Intrusive age and geochemistry of the Kebne Dyke Complex in the Seve Nappe Complex, Kebnekaise Massif, arctic Sweden Caledonides

Abstract

The Seve Nappe Complex of the Scandinavian Caledonides is predominately metamorphosed rift-related igneous and sedimentary rocks formed during Rodinia breakup in the Neoproterozoic. The Kebne Dyke Complex of the Kebnekaise Massif, arctic Sweden, is one such unit within the Seve Nappe Complex and is mostly composed of dolerite dykes metamorphosed and thrust onto Baltica during the Caledonian orogeny. Structurally adjacent to the dyke complex are geochemically similar amphibolites that have a common origin as the metadolerite dykes. Collectively, these rocks have transitional mid-ocean ridge basalt geochemistry similar to correlative Seve Nappe Complex rocks to the north (Indre Troms dykes) and south (Sarek Dyke Swarm). U–Pb single-crystal chemical abrasion–thermal ionization mass spectrometry of zircon from a metagabbro and a metagranitoid, showing co-mingling magmatic textures with the metadolerite, produced 11 concordant analyses with ²⁰⁶Pb/²³⁸U ages ranging from 608 to 596 Ma, which includes the magmatic age of the dyke complex. These results support the idea that the Kebne Dyke Complex, Sarek Dyke Swarm and Indre Troms dykes constitute the tholeiitic continent–ocean transition subdivision within the Seve Nappe Complex. However, the Kebne Dyke Complex differs from the Sarek Dyke Swarm and Indre Troms dykes as it is the least enriched among these, nearly lacks rift-related metasedimentary rocks, and may be younger than the Sarek Dyke Swarm by up to 14 Myr.

Keywords::

• Kebne Dyke Complex
• Seve Nappe Complex
• Kebnekaise Massif
• Scandinavian Caledonides
• igneous geochemistry
• U–Pb single-crystal zircon geochronology

Acknowledgements

This contribution stemmed from Masters research done by S.A. Figg at University of Northern Colorado (UNCO), advised by G.B. Baird. Field accommodations were provided by the Tarfala Research Station, operated by Stockholm University. Field logistical collaborations with Keith Brugger and Tysha Pankratz (University of Minnesota-Morris) are gratefully acknowledged and made the research possible. Keith Brugger is also thanked for providing Fig. 3(H). This research was supported by multiple UNCO Provost Fund for Faculty Scholarship and Professional Development Research Grants, an UNCO Summer Support Initiative grant and the UNCO Department of Earth and Atmospheric Sciences. The UNCO SEM was purchased through NSF grant CHE-0959879. Geochemical plots were produced with the aid of Igpet 2013. Thorough reviews by F. Corfu and O. Svenningsen, and editorial comments by M. Ripa, are gratefully acknowledged and significantly improved the manuscript.