Geochemistry and petrology of dolerite dykes of probable late Caledonian age from the outer Sunnfjord region, West Norway.

Abstract

Major and trace element abundances from dolerite dykes in the outer Sunnfjord region show an averall compositional similarity to continental tholeiites. The dyke rocks exhibit a fractionated nature, especially with respect to a strong enrichment in total Fe and in Ti. The fractionation apparently took place in a deep-seated magma chamber where plagioclase and clinopyroxene were formed as phenocrysts. During ascent of the magma, suspended pyroxene phenocrysts underwent marginal growth and strong resorption of plagioclase primocrysts took place. The PT variation trend during intertelluric crystallization of the Sunnfjord dolerite magmas has been outlined on the basis of textural features and mineral compositions. The geological relationships in the area indicate that the emplacement of the dyke swarm took place in the Lower Devonian and may thus represent the youngest igneous event in the outer Sunnfjord region.