| Title | Late Paleozoic assembly of the Alexander-Wrangellia-Peninsular composite terrane, Canadian and Alaskan Cordillera |
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| Author | Beranek, L P; van Staal, C R ; McClelland, W C; Joyce, N; Israel,
S |
| Source | Geological Society of America Bulletin vol. 126, no. 11-12, 2014 p. 1531-1550, https://doi.org/10.1130/31066.1 |
| Image |  |
| Year | 2014 |
| Alt Series | Earth Sciences Sector, Contribution Series 20140045 |
| Publisher | Geological Society of America |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Yukon |
| Area | St-Elias Mountains; Alaska; Donjek Glacier suite; Barnard Glacier; United States of America |
| Lat/Long WENS | -142.0000 -138.0000 62.0000 59.0000 |
| Subjects | structural geology; general geology; geochronology; terranes; spectrometric analyses; uranium lead dates; niobium geochemistry; strontium geochemistry; tectonic history; Permian; Paleozoic |
| Illustrations | location maps; diagrams; photographs; plots; element distribution diagrams |
| Program | GEM: Geo-mapping for Energy and Minerals Multiple Metals - NW Canadian Cordillera (Yukon, B.C.) |
| Released | 2014 06 23 |
| Abstract | Late Paleozoic assembly of the Alexander- Wrangellia-Peninsular composite terrane is recorded by two phases of regional deformation, metamorphism, and magmatism within basement complexes of the
Alexander (Craig and Admiralty subterranes), Wrangellia, and Peninsular terranes in the Canadian and Alaskan Cordillera. New secondary ion mass spectrometry (SIMS) and chemical abrasionisotope dilution-thermal ionization mass spectrometry
(CA-ID-TIMS) zircon U-Pb ages, whole-rock major- and trace-element and Nd-Sr isotope geochemical compositions, and geological fi eld observations of late Paleozoic igneous rocks were used to identify the precise timing and signifi cance of this
tectonism in the Saint Elias Mountains region of southwestern Yukon and eastern Alaska. Middle to Late Pennsylvanian (301-307 Ma) igneous rocks, herein assigned to the Barnard Glacier suite, were preferentially emplaced along the Wrangellia-Craig
subterrane boundary and mainly comprise syenitic plutons that intrude Paleozoic country rocks with evidence of Pennsylvanian or older (D1) deformation. We propose that Barnard Glacier suite magmatism was produced by a slab breakoff event after the
consumption of a narrow backarc ocean basin and early Pennsylvanian collision between the Wrangellia- Peninsular arc and Craig subterrane passive margin. Early Permian (284-291 Ma) dioritic to granodioritic rocks, herein assigned to the Donjek
Glacier suite, comprise the vestiges of an extensive magmatic system within the Craig subterrane of southwestern Yukon and southeastern Alaska. The available data suggest that the Donjek Glacier suite represents part of a short-lived, Early Permian
arc that initiated along the outboard margin of the Craig subterrane-Wrangellia-Peninsular block after Pennsylvanian collision and slab breakoff. At two fi eld localities in southwestern Yukon, Paleozoic country rocks with D1 fabrics are also
intruded by sills and dikes of the Donjek Glacier suite that show evidence of ca. 285 Ma regional deformation and metamorphism (D2). Field evidence for Early Permian tectonism in the Saint Elias Mountains implies direct connections with coeval
deformation and metamorphism in the Admiralty subterrane, a microcontinent in the Admiralty Island region of southeastern Alaska that developed separately from the Craig subterrane prior to the Early Per mian. D2 tectonism was likely related to the
entry of the Admiralty subterrane margin into the Early Permian subduction zone, which resulted in collision and fi nal amalgamation of the Alexander-Wrangellia-Peninsular composite terrane. Our tectonic scenarios require the currently accepted confi
guration of the Alexander terrane (com posite of the Craig and Admiralty subterranes) to have only existed after the Early Permian collision between the Admiralty subterrane and the previously assembled Craig subterrane- Wrangellia-Peninsular
terrane. Biogeographic and other geological data suggest that the two-part assembly of the Alexander- Wrangellia-Peninsular composite terrane took place along a convergent margin to the north of the Cordilleran pericratonic arc terranes
(Yukon-Tanana, Quesnellia, and others ), in between the paleo -Pacifi c Ocean and paleo-Arctic Ocean realms, to the northwest of the supercontinent Pangea. The assembly of the Alexander-Wrangellia-Peninsular composite terrane might have been
associated with the Early to Middle Permian subduction polarity fl ip recognized in the Cordilleran pericratonic realm, which led to the closure of a backarc ocean basin and Late Permian arc-continent collision along the western margin of North
America. |
| Summary | (Plain Language Summary, not published)
Geochronology of intrusive rock units provides evidence of when and how various terranes of the Insular superterrane were assembled to form the western
Canadian Cordillera in Yukon and northern British Columbia. During the Middle to Late Paleozoic the terranes were translated from the Paleo-Arctic Ocean, where they formed, to the Paleo-Pacific Ocean. The Insular terranes are host to numerous mineral
deposits whose generation can now directly be linked to their tectonic evolution. |
| GEOSCAN ID | 293948 |
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