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TitlePetrogenesis of the Dunite Peak ophiolite, south-central Yukon, and the distinction between upper-plate and lower-plate settings: a new hypothesis for the late Paleozoic-early Mesozoic tectonic evolution of the Northern Cordillera
AuthorParsons, A JORCID logo; Zagorevski, AORCID logo; Ryan, J J; McClelland, W C; van Staal, C RORCID logo; Coleman, M JORCID logo; Golding, M L
SourceGeological Society of America Bulletin 2018 p. 1-25, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170313
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
NTS105E/09; 105F/12
Lat/Long WENS-134.1600 -133.8600 61.6700 61.5500
Subjectsgeochronology; geochemistry; igneous and metamorphic petrology; tectonics; stratigraphy; ophiolites; crustal studies; crustal evolution; tectonic setting; tectonic evolution; tectonostratigraphic zones; subduction zones; accretion; orogenies; obduction; magmatism; island arcs; mid-ocean ridges; oceanic crust; continental crust; intrusions; dykes; sills; metamorphism; bedrock geology; lithology; igneous rocks; intrusive rocks; gabbros; pyroxenites; dunites; harzburgites; lherzolites; leucogabbros; granites; volcanic rocks; tholeiites; basalts; metamorphic rocks; serpentinites; greenstones; metasedimentary rocks; marbles; semipelites; quartzites; sedimentary rocks; shales; cherts; limestones; clastics; structural features; faults; faults, normal; faults, thrust; faults, strike-slip; klippen; radiometric dating; uranium lead dating; zircon dates; neodymium samarium dates; potassium argon dating; argon argon dating; whole rock analyses; whole rock geochemistry; models; petrogenesis; correlations; Canadian Cordillera; Intermontane Belt; Dunite Peak Ophiolite; Yukon-Tanana Terrane; Laurentia; Laurentian Margin; Slide Mountain Ocean; Slide Mountain Terrane; Buffalo Pitts peridotite; Klondike Orogeny; Phanerozoic; Mesozoic; Cretaceous; Triassic; Paleozoic; Permian
Illustrationsgeoscientific sketch maps; photographs; photomicrographs; plots; geochemical plots; tables; ternary diagrams; models; geochronological charts
ProgramGEM2: Geo-mapping for Energy and Minerals Western Cordillera, Devonian and Permian structural architecture
Released2018 08 16
AbstractUpper-plate and lower-plate settings within subduction zones have distinct geological signatures. Identifying and discriminating between these settings is crucial to the study of accretionary orogens. We applied this distinction to the Northern Cordillera in Yukon, British Columbia, and Alaska, and we focused on the identification of upper-plate and lower-plate domains during the late Paleozoic to early Mesozoic evolution of the allochthonous Yukon-Tanana terrane, the west Laurentian margin, and the intervening Slide Mountain Ocean. We present new data from the Dunite Peak ophiolite in south-central Yukon, previously interpreted as ocean plate stratigraphy that was obducted from the subducting Slide Mountain Ocean (i.e., lower plate). Whole-rock geochemical and Sm-Nd isotopic analyses, and U-Pb zircon geochronology indicate that the Dunite Peak ophiolite formed in an intra-oceanic suprasubduction-zone setting (i.e., upper plate) with magmatism at 265 ± 4 Ma. We propose that the Dunite Peak ophiolite correlates with other mid-Permian suprasubduction-zone ophiolites of the Slide Mountain terrane, collectively defining the previously unrecognized mid-Permian “Dunite Peak intra-oceanic arc.” This intra-oceanic arc was active from ca. 280 to 260 Ma, located within the Slide Mountain Ocean, between the Yukon-Tanana terrane and west Laurentia. Existence of this arc is incompatible with previous models proposing that accretion of the Yukon-Tanana terrane to Laurentia was facilitated by Permian subduction of the Slide Mountain Ocean beneath the Yukon-Tanana terrane. Our results, combined with existing data sets, suggest that during the mid- to Late Permian (Late Permian = Guadalupian to Lopingian, 272 Ma to 252 Ma), the Yukon-Tanana terrane was subducted eastward beneath the Dunite Peak intra-oceanic arc. Subsequent collision and accretion of the Yukon-Tanana-Dunite Peak composite terrane with Laurentia must have occurred after the Middle Triassic.
Summary(Plain Language Summary, not published)
The Dunite Peak ophiolite (DPO) is a block of segmented ocean lithosphere in the Northern Cordillera of south-central Yukon that has been tectonically emplaced on continental crust of the Yukon-Tanana terrane (YTT). Geochronology indicates that the DPO formed from volcanism at 265 ± 4 Ma and correlate with similar aged ophiolites elsewhere in western Canada and eastern Alaska. Geochemical analyses indicate that these ophiolites formed from magmatism along a chain of volcanoes situated above a subduction zone in a setting similar to the SE Pacific archipelagos. We name this volcanic chain the Dunite Peak intra-oceanic arc. We propose a new model for the tectonic evolution of the Northern Cordillera in which deformation and mountain building occurred in response to tectonic collision between YTT and the Duntie Peak intra-oceanic arc during the mid to late Permian.

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