Early Paleoproterozoic felsic and mafic magmatism in the Karelian province of the Fennoscandian shield

Abstract

Early Paleoproterozoic (2.50Ga to 2.39Ga) mafic and felsic intrusions are widespread in the Fennoscandian shield. The bimodal magmatic event reflects an extensional phase in the Archean craton that had been tectonically quiescent for ca. 200Ma after the amalgamation of the continent. The early Paleoproterozoic felsic intrusions are mostly granitic in composition, only one syenitic pluton is known. Geochemically the felsic intrusions are A-type. The mafic layered intrusions were emplaced in the upper crust between the Archean basement and overlying early Paleoproterozoic volcanic rocks. At least two different parental magma compositions were present in the mafic magmatic event. Partial melting of the Archean lower crust due to heating effect of the hot, mafic magmas most probably generated the felsic magmas, which reflect the Nd isotope composition of the source rocks. The irregular distribution of coeval mafic and felsic intrusions within the Karelian province is still an open question.