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In 2008, a Vibroseis seismic reflection survey was acquired by Geoscience BC across the eastern part of the volcanic- covered Nechako basin in central British Columbia, where Cretaceous sedimentary rocks have been exhumed along a NNW trend. Good signal penetration through the volcanic cover is indicated by lower crustal reflections at 8-12 s, which were recorded by the entire seismic survey. Comparison of the 2008 seismic survey with data from a previous survey indicates that the lack of reflectivity in the earlier surveys is generally representative of the subsurface geology. The seismic data show that ~1700 and ~2900 m thick sub-basins are present at the northern and southern ends of this trend, but the intervening Cretaceous rocks are discontinuous and relatively thin. The creation of a passive-roof duplex by Campanian or later low-angle thrusting is inferred within the thickest Cretaceous strata, but elsewhere faulting is likely related to Eocene extension or transtension. Seismic reflections are also recorded from folded volcanic stratigraphy, the base of the surface volcanic rocks, an underlying volcaniclastic stratigraphy, and intrusions projecting into a Quaternary volcanic cone. Seismic interpretation is complemented by coincident audiofrequency magnetotelluric surveys, from which faulting is inferred at offsets in a regional conductor. No regionally extensive stratigraphy can be identified within the seismic data, and the central Nechako basin appears to be a complex network of small, deformed sub-basins, rather than a single large basin. En 2008, Geoscience BC a acquis un releve sismique reflexion Vibroseis portant sur la partie est du bassin Nechako, recouvert de roches volcaniques; ce bassin est situe dans le centre de la Colombie-Britannique, ou des roches sedimentaires datant du Cretace ont ete exhumees le long d'une tendance NNO. Une bonne penetration du signal a travers le couvert volcanique est indiquee par les reflexions sur la croute inferieure a 8-12 s, lesquelles sont enregistrees dans tout le releve sismique. Une comparaison entre le releve sismique de 2008 et les donnees d'un releve anterieur indique que le manque de reflectivite dans les anciens releves est generalement representatif de la geologie souterraine. Les donnees sismiques montrent que des sous-bassins d'une epaisseur ~1700 et ~2900 m sont presents aux extremites nord et sud de cette tendance, mais que les roches cretacees entre les extremites sont discontinues et relativement minces. La creation, vers le Campanien ou plus tard, d' un << duplex >> a toit passif par chevauchement a angle faible est inferee dans les strates cretacees les plus epaisses, mais ailleurs, les failles sont plus probablement reliees a l'extension a l'Eocene ou a de la transtension. Des reflexions sismiques sont aussi enregistrees a partir de la stratigraphie de roches volcaniques pliees, de la base des roches volcaniques en surface, d'une stratigraphie volcano-clastique sous-jacente et a partir d'intrusions se projetant dans un cone volcanique quaternaire. L'interpretation sismique est completee par des releves magnetotelluriques de frequences audio coincidents, a partir desquels les failles sont inferees aux points de decalage dans un conducteur regional. Aucune stratigraphie regionale extensive ne peut etre identifiee dans les donnees sismiques et le bassin Nechako central semble etre un reseau complexe de petits bassins deformes plutot qu'un seul grand bassin. [Traduit par la Redaction], Introduction The Nechako basin, which is located in the interior plateau of British Columbia between the Coast Mountains and the Rocky Mountains (Fig. 1), has seen very little exploration for [...]

Electromagnetic studies of the Precambrian basement beneath the Western Canada Sedimentary Basin in Alberta indicate a narrow linear conductivity anomaly spatially correlated with a strong positive magnetic feature, the Red Deer high. The conductor is located below sedimentary cover near the top of the crystalline basement and has limited depth extent. We propose that this anomalous feature represents graphitic metasedimentary rocks in the euxinic-flysch facies of a Proterozoic foredeep sequence. The strong magnetic anomaly results from an associated iron formation deposited on the outer ramp of the foredeep. This model explains the geophysical anomalies, has analogues on the exposed shield, and is consistent with the timing, deformation history, and known geology of the Precambrian basement.

Presents research which studied the electrical conductivity of the subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada. Conductivity compared with that of the nearby Paleoproterozoic crust; Conductivity based on olivine; Results of mantle xenolith and geological mapping; Effects of tectonically-induced metasomatism.