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TitleThermochronology of the Yukon-Tanana Terrane, West-Central Yukon: Evidence for Jurassic Extension and Exhumation in the Northern Canadian Cordillera
AuthorKnight, E; Schneider, D A; Ryan, J
SourceJournal of Geology vol. 121, 2013 p. 371-400,
Alt SeriesEarth Sciences Sector, Contribution Series 20120375
PublisherUniversity of Chicago Press
Mediapaper; on-line; digital
File formatpdf
NTS105M/13; 105M/14; 106D/03; 106D/04; 106D/05; 106D/06; 116A/01; 116A/02; 116A/07; 116A/08; 115P/15; 115P/16
AreaNorthern Cordillera; Stewart River; Glenlyon; Finlayson; Yukon-Tanana Upland
Lat/Long WENS-136.0000 -131.0000 63.0000 61.0000
Subjectsgeochronology; igneous and metamorphic petrology; structural domains; metamorphic rocks; deformation; plutonic rocks; argon argon dates; argon argon dating; uranium thorium ratios; uranium thorium dates; radiometric dates; radiometric dating; Yukon-Tanana Terrane; Willow Lake fault; Paleozoic; Devonian; Mississippian; Pennsylvanian
Illustrationslocation maps; photographs; plots; tables; photomicrographs
ProgramGEM: Geo-mapping for Energy and Minerals Multiple Metals - NW Canadian Cordillera (Yukon, B.C.)
Released2013 07 01
AbstractIn the McQuesten area of the central Yukon, the Willow Lake fault juxtaposes two crustal domains: i) on the northeast side, the Reid Lakes complex, an unmetamorphosed and predominantly undeformed Devono-Mississippian assemblage of plutonic and volcanic rocks, and ii) on the southwest side, typical Yukon-Tanana terrane (YTT), deformed greenschist to amphibolite facies metamorphosed pre-Late Devonian to Late Permian rocks of the Canadian Cordillera. SHRIMP U-Pb ages delineate Middle to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the YTT. Notably, ca. 193 Ma zircon overgrowths and patches of recrystallized zircon with low Th/U ratios are recorded in samples proximal to the fault. Mississippian (ca. 349 to 325 Ma) 40Ar/39Ar cooling ages from biotite and hornblende of the Reid Lakes complex suggest cooling immediately following volcanism and batholith emplacement. Plutonic samples near the fault trace and exhibiting weak to high strain yield younger ca. 193 to 191 Ma biotite 40Ar/39Ar ages. Zircon (U-Th)/He ages from the magmatic complex reflect ca. 216 to 214 Ma cooling through the uppermost crust of structurally higher volcanogenic rocks, followed by ca. 159 to 130 Ma cooling of the deeper-seated plutonic phase. Across the Willow Lake fault, YTT metamorphic rocks yielded ca. 197 to 165 Ma biotite and hornblende 40Ar/39Ar ages and ca. 113 to 90 Ma zircon (U-Th)/He ages. The marked step in cooling ages across the fault and the juxtaposition of the deformed rocks against undeformed rocks strongly indicates the Willow Lake fault is extensional (top down to the northeast), and exhumed the middle crust commencing in the Early Jurassic. Magmatism of the Aishihik suite of the Stikinia/Quesnellia arc in the McQuesten area yielded a zircon age of ca. 205 Ma and 40Ar/39Ar cooling ages of the suite at ca. 205-196 Ma. In conjunction with the presence of epidote that appears to be magmatic in origin, the Aishihik suite cooled rapidly and was
exhumed from mid-crustal levels, further illustrating the significance of the Jurassic event that exhumed the central belt of Yukon-Tanana rocks. A similar tectonothermal evolution has been documented in the nearby Stewart River area, along strike from McQuesten, which was attributed to transtensional exhumation and cooling during slab rollback, leading to unroofing of the outboard regions of the terrane. The Yukon Tanana terrane in the region is bounded on its northeast side by the dextral Eocene Tintina fault. We suggest that Early Jurassic extensional exhumation of this domain was mechanically linked to a Jurassic manifestation of the Teslin Fault system and was more widespread that previously considered, likely accommodating crustal thinning from the Yukon-Tanana upland of eastern Alaska to the Glenlyon region of the central Yukon. Parts of this system may have been reactivated and overprinted as part of the Eocene Tintina fault, masking the early history.

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