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TitleA lost arc-back-arc terrane of the Dunnage oceanic tract recorded in clasts from the Garin Formation and McCrea Mélange in the Gaspé Appalachians of Québec
AuthorDupuis, C; Malo, M; Bédard, J H; Davis, B; Villeneuve, M
SourceGeological Society of America Bulletin vol. 121, no. 1/2, 2009 p. 17-38,
Alt SeriesEarth Sciences Sector, Contribution Series 20070521
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
ProvinceQuebec; New Brunswick
NTS21O/09; 21O/10; 21O/15; 21O/16; 21P/10; 21P/11; 21P/12; 21P/13; 21P/14; 21P/15; 22A; 22B/01; 22B/02; 22B/07; 22B/08; 22B/09; 22B/10; 22B/15; 22B/16
AreaGaspé; Appalachians
Lat/Long WENS-67.0000 -64.0000 49.1667 47.5000
Subjectsstratigraphy; structural geology; tectonics; geochemistry; geochronology; bedrock geology; sedimentary rocks; conglomerates; igneous rocks; magmatic arcs; volcanic rocks; magmas; tholeiites; lavas; magmatism; plate tectonics; tectonic history; tectonic stages; tectonic interpretations; tectonostratigraphic zones; biostratigraphy; petrography; whole rock geochemistry; whole rock analyses; geochemical analyses; Garin Formation; McCrea Mélange; Gaspé Belt; Humber Zone; Dunnage Zone; Paleozoic; Ordovician
Illustrationslocation maps; ternary diagrams; stratigraphic charts; plots; cross-sections; Concordia diagrams
AbstractUpper Ordovician Garin conglomerates (base of the Gaspé belt, Québec Appalachians) contain three igneous clast populations. (1) Calc-alkaline intermediate-felsic rocks resemble Exploits (New Brunswick, Maine) and Notre Dame (Québec, Newfoundland) subzone lavas. Clasts (monzoniterhyodacite) give U-Pb zircon ages between 465 and 466 Ma, precluding correlation with Exploits rocks. We suggest that the suite represents peri-Laurentian continental arc magmas coeval with the Red Indian Lake Group of Newfoundland. Correlation of lavas from a Gaspé well with the Popelogan arc implies that the Red Indian Line passes through southern Gaspé. (2) Mafi c tholeiiticto-
alkaline clasts resemble New Brunswick and Maine (Exploits subzone) alkaline lavas. We interpret them as magmas associated with initiation of a back-arc basin, possibly on the Laurentian margin. (3) Mafi c-intermediate tholeiitic to calc-alkaline clasts have an oceanic subduction component and correlate with Notre Dame subzone lavas Québec, Newfoundland). They are interpreted as products of spreading and off-axis magmatism of a peri-Laurentian back-arc basin. We correlate McCrea mélange lavas to the calcalkaline intermediate-felsic and mafi c-intermediate suites and interpret them as samples of a Notre Dame subzone terrane coeval with the Red Indian Lake Group of Newfoundland during initiation of a successor arc-backarc, a terrane which is no longer preserved in New Brunswick and Maine but that provides some evidence for possible extensions of Newfoundland's geology into the Gaspé Appalachians of Québec. A mid-ocean-ridge basalt-like intrusion in the McCrea mélange (Ar-Ar age: 471.2 ± 11.2 Ma) is coeval with peri-Laurentian ophiolites in Newfoundland and may record a back-arc opening event.