The natural remanent magnetizations of the exeter volcanic traps (Permian, Europe)

Abstract

The natural remanent magnetizations of 35 samples from five quarries in the Permian traps from the Exeter region were carefully examined. A considerable number of the samples contained a secondary magnetism, the intensity of which was directly proportional to the susceptibility. This secondary magnetism (probably of viscous origin) was completely eliminated with a.c. magnetic fields up to 400 Oe. Only the samples from one quarry (Killerton) had in addition much harder secondary magnetism. Besides, all traps contained a harder remanent magnetization whose direction was similar in all samples and thus characteristic for these Exeter traps. This characteristic magnetization mostly was composed of a soft and a hard component. Both components differ very slightly in direction. The intensity of the soft characteristic magnetization did not vary much from sample to sample, but that of the hard characteristic magnetization varied inversely as that of the secondary (viscous) magnetization. When the unfolding test was applied to the mean characteristic magnetization directions of the localities the circle of confidence decreased from 17° to 6°, so this remanent magnetization was acquired before folding took place. It is supposed that this characteristic, pre-tilting remanent magnetization is the fossil primary remanence. It indicates a mean local geomagnetic field direction of D = 198°, I = −25°, corresponding to a virtual pole at 49.5°N 148.5°E. It is argued that during the Permian the virtual geomagnetic pole for Meso-Europe wandered in western direction towards its Triassic position on the east coast of Asia.