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TitreEarly Mesozoic magmatism on the eastern Canadian margin: petrogenetic and tectonic significance
AuteurPe-Piper, G; Jansa, L F; Lambert, R St J
SourceEastern North American Mesozoic magmatism; par Puffer, J H (éd.); Ragland, P C (éd.); Geological Society of America, Special Paper vol. 268, 1992 p. 13-36,
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 25791
ÉditeurGeological Society of America
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceRégion extracotière de l'est
Lat/Long OENS -70.0000 -50.0000 48.0000 42.0000
Sujetsfilons rocheux; tholéiites; roches ignées; magmatisme; marges continentales; marges plaques; rapports des isotopes de plomb; datation au potassium-argon; datations au plomb-plomb; études de la croûte; modèles tectoniques; discordances
Illustrationslocation maps; tables; stratigraphic cross-sections; plots; graphs
ProgrammeCRSNG Conseil de recherches en sciences naturelles et en génie du Canada
Diffusé1992 01 01
Résumé(disponible en anglais seulement)
In eastern Canada, two periods of magmatism were associated with early Mesozoic continental rifting. Triassic dikes in southwest Nova Scotia and the Northumberland Strait F-25 well geochemically resemble alkaline dikes of the coastal New England (CNE) igneous province. Widespread Hettangian tholeiitic magmatism of the eastern North America (ENA) province is represented in eastern Canada by extensive multiple basalt flows around the Bay of Fundy and on the Scotian Shelf and Grand Banks and by several dikes hundreds of kilometers long.
The total volume of observed Mesozoic magmatic products on the eastern Canadian margin is small. They were probably emplaced over relatively short time intervals, indicating the importance of tectonic pathways in permitting rise of magma to the surface. Samples from the CNE province and the Glooscap well on the west Scotian Shelf have more highly radiogenic Pb isotope compositions. Samples from southwestern Nova Scotia are enriched in LILE, and have higher Hf/Lu and lower Y/Nb compared with samples from Newfoundland and northern New Brunswick. Such geochemical trends are interpreted to result from the Permian-Triassic hotspot responsible for resetting of K-Ar dates and plutonic activity in New England. The progression from alkalic to tholeiitic magmatism through time is related to this plume. Other early Mesozoic basaltic rocks in eastern Canada have isotopic composition (low eNd and high 207Pb/204Pb) and trace element features (such as high La/Ta and low Ti/V) that reflect incorporation of crustal-type material in subcontinental mantle, perhaps by previous subduction. Geochemical comparison with Carboniferous tholeiites suggests that the early Mesozoic tholeiites have not been generally contaminated by continental crust, except for some local fluid phase interaction. The magmas resulted from adiabatic decompression of asthenosphere as a result of continental extension and subsequent plagioclase and pyroxene fractionation in mid-crustal reservoirs.
Three major tectonic and igneous phases are distinguished: (1) Anisian to early Hettangian rifting, accompanied by minor alkalic dikes (CNE province), when basins formed by extension and were filled by thick terrigenous clastics and evaporites; (2) a postrifting phase (late Hettangian to Bajocian), separated by a postrift unconformity from underlying strata. This Hettangian unconformity is not a breakup unconformity. ENA magmatic activity (tholeiitic plateau basalts and linear composite dikes, up to 400 km landward of the hinge line) was localized along major deeply penetrating faults. The change in tectonic regime resulted in accelerated lithospheric attenuation accompanied by uplift landward of the hinge zone and an increase in subsidence seaward. (3) The final separation of continental crust and onset of oceanic rifting took place in the Bajocian and was accompanied by only limited igneous activity near the ocean-continent boundary.