Palaeomagnetic data bearing on the age of the Ytterøy dyke, central Norway

Abstract

Abstract The Ytteroy dyke has a near-isotropic fabric and clearly post-dates Caledonian regional deformation. It has a two-component magnetization structure with a low-blocking temperature component ( D = 016°, I = +73°, α 95 = 9) removed below 300° C. The high-blocking temperature component ( D = 216°, I = −42°, α 95 = 8) could be primary in origin. The palaeomagnetically obtained age accords well with an RbSr biotite age of 256 ± 10 Ma, and it could be argued that intrusion of the Ytteroy dyke was related to extensive Permian rifting and faulting within the More Trondelag Fault Zone. Tentatively we ascribe the previously claimed late Devonian age (KAr and 40 Ar 39 Ar biotite ages) for the Ytteroy dyke as resulting from the presence of excess Ar or alternatively, K loss induced by a later hydrothermal flux.