Devonian ages from 40 Ar/39Ar dating of plagioclase in dolerite dykes, eastern Varanger Peninsula, North Norway.

Abstract

Gas-release spectra derived from the analysis of plagioclase from three geographically distinct but geochemically comparable dolerite dykes from the eastern part of Varanger Peninsula, northern Norway, show similar features and favour and interpretation that the dykes were intruded in Late Devonian time at around 370 Ma. These particular dykes had previously yielded fairly similar, K-Ar whole-rock ages. As one of the dykes had earlier been traced into the Trollfjorden-Komagelva Fault Zone with the aid of proton-magnetometer, this would indicate that all significant, displacive movement along this major fault had ceased by latest Devonian to Early Carboniferous rifting and sporadic mafic magmatism reported from adjacent parts of Kola Peninsula and neighbouring areas along the northeastern margin of the Fennoscandian Shield.