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TitreLithospheric structure and composition of the Archean western Superior Province from seismic refraction/wide-angle reflection and gravity modeling
AuteurMusacchio, G; White, D J; Asudeh, I; Thomson, C J
SourceJournal of Geophysical Research vol. 109, no. B3, 2004 p. 1-28, (Accès ouvert)
LiensAbstract - Résumé
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 2002240
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC42D; 42E; 42L; 42M; 43D; 52; 53A; 53B; 53C; 53D/01; 53D/02; 53D/07; 53D/08; 53D/09; 53D/10; 53D/15; 53D/16
Lat/Long OENS -95.0000 -86.0000 53.0000 48.0000
Sujetslithosphère; croûte continentale; structure de la croûte; études de la croûte; manteau terrestre; Archéen; interprétations tectoniques; interpretations sismiques; levés de refraction sismiques; levés de reflexion sismiques; gravité; tectonique; Précambrien
Illustrationslocation maps; geological sketch maps; seismic sections; schematic diagrams; tables; models; graphs; cross-sections; ternary diagrams
ProgrammeLithoprobe Western Superior
Résumé(disponible en anglais seulement)
In 1996, LITHOPROBE acquired two ~600 km long seismic refraction/wide-angle reflection profiles oriented parallel and orthogonal to the regional geologic strike of the Archean western Superior Province of the Canadian Shield. We present results from ray-based travel time inversion of these data, combined with modeling of the long-wavelength gravity field and independent estimates of Vp/Vs (y), all of which constrain the structure and composition of the lithosphere to depths of 120 km. Large variations in lower crustal Vp (6.7-7.5 km s-1), lower crustal y (1.72-1.86), upper mantle Vp (8.0-8.8 km s-1), and Moho depth (32-45 km) are determined. Velocities along orthogonal profiles indicate 8% azimuthal Vp anisotropy (fast propagation normal to strike) in part of the lower crust and >6% azimuthal Vp anisotropy (fast propagation parallel to strike) in a 15-20 km thick layer (layer H) in the upper mantle which dips northward at ~10° from a minimum depth of 48-50 km. Wide-angle reflections identify a deep boundary at ~110-120 km depth along both lines. Lower crustal chemical compositions estimated from Vp, y, and density are generally intermediate (57-66% SiO2) requiring the presence of 25-60% granitic rocks, which is significantly higher than previous estimates (30% intermediate or felsic granulite) for average Archean crust. The anisotropic lower crustal layer characterized by anomalously high Vp, high ylc, and low (-7%) relative density values is interpreted as an amphibolite (basic-intermediate composition) having a subhorizontal lineation to account for 8% azimuthal Vp anisotropy. The high Vp and intermediate anisotropy of upper mantle layer H requires a harzburgite peridotitic composition with the a axis of olivine aligned E-W. We suggest that both of these layers are relic oceanic lithosphere accreted at the base of the crust during the final stages of lithospheric assembly in the western Superior Province at ~2.7 Ga.