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TitleDetrital zircon evidence for eclogite formation by basal subduction erosion - An example from the Yukon-Tanana composite arc, Canadian Cordillera
AuthorGilotti, J A; McClelland, W C; Van Staal, C RORCID logo; Petrie, M B
SourceThe crust-mantle and lithosphere-asthenosphere boundaries: insights from xenoliths, orogenic deep sections; by Bianchini, G (ed.); Bodinier, J -L (ed.); Braga, R (ed.); Wilson, M (ed.); Geological Society of America, Special Paper vol. 526, 2017 p. 173-189,
Alt SeriesNatural Resources Canada, Contribution Series 20182354
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf; html
NTS105B; 105C; 105D; 105E; 105F; 105G; 105K; 105L; 105M; 105N; 106D; 106E; 115; 116A; 116B; 116C; 116F; 116G; 116H
AreaSt. Cyr; Ross River; Last Peak; Faro; Klatsa River
Lat/Long WENS-142.0000 -131.0000 66.0000 60.0000
Subjectsgeochronology; tectonics; geochemistry; Science and Technology; Nature and Environment; radiometric dating; zircon dates; eclogites; crustal evolution; oceanic crust; continental crust; tectonic history; plate margins; subduction; erosion; accretion; orogenies; metamorphism; deformation; emplacement; bedrock geology; lithology; metamorphic rocks; schists; metatonalites; metagabbros; metavolcanic rocks; metabasalts; metasedimentary rocks; ultramafic rocks; structural features; faults; klippen; metamorphic facies; host rocks; provenance; Canadian Cordillera; Yukon-Tanana Terrane; Peri-Laurentian Arc System; Laurentia; Snowcap Assemblage; Mesoproterozoic; Paleoproterozoic; Klatsa Metamorphic Complex; Tintina Fault; Teslin Fault; Slide Mountain Terrane; North American Platform; St. Cyr Klippe; Finlayson Assemblage; Big Salmon Complex; Yukon-Tanana Arc; Phanerozoic; Mesozoic; Cretaceous; Paleozoic; Permian; Carboniferous; Devonian; Precambrian; Proterozoic
Illustrationslocation maps; geoscientific sketch maps; photographs; photomicrographs; tables; Concordia diagrams; plots; schematic cross-sections
ProgramGEM2: Geo-mapping for Energy and Minerals Western Cordillera, Redefinition of crustal blocks
Released2017 01 01
AbstractThe Yukon-Tanana terrane lies within the North American Cordilleran accretionary orogen and contains strongly deformed, coherent eclogite-bearing units that are candidates for wholesale subduction erosion of large blocks of crust. The Yukon-Tanana terrane is a composite continental arc built on a peri-Laurentian substrate that experienced subduction on both sides before it was accreted back onto Laurentia in the Mesozoic. Along the present-day eastern margin of the terrane, eclogites are found as layers and lenses in quartzofeldspathic schist derived from both igneous and sedimentary protoliths, all metamorphosed together during the Permian. In the St. Cyr area, coherent slices of eclogite-bearing crust up to 30 km long and 1-2 km thick have been mapped. Phengite with Si = 3.3-3.4 per formula unit from the host schists indicates that they also record eclogite-facies metamorphism. Detrital zircon was recovered from six host-rock samples collected at three high-pressure (HP) localities (St. Cyr, Ross River, and Last Peak), and from two eclogite-free units. Samples from the eclogite-free units and Last Peak have detrital zircon signatures with prominent Mesoproterozoic and Paleoproterozoic peaks typical of the Snow-cap assemblage, the peri-Laurentian substrate of the Yukon-Tanana terrane. Detrital spectra from the St. Cyr and Ross River HP localities contain Precambrian, mostly Mesoproterozoic, zircon with significant Paleozoic peaks that match ages of igneous events in the Yukon-Tanana terrane. The coherent slices of crust containing eclogite, meta-tonalite, and arc-derived metasedimentary rocks are interpreted as pieces of Yukon-Tanana terrane that were eroded from the arc during subduction of oceanic lithosphere and reaccreted to the arc prior to Mesozoic emplacement of the Yukon-Tanana terrane onto North America.
Summary(Plain Language Summary, not published)
Eclogitic rocks are shown to have formed by subduction-related erosion form the upper plate rather than from subducting lower plate rocks. Both the eclogite and enveloping rocks were subjected to the same metamorphic conditions.

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