GEOCHEMISTRY AND INTRUSIVE AGE OF THE KEBNE DYKE COMPLEX IN THE KEBNEKAISE MASSIF, NORTHERN SWEDISH CALEDONIDES: COMPARISON OF THE THOLEIITIC CONTINENTAL-OCEANIC TRANSITION ROCKS IN THE SEVE-KALAK SUPERTERRANE

The Seve-Kalak Superterrane (SKS) is a ~1000 km long collection of Iapetus seafloor and rift related rocks now found in the allochthonous nappe complexes of the Scandinavian Caledonides. The SKS is thought have formed by the breakup of the supercontinent Rodinia and was subsequently metamorphosed and thrust ~400-600 km onto the Baltic Shield during the Caledonian orogeny. One subdivision of the SKS is the tholeiitic mafic igneous rocks of the continental-oceanic transition (TCO) and includes the meta-dolerite dykes found in the Sarek, Kebnekaise, Abisko, and Indre Troms Mts. of northern Sweden and Norway. Bulk rock chemical analysis of the meta-dolerite dykes of the Kebne Dyke Complex (KDC) in the Kebnekaise massif, complemented by U-Pb zircon geochronology, provides a dataset that helps establish the relationship of the KDC to other TCO rocks.

Geochemical results indicate that the KDC is comprised of tholeiitic mafic rocks based on alkali vs. silica and AFM diagrams. On multiple ternary discrimination diagrams, the KDC plots predominately as MORB. However, on normalized REE and multi-element diagrams, the KDC shows minor enrichment of the LREEs and the most incompatible elements compared to N-MORB, such that the KDC is best characterized as a T-MORB. Preliminary CA-TIMS U-Pb geochronology of zircons from a meta-gabbro and a meta-granitoid, both displaying magma-mingling textures with the meta-dolerite dykes, establishes a current best estimate of 604±2 Ma for KDC formation.

Comparison between this data and similar data from the Sarek and Indre Troms areas published by others show nearly identical geochemistry among the TCO rocks except that the Sarek and Indre Troms areas are slightly more enriched than the KDC. The ca. 604 Ma age indicates the KDC is 1-7 Myr younger than the Sarek TCO rocks. The KDC also has a conspicuous lack of meta-sediments serving as the country rock to the dolerite dykes compared to other TCO rocks. These outlined differences suggest the KDC represents originally a slightly more offshore slice of Iapetus seafloor as compared to other TCO members.