Dilational mafic dykes intruded during and after the second phase of early Caledonian deformation in the Seiland province were emplaced into complex fracture systems. Despite subsequent metamorphism, some dykes retain chilled margins, internal boundaries reflecting several magmatic pulses, central concentrations of phenocrysts, ocelli, and ultramafic nodules. Olivine, aluminous clinopyroxene, labradoritic plagioclase, nickeliferous pyrrhotite, magnetite-hercynite ss., ferri-ilmenite, the absence of Ca-poor pyroxene, and groundmass olivine in the freshest dykes indicate alkali olivine basalt affinities. The dykes have a mean major-element composition in the alkali picrite range, and the chemical variation is explained by accumulation of olivine and clinopyroxene. Na and K variations appear to be inherited from a pre-accumulation history. Mean Rb/Sr, K/Rb, K/Sr, and Y/Nb ratios correspond with common basalts, Ca/Sr is high and K, Nb, Zr, Rb, and the REE are positively correlated. Normalized REE patterns vary in absolute enrichment, but are light-REE enhanced. The primary magmas were generated by varying degrees of partial metting of an inhomogeneous mantle.
Geology and geochemistry of a metamorphosed picrite-ankaramite dyke suite from the Seiland province, northern Norway