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TitreIntra-oceanic production of continental crust in a Th-depleted ca. 3.0 Ga arc complex, western Superior Province, Canada
AuteurWhalen, J B; Percival, J A; McNicoll, V J; Longstaffe, F J
SourceContributions To Mineralogy and Petrology 146, 1, 2003 p. 78-99,
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 2002171
ÉditeurSpringer Nature
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC52M/13; 62P/01
Lat/Long OENS-96.5000 -95.5000 51.2500 51.0000
Sujetscroûte continentale; roches ignées; tonalites; diorites; gabbros; anorthosites; filons rocheux; gneiss; géochimie des éléments majeurs; géochimie des éléments en trace; pétrogenèse; cadre tectonique; magmatisme; Archéen; Terrane de North Caribou ; Subprovince d'Uchi ; Complexe d'East Shore Plutonic ; Assemblage de Lewis ; Assemblage de Storey ; Zone de cisaillement d'English Lake ; Complexe d'English Lake Igneous ; Pluton de Tonalite ; Province de Western Superior ; minéralogie; pétrologie ignée et métamorphique; géochimie; Précambrien
Illustrationssketch maps; tables; graphs; plots
ProgrammeProjet de la Province du lac Spérieur occidentale du CARTNAT
Résumé(disponible en anglais seulement)
The English Lake magmatic complex in the western Superior Province of Canada represents a fragment of early (3.0 Ga) continental crust exposed in oblique cross section through tonalitic upper levels and subjacent quartz diorite, diorite and gabbro, which are cut by late gabbro, anorthosite and hornblendite dykes. Massive, foliated and gneissic units of tonalitic to gabbroic composition, crystallized over a 10 to 18 m.y. period, bear common geochemical attributes, including negative Th, U and Nb anomalies, and only slight LREE and LILE enrichment on NMORB-normalized trace-element profiles. Epsilon Nd values (+0.1to +1.7) and delta-18 O (+6.7 to +8.0 ) do not co-vary with silica or other crustal contamination indices. High Mg#'s and Ni contents suggest derivation from, or interaction with mantle, and large positive anomalies for Ba, Sr and Pb, as well as high U/Th, suggest metasomatism by hydrous fluids. Trace-element profiles resemble those of primitive intra-oceanic island arc magmas except for the negative Th-U anomaly, which precludes the involvement of either oceanic (sedimentary or basaltic) or continental crust in the petrogenesis of English Lake magmas. In order to account for the unusual geochemical character of the suite, we postulate that water-rich fluids derived from subducted, sea-floor-altered serpentinite provided the flux for melting a depleted mantle wedge. Contemporaneous, proximal high Th/Nb tonalites suggest that the zone of serpentinite subduction occurred within a restricted arc segment possibly due to subduction of either: (a) a seamount chain oriented broadly perpendicular to an arc, or (b) a similarly oriented serpentinite-enclosed oceanic fracture zone or fault.