
- ELECTROMAGNETICSDE: 1599 General or miscellaneous;
- GEOMAGNETISM AND PALEOMAGNETISM