Late Proterozoic and Palaeozoic (pre-Permian) palaeomagnetic data from all regions involved in, or adjacent to, the Caledonian-Appalachian orogenic belt are reviewed. Between about 1100 and about 800 Ma the Laurentian and Baltic shields were close together, prior to the opening phase of the Caledonian-Appalachian Wilson cycle. The problems of tectonic interpretation of Palaeozoic palaeomagnetic data from within and around the belt derive mostly from differences of typically 10°-20 ° between the pole positions. These can variously be interpreted in terms of (i) relative displacements between different continents or terranes, (ii) differences in ages of remanence and (iii) aberrations due to inadequacy of data or geomagnetic complexity, and it is not always easy to discriminate between these alternatives. If the Pangaea A2 reassembly of continents around the northern and central Atlantic is taken as the end-product of Caledonian-Appalachian orogenesis, the following conclusions can be drawn.

A paleomagnetic study of gabbroic and anorthositic members of the Sept-Îles layered mafic intrusion has isolated a remanence with direction D = 333°, I = −29 °(remanence A) and a corresponding pole of 141 °E, 20°N. The rocks are cut by numerous diabase dykes of unknown age. The remanence carried by the dykes has direction D = 188°, I = −85 °(remanence B), with a corresponding pole of 116°E, 59°S. Another remanence, statistically identical to B (D = 186°, I = −85°), is found at dyke contacts and in the local host rock; its associated pole, 115°E, 61°S, is identical to the one derived from the dykes. This overprint is significantly different from remanence A, and is obviously related to dyke emplacement. The location of the pole derived from remanence A is in excellent agreement with many other Cambrian poles from a variety of locations throughout cratonic North America. The rocks at Sept-Îles have been previously dated radiometrically at 540 Ma. Thus, all evidence indicates that remanence A is an original thermochemical remanent magnetization, acquired during initial cooling of the intrusion in the Cambrian and prior to the emplacement of the dykes.

This is the first palcomagnetic result from the Paleozoic Botwood Central Zone of Newfoundland. Two Lower Paleozoic rock units were sampled: the Botwood Group (rhyolite and red sandstone) at 16 sites and the Mount Peyton Batholith (dioritic and granitic phases) at 12 sites. Two phases are recognized in this intrusion: dioritic (420 Ma) and granitic (380 Ma). Four distinct magnetization directions were observed during the study. In the Lawrenceton Formation (Bot-wood Group, rhyolite) the direction obtained after tilt correction (180°, + 47°) gives a pole at 125°E, 13°N, probably of Lower Silurian age. The overlying Wig Wam Formation of the Botwood Group (red sandstone) was magnetized during a reversal. Detailed demagnetization techniques (thermal, chemical, and alternating field) were used to separate the normal and reversed directions in composite magnetizations; with a mean direction of 194°, + 28°, the pole (100°E, 25°N) obtained after tilt correction is related to a Silurian age. Two magnetizations were found in the Mount Peyton Batholith: the first one (pole at 68°E, 15°S) is associated with the dioritic phase with an age of 420 Ma. The second one (pole at 125°E, 63°S) is associated with the granitic phase at 380 Ma.

Magnetic susceptibility measurements on cores from boreholes in the Eye–Dashwa lakes pluton, an Archean granitic pluton near Atikokan, Ontario, give a quantitative evaluation of the alteration level of these rocks. The histogram of the 5406 magnetic susceptibility measurements taken from 3.3 km of cores shows a multimodal distribution. In order to differentiate these subpopulations and to recognize their geological significance a numerical approach is employed. The magnetic susceptibility, when plotted on a log scale versus cumulative frequency on a probability scale, successfully differentiates the interval associated with each respective subpopulation. In the granite zone cut by the five boreholes, three distinct subpopulations are identified.The variation of magnetic susceptibility in the Eye–Dashwa lakes granitic cores studied is almost entirely associated with the oxidation state of the iron–titanium oxide minerals, since the variation in the total iron oxide content and the variation in grain size do not vary sufficiently to explain the large variation detected in the magnetic susceptibility logs. Hence, the variation in magnetic susceptibility is interpreted to be directly related to the alteration level seen in the rock (highly altered rock leads to lower magnetic susceptibility signal). Furthermore, the rocks characterized by the epidote group, the chlorite group, and the iron hydroxides, clays, and carbonate group each have a distinct magnetic susceptibility signature.By identifying the different levels of magnetic susceptibility values at this specific research area, the associated levels of alteration can be defined. Using this approach, a geologically interpreted geophysical log is produced. A three-dimensional representation of the five magnetic susceptibility bore-core logs is interpreted on the basis of similar magnetic susceptibility signature.The proposed approach has also been successfully applied to surface studies and is potentially useful in mineral exploration, especially in areas where mineralization is associated with fractured and altered rocks.

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