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TitleGeochemical constraints on the origin of the Annieopsquotch ophiolite belt, Newfoundland Appalachians
AuthorLissenberg, C J; van Staal, C R; Bédard, J H; Zagorevski, A
SourceGeological Society of America Bulletin vol. 117, no. 11-12, 2005 p. 1413-1426,
LinksSupplementary Data - Données supplémentaires
Alt SeriesGeological Survey of Canada, Contribution Series 2004277
PublisherGeological Society of America
Mediapaper; on-line; digital
File formathtml; pdf
ProvinceNewfoundland and Labrador
NTS12A/04; 12A/05; 12A/06; 12A/10; 12A/11
AreaLloyds Lake; Red Indian Lake
Lat/Long WENS -58.1667 -56.7500 48.8333 48.0000
Subjectsgeneral geology; igneous and metamorphic petrology; mineralogy; structural geology; tectonics; ophiolites; sutures; plate tectonics; gabbros; dykes; basalts; troctolites; tholeiites; magmas; subduction zones; magmatic arcs; whole rock geochemistry; orogenies; tectonic evolution; Appalachians; Iapetus; geochemistry; boninite; suprasubduction zone
Illustrationslocation maps; photographs; graphs; structural diagrams; geological sketch maps; geochemical plots
ProgramTargeted Geoscience Initiative (TGI-1), 2000-2003
ProgramNSERC Natural Sciences and Engineering Research Council of Canada
ProgramUniversity of Ottawa, Faculty of Graduate and Postdoctoral Studies
AbstractThe Early Ordovician Annieopsquotch ophiolite belt occurs immediately west of the main Iapetus suture zone, and imposes important constraints on the tectonic processes associated with closure of the peri-Laurentian portion of Iapetus. The Annieopsquotch ophiolite, the most prominent ophiolite within the Annieopsquotch ophiolite belt, exposes a 5.5-km-thick section of gabbros, sheeted dikes, and pillow basalts, in which three magmatic episodes have been recognized based on fi eld and geochemical data. The fi rst phase is composed of layered troctolites, which are preserved as enclaves within the gabbro zone. Trace element modeling suggests the troctolites crystallized from boninitic melts. The troctolite substrate was intruded by the dominant, second, tholeiitic magmatic phase, which formed a gabbro-sheeted dike-basalt sequence. All tholeiites have suprasubduction zone chemical characteristics, but the suprasubduction zone signature decreases toward the top of the basalt sequence. The third magmatic episode is composed of primitive dikes, which are interpreted as off-axis intrusions. Other ophiolites within the Annieopsquotch ophiolite belt have comparable geochemical signatures, suggesting they may have constituted a single piece of oceanic lithosphere. Based on geochemical and regional tectonic constraints, the Annieopsquotch ophiolite belt is interpreted to have formed during initiation of west-directed subduction. Fast rollback of the subducting slab would have induced volatile-fl uxed decompression melting of previously depleted mantle, yielding boninitic melts. The uprasubduction zone tholeiite sequence would have formed from ascending fertile mantle fl uxed with subduction- related fl uids as ollback continued. This suggests that the Annieopsquotch ophiolite belt does not represent the remnants of normal oceanic crust or ackarc basin crust, as previously thought. Our model constrains the initiation and early evolution of a westdipping peri-Laurentian ubduction zone that was responsible for formation of several arc-backarc complexes currently preserved in the Annieopsquotch ccretionary Tract.

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