The Late Archaean Mikkelvik alkaline stock (30x50 m) is located in the West Troms Basement Complex (WTBC), northern Norway, intruding a tonalite-trondhjemite-granodiorite (TTG) complex. U-Pb dating of titanite yielded an age of 2695±15 Ma. The stock is composed of a differentiated rock series including nepheline syenite (first and major magmatic phase), cancrinite syenite (minor dykes), and alkali (aegirine-augite) syenite (latest magmatic phase). The rocks are characterized by depletion in some HFS elements (Zr, Nb, Y), enrichment in some LIL elements (Sr, Ba) and strong REE fractionation. Geochemical data suggest that that the rocks developed from an OIB-like magma. Differentiation from alkali basalt was principally controlled by fractionation of pyroxene and amphibole. Isotopic data for Nd yield εNd(t) = 3.0 - 3.6, which is characteristic of depleted mantle, but with εSr(t) = 5 – 19 indicating some enrichment or crustal input. Among all known Archaean alkaline complexes, the Skjoldungen province (eastern Nain craton, Greenland) is most similar to the rocks studied here in terms of age, isotopic and geochemical signatures, indicating a similar geodynamic evolution of Greenland and WTBC in the Late Archaean.
Geology, age and geochemical constraints on the origin of the Late Archaean Mikkelvik alkaline stock, West Troms Basement Complex in Northern Norway