The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretical models of grains elongated along [111] and [110] axes are used to show that magnetite needles can exist in stable single-domain configuration in the size and shape ranges of the needles observed in the Michikamau anorthosite. There is thus considerable experimental and theoretical evidence for the conclusion that the stable remanent magnetization of the Michikamau anorthosite is carried by fine single–domain needles of magnetite in the plagioclase felspar.

A paleomagnetic study was attempted of the diabase dike swarm intruding the Grenville structural province of the Canadian Shield. Both the alternating field and thermal demagnetization studies indicated that the dikes have varying degrees of stability of magnetization. Some dikes were shown to have stable primary component of magnetization. Microscopic observations indicated that, in most cases, the primary magnetic mineral titanomagnetite was altered to titanomaghemite, probably due to low temperature oxidation. A good correlation is obtained between magnetic stability and relative abundance of titanomagnetite to titanomaghemite in that dike. The mean paleomagnetic pole for the Grenville dike swarm, which is probably of late Precambrian age, was computed to lie at 3.0° N, 29.0° W with A25 = 11.0°. Comparison of this result with other Precambrian pole positions of similar age relative to North America suggests that the dikes were intruded after the Grenville orogeny.

The Foyers Sandstone, a constituent of the Old Red Sandstone of northern Scotland, located on the eastern flank of the Great Glen Fault, has yielded a multicomponent palaeomagnetic structure. The principal magnetization (called the B component), with in situ mean direction D, I = 185", +8"; ag5 = 2.7", post-dates the local 'mid'-Devonian (Acadian) tectonic event, but this direction corresponds well with characteristic directions displayed by Devonian and Lower Carboniferous rocks of Scotland. The most significant overprinted component, the A2 magnetization, with in situ mean direction D , I = 194", -27"; ag5 = 4. lo, has a more patchy occurrence than the B remanence, the strongest development of A2 being observed at sites that are situated close to the Great Glen Fault zone. The A2 direction is consistent with a Hercynian age. A third magnetization, the A1 component, of suggested Lower Tertiary age, has been found at one of the sites close to the fault zone. The A2 and B remanences support previously proposed declination discordances in corresponding magnetizations across the Great Glen Fault. It is concluded that the Foyers Sandstone developed its multicomponent magnetization through repeated tectonic events on the Great Glen Fault in Acadian, Hercynian and Alpine times respectively.

A paleomagnetic study was carried out on two post-Grenvillian units in the Grenville Province of southeast Labrador. These are (i) a swarm of northeast-trending mafic dykes inferred to be part of the Long Range suite and (ii) the Double Mer Formation, which is an undated rift-related red-bed sequence. Three of six mafic dykes investigated, including two having K–Ar (minimum) ages of 514 ± 8 and 553 ± 22 Ma, carry an interpreted primary remanence of declination (D) = 124.8°, inclination (I) = 55.5° (k = 48, α95 = 18.0°), with the corresponding paleopole at 10.8°S, 164.3°E. Three dykes, including one previously dated at 615 ± 2 Ma (U–Pb), yielded anomalous results. Nevertheless, because all six dykes show similar field, petrographic, and chemical characteristics, we consider that they belong to a single swarm. The anomalous directions are interpreted as disturbed paleomagnetic signatures, and the 615 Ma age is extrapolated as dating the primary remanence in the undisturbed dykes. The Double Mer Formation yields a mean direction for five sites at D = 110.8°, I = 50.1° (k = 24.6, α95 = 15.7°), with a corresponding paleopole at 13.0°S, 178.6°E. The similarity of this direction with that for mafic dykes is the first quantitative indication of its previously suspected Eocambrian age. Combining the Long Range dyke and Double Mer data, the paleolatitude of Eocambrian southeast Labrador is estimated to be 26 ± 5°S.

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