In order to test plate tectonic hypotheses for the Hercynian orogeny in western Europe, Late Devonian and Cambro-Ordovician redbeds and volcanics have been palaeomagnetically studied. The Late Devonian redbeds show nearly univectorial remanent magnetizations during stepwise thermal, chemical and alternating field demagnetization and yield a pole position at 19.8' N, 144.2' E. All three Cambro-Ordovician units studied yielded characteristic directions of magnetization that are interpreted as remagnetizations of Late Devonian-Early Carboniferous age on the basis of negative fold tests, similarities with the directions of the Late Devonian redbeds, reset K/Ar ages of 345 MA, or the occurrence of significant hightemperature magnetizations. A comparison of a mean Late Devonihn-Early Carboniferous pole for all four formations (28.1' N, 146.4" E, d p = 3.87", drn = 7.50") from the Armorican Massif with contemporaneous poles from stable ('extra-Hercynian') Europe indicates that there was little or no separation between Hercynian and stable Europe in that time. A significant separation between the Armorican Massif and Gondwanaland, on the other hand, suggests that an intervening middle Palaeozoic ocean existed which subsequently was consumed by subduction somewhere to the south of the Armorican Massif. Those high-temperature directions from the Cambro-Ordovician redbeds and volcanics that are relatively well grouped are interpreted as original Cambro-Ordovician magnetizations. They show shallow inclinations and north-westerly declinations, but are not sufficiently substantiated to give more than the tentative interpretation that their palaeolatitudes also are roughly in agreement with the data from stable Europe for that time.
Paleozoic limestone, graywacke, sandstone, milestone, red beds and volcanic rocks of the Alexander terrane, southeastern Alaska, have yielded six paleomagnetic pole positions after thermal and alternating‐field demagnetization. These poles are from sample groups of late Middle Ordovician, Late Ordovician, Devonian, Late Devonian, and early and late Carboniferous age. To test various tectonic models for the structural development of this part of western North America, the paleomagnetic results are compared to those for the North American craton. It is found that the observed inclination and declination values deviate significantly from the values predicted for the present‐day position of the Alexander terrane (55.5N, 133.5W). Better matching can be obtained for a paleoposition of the terrane at about 40N, 120W, in the present position of western Nevada and northeastern California. In addition, an in situ 25° clockwise rotation of the terrane is required to restore it to its original position.
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