Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Geological Magazine

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by ROBERTS, R. J. Articles by RAMSAY, D. M. Search for Related Content GeoRef GeoRef Citation

Short-lived mafic magmatism at 560–570 Ma in the northern Norwegian Caledonides: U–Pb zircon ages from the Seiland Igneous Province

R. J. ROBERTS^*,, F. CORFU, T. H. TORSVIK, L. D. ASHWAL^* and D. M. RAMSAY^¶

^* School of Geosciences, Private Bag 3, University of the Witwatersrand, Johannesburg 2050, Republic of South Africa
Department of Geology, University of Oslo, Oslo, Norway
Geodynamic Centre, Geological Survey of Norway, Leiv Erikssonsvei 39, N-7491 Trondheim, Norway; and Institute for Petroleum Technology and Applied Geophysics, NTNU, N-7491 NTNU, Norway
^¶ 27 Marlee Road, Dundee, Scotland, UK

Author for correspondence: james{at}armoury.co.za

The Seiland Igneous Province (SIP) of northern Norway comprises a suite of mainly gabbroic plutons, with subordinate ultramafic, syenitic and felsic intrusions. Several intrusions from the Seiland Igneous Province have been dated by ID-TIMS U–Pb zircon and monazite analyses. The Hasvik Gabbro on the island of Sørøy, previously assigned an age of 700 ± 33 Ma by Sm–Nd, yields a U–Pb zircon age of 562 ± 6 Ma, within error of the Storelv Gabbro (569 ± 5 Ma) and a diorite associated with the Breivikbotn Gabbro (571 ± 4 Ma). Various intrusions on the Øksfjord peninsula give nearly identical ages of 565 ± 9 Ma (gabbro), 566 ± 4 Ma (monzonite), 565 ± 5 Ma (monzodiorite), 570 ± 9 Ma (norite), and 566 ± 1 Ma (orthopyroxenite). These ages overlap with those from Sørøy, and define a single and short-lived period of gabbroic (to felsic) magmatism for the region between 570 and 560 Ma, pre-dating a subordinate episode of alkalic magmatism at 530–520 Ma. The U–Pb ages contradict the previous geochronological interpretation for the Finnmark area, which implied a period of 250 m.y. for the emplacement of the SIP intrusions. The new age data also clearly distinguish the Seiland intrusions, emplaced into the Sørøy Group metasediments of the Kalak Nappe Complex, from several older granitic intrusions (c. 850 to 600 Ma) that cut the Sørøy Group farther east and south. The coincident ages of the different Seiland intrusive bodies also contradict the previous structural model for the area, which posits that the different gabbro bodies were emplaced at intervals, with compressional deformation affecting the gabbros between periods of intrusion. The short time span between the main plutonic phases strongly suggests that the mechanism for the emplacement of mafic magma operated in a single, probably extensional, tectonic regime. The mafic intrusions were later deformed and metamorphosed to at least amphibolite facies, most likely by the Scandian (420 Ma) phase of the Caledonian Orogeny.

Key Words: Seiland • age • magmatism • zircon • Caledonides

This article has been cited by other articles:

				C. L. Kirkland, J. S. Daly, E. A. Eide, and M. J. Whitehouse Tectonic evolution of the Arctic Norwegian Caledonides from a texturally- and structurally-constrained multi-isotopic (Ar-Ar, Rb-Sr, Sm-Nd, U-Pb) study Am J Sci, February 1, 2007; 307(2): 459 - 526. [Abstract] [Full Text] [PDF]