Precambrian volcanic rocks exposed in structural highs of the Avalon zone of Newfoundland are marked by high magnetic anomalies whose continuity offshore permits recognition of the extent of the Avalon zone, particularly on the Grand Banks. South of Newfoundland and in the Gulf of St. Lawrence, where the magnetic pattern is less well defined, the Avalon platform can also be recognized by the existence of seismic velocities of the order of 6.6 km s−1, which are apparently associated with volcanic rocks. The magnetic Collector Anomaly running eastwards from Cape Breton across the southern Grand Banks is the southern limit of these Avalonian markers, while the northern boundary follows a serrated path (the offsets apparently caused by a series of northwest-trending faults) from the Belle Isle Fault in New Brunswick to the Hermitage and Dover Faults in Newfoundland, thence to the western end of the Charlie Fracture zone. These Avalonian boundaries provide markers for the constraint of pre-drift continental reconstructions.
Geological interpretation of geophysical data (magnetic, gravimetric and seismic) on the western European and eastern Canadian shelves indicates a transatlantic correlation between the major late Paleozoic fractures of those areas.East-west megafractures, which are primarily grouped in two latitudinal belts at 44" N and 48" N, are the most obvious and correlative. The first zone offractures was an extension of the South Arrnorican shear zone, which continued to the north of Flemish Cap. The second was an eastwards extension of the Cobequid-Chedabucto-Scatarie Fault, which crossed Galicia Bank, northern Spain and southern France. A third zone possibly existed between the Clinton-Newbury Fault of New England and mid-Spain, Corsica and Sardinia (when they are moved back to their late Paleozoic positions). The location of the shortening trajectories shows that the first two zones (and perhaps the third one) belonged to the same stress system during late Carboniferous. As a hypothesis, different rates of displacement between 'peri-Atlantic' plates during their northward movement in Late Carboniferous time could be the source of the stress.L'interpretation geologique des donnees geophysiques (magnetisme, gravimetrie, sismique) sur les plateaux continentaux ouest europeen et est canadien permet de correler les principales fractures depart et d'autre de I1Atlantique Nord.Les megafractures est-ouest sont les plus evidentes et les plus aisees a mettre en correlation; elles sont associees selon deux ceintures est-ouest a la latitude de 44" N et 48" N. La premiere s'etend a I'ouest de la zone broyee sud armoricaine et elle traverse au nord de Flemish Cap. La seconde prolonge vers I'est de la faille Cobequid-Chedabucto-Scatarie; elle traverse les bancs de Galice, le nord de I'Espagne et le sudde laFrance. Une troisieme ceinture existe peut-Ctre entre la faille Clinton-Newbury (Massachusetts, E.U.), le milieu de I'Espagne, la Corse et la Sardaigne (quand celles-ci sont replacees a I'endroit qu'elles occupaient au Paleozoique terminal).La repartition des trajectoires de raccourcissement montre que les deux ceintures (et peut-Ctre la troisieme) appartenaient au mtme systtme de contraintes. On emet I'hypothese que ces contraintes pourraient ttre dues a une difference de vitesse entre les plaques 'periatlantiques' durant leur deplacement vers le nord au cours du Carboniferes terminal.
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