Late Paleozoic assembly of the Alexander-Wrangellia-Peninsular composite terrane, Canadian and Alaskan Cordillera

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 sug-gest 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 marg...

Detrital zircon geochronology along a structural transect across the Kahiltna assemblage in the western Alaska Range: Implications for emplacement of the Alexander-Wrangellia-Peninsular terrane against North America

“…With the advent of the terrane concept (Jones et al, 1977(Jones et al, , 1982Coney and Jones, 1985), it was recognized that deformed Kahiltna assemblage strata separate distinct crustal domains to the south (Wrangellia and Peninsular terranes, which had earlier amalgamated to form the Alexander-Wrangellia-Peninsular terrane; Beranek et al, 2014) and north (Farewell and Yukon composite terranes) and appear to mark a zone of relative movement between those domains. This broad zone of deformation has been termed a "flysch-filled suture" (Jones et al, 1982) or the Alaska Range suture zone (Ridgway et al, 2002).…”

“…Late Jurassic tectonism is interpreted by some as recording a collisional event between the combined Alexander-Wrangellia terranes and the Peninsular terrane (Clift et al, 2005;Rioux et al, 2007;Amato et al, 2013;Moore and Box, 2016) to form the combined Alexander-Wrangellia-Peninsular terrane. However, Beranek et al (2014) argued that the Alexander-Wrangellia-Peninsular terrane was amalgamated earlier in the Permian.…”

“…Following these authors, we refer to the basinal strata as the Kahiltna assemblage and subdivide it based on age and detrital composition. The assemblage is bounded to the southeast by Triassic and older rocks of the Wrangellia terrane and Triassic and Jurassic rocks of the Peninsular terrane (Jones et al, 1977;Nokleberg et al, 1994;Detterman et al, 1996;Rioux et al, 2007;Greene et al, 2010;Beranek et al, 2014). Exposures on the northwest side of the belt for much of its extent are Paleozoic and Mesozoic carbonate and clastic strata of the Farewell terrane (Dumoulin et al, 2018a(Dumoulin et al, , 2018b.…”

Logan Medallist 1. Seeking the Suture: The Coast-Cascade Conundrum

“…West of the northern Coast Mountains, the Alexander terrane contains a record of latest Neoproterozoic -early Paleozoic arc magmatism and deformation and was juxtaposed with Wrangellia, with the boundary between them 'stitched' by Late Carboniferous plutons (301-307 Ma; Gardner et al 1988;Beranek et al 2014). In the Middle and Late Devonian (390-360 Ma) arc-related magmatic activity was initiated in the Quesnellia, Stikinia, Wrangellia and Yukon-Tanana terranes, as well as in strata in southeastern British Columbia considered by most to be outer parts of the Laurentian margin (Piercey et al 2006;their fig.…”

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…Post-collision, slab detachment led to asthenospheric upwelling and partial melting of the thickened crust to produce granitoids in the Meguma Terrane of Nova Scotia (Keppie and Dallmeyer, 1995). Similarly, recent geochemical work on the plutons of the Barnard Glacier suite predicts it was formed due to asthenospheric upwelling from slab detachment after Wrangellia collided with the Alexander composite terrane (Beranek et al, 2014). These magmatic sutures help to modify the accreted terrane crust.…”