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TitreSever Spur - Chukchi Plateau: conjugate margins?
AuteurOakey, G N; Saltus, R W
SourceSeventh International Conference on Arctic Margins Trondheim, Norway - Abstracts ; .
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160145
ÉditeurGeological Survey of Norway
RéunionSeventh International Conference on Arctic Margins; Trondheim; NO; juin 2-5, 2015
ProgrammePreparation of a submission for an extended continental shelf in the Atlantic and Arctic Oceans under UNCLOS, Délimitation du plateau continental du Canada en vertu de la Convention des Nations Unies sur le droit de la mer (UNCLOS)
Résumé(disponible en anglais seulement)
Two distinctive magnetic lineations are observed in Canada Basin, equidistant from the central linear gravity low interpreted to be an extinct spreading axis. Crustal velocities defined by sonobuoy refraction data indicate that oceanic crust in present only in the central portion of Canada Basin and that most of the basin is underlain by thinned continental and transitional crust. The conjugate pair of magnetic lineations correspond with the landward limit of oceanic crust. Although magnetic anomalies are observed within this oceanic domain, there is no evidence of systematic lineation patterns consistent with sea-floor spreading magnetic reversals. The oceanic crust may have formed during the late Cretaceous 'quiet zone'. (i.e. M0 to C34 / 124 to 84 Ma). The calculated pole-of-rotation for the conjugate pair of magnetic lineations (64.6º N / 130.8º W, 13.2º rotation) is consistent with models for counter-clockwise rotation of the Alaska-Chukotka plate; however, the new pole is significantly further south than previously published poles which implies less curvature in the resulting flow-lines. The new rotation pole has been used to produce a partial paleo-reconstruction of the Amerasia Basin that positions Chukchi Plateau close to Sever Spur. Spreading based on the new pole predicts some transform process between the oceanic domain and the undisturbed Lomonosov Ridge. Whether this was accommodated by a discrete transform structure or a broad zone of deformation is unresolved.
2-D gravity and magnetic models have been developed for Sever Spur and Chukchi Plateau to compare the morphological and physical properties of these conjugate margin features. Seismic reflection profiles collected during collaborative Canadian U.S. icebreaker operations were depth-converted using sonobuoy velocity models and used as constraints for the models. Density values were assigned to different units based on a standard velocity-density relationship. The continental cratons for both models were assigned an upper crust density of 2800 kg/m3 and a lower crustal density of 2900 kg.m3 based on velocity results from a published GSC refraction line.
Moho depths for the 'Sever' model are highly variable (32 to 38 km) suggesting that large blocks of the continental crust were pulled away from the cratonic core but did not fully separate as the margin thinned. Although the structural highs appear to be basement blocks separated by fault-bounded grabens, they could not be modeled as crustal density rocks since the shallow source depths produced very large high frequency anomalies. Low density (2500 kg/m3) and non-magnetic source bodies were required, and suggest that the structural highs are cored by Paleozoic sedimentary units. At the outer edge of the spur and into deep water, an anomalously high magnetized mid-crustal unit (0.1 SI) was required to fit the high amplitude (>650 nT) magnetic anomaly. This unit is not likely to be a volcanic block since a corresponding gravity high would be expected. The adjacent deep-water crust in Canada Basin is thinned to ~12 km. with a Moho depth of ~18 km. There is no evidence for a 2900 kg/m3 lower crustal layer.
Moho depths for the 'Chukchi' model ranged from 28 to 32 km. In contrast with Sever Spur, the edge of the craton (at Northwind Ridge) is near-vertical with little or no evidence of extension. If Sever Spur and Chukchi Plateau are conjugate margins the style of rifting is highly asymmetric. The structural highs were again modelled with low density and non-magnetic source bodies. Finally, the crust adjacent to the craton is thinned (~ 8 km) with an underplated high-velocity layer (assigned a density of 3100 kg/m3) and Moho at ~18 km. A similar magnetic high (> 400 nT) is observed near the cratonic edge which also requires a highly magnetized mid-crustal block in the modeling.
Models for the complex tectonic development of the Amerasia Basin are subjects of heated debate and our new paleo-reconstruction describes only the last episode for the formation of Canada Basin. However, new data are providing improved constraints on crustal structures and new ideas on the regional geological and structural framework are evolving. We show some compelling reasons to suggest that Sever Spur and Chukchi Plateau have similar crustal structures and are likely conjugate margins, but how do we test this? Obviously we need more data.
Résumé(Résumé en langage clair et simple, non publié)
Une nouvelle plaque modèle de rotation tectonique pour l'ouverture du bassin du Canada a été utilisé pour produire un paléo-reconstruction partielle du bassin Amerasia qui positionne l'Alaska Plateau Chukchi près de Sever Spur sur la marge de l'Arctique canadien. Gravité et modèles magnétiques traversant le Spur Sever et du Plateau Tchouktches ont été développés à l'aide de nouvelles données sismiques recueillies au cours des opérations de collaboration Canada-U.S. Brise-glace pour comparer les propriétés morphologiques et physiques de ces caractéristiques de marge conjuguée.