Map showing pre-Cenozoic tectonostratigraphic terranes of southeastern Alaska and adjacent areas

Berg, Henry C.; Jones, David L.; Coney, Peter J.

doi:10.3133/ofr781085

Cited by 58 publications

(52 citation statements)

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“…1A) is itself a composite terrane that has been subdivided into the Craig and Admiralty subterranes based on apparent differences in their pre-Permian geological histories and stratigraphic assemblages (Berg et al, 1978;Gehrels and Saleeby, 1987;Monger and Berg, 1987). The Craig subterrane (Fig.…”

Section: Alexander Terranementioning

confidence: 98%

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

Beranek

Staal

McClelland

et al. 2014

Geological Society of America Bulletin

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Late Paleozoic assembly of the AlexanderWrangellia-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 WrangelliaPeninsular 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 AlexanderWrangellia-Peninsular composite terrane took place along a convergent margin t...

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Section: Alexander Terranementioning

confidence: 98%

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

Beranek

Staal

McClelland

et al. 2014

Geological Society of America Bulletin

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“…These include the Constitution Formation (Vance 1977;Brandon 1980), "Decatur terrane" (Whetten et al 1978), the Spieden Group (Johnson 1981) in the San Juan Islands, the Nooksack Group (Misch 1966) in the North Cascades, and the Pacific Rim complex (Muller 1977a,b) on the west coast of Vancouver Island (Fig. greenstonk, alongthe Pacific margin of North America. These assemblages, including the Chugach terrane (Berg et al 1978) in south Alaska and the Franciscan Complex in California, are generally interpreted to have accumulated along an active convergent margin near a volcano-plutonic source area supplying voluminous terrigenous clastic decritus (e.g., Dickinson 1976). Within this broadly convergent setting, however, sediments theoretically could have been deposited in several sedimentologically distinctive environments such as trench, fore-arc basin, or trench-slope basin, or they could have been scraped off a descending plate and incorporated into a developing accretionary wedge.…”

Section: Tectonic Setting Of Deformation and Metamorphismmentioning

confidence: 99%

Structure, petrology, and tectonic history of the Leech River complex northwest of Victoria, Vancouver Island

Fairchild¹,

Cowan²

1982

Can. J. Earth Sci.

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The Leech River complex 45 km northwest of Victoria consists of metamorphosed pelitic rocks, sandstone, and minor volcanic rocks, chert, and conglomerate of probable Late Jurassic to Cretaceous age. The assemblage experienced two similar deformational events during which regional shortening induced macroscopic east-plunging folds and related coaxial, mesoscopic linear structures, parasitic folds, and axial-plane cleavages. Fragmentation along the developing cleavages disrupted layering and eventually led to transposition during both events. Regional, progressive, low-pressure greenschist-to amphibolite-facies (andalusite-staurolite-biotite) metamorphism began during the first deformation and extended into the waning stages of the second. Intrusion of composite felsic sills was synchronous with deformation and metamorphism, which concluded about 39-41 Ma, according to K-Ar data. The Leech River fault, which forms the southern boundary of the complex, is a zone of two to four subparallel faults. All are relatively straight, narrow faults that appear to dip steeply. This structure is interpreted to be a left-lateral strike-slip fault, active exclusively after the 39-41 Ma conclusion of metamorphism and deformation.The Leech River complex originally may have accumulated somewhere along a late Mesozoic convergent margin, but there is no evidence that it either constitutes a subduction complex per se or was metamorphosed in such a setting in early Tertiary time. The Leech River complex is interpreted to be allochthonous with respect to the bulk of Vancouver Island, since neither older rocks of the Insular Belt (Wrangellia) to the north nor coeval rocks in northwestern Washington record the early Tertiary deformations and synkinematic low-pressure metamorphism. The complex apparently was derived from a cryptic terrane to the west and emplaced against Vancouver Island by left-lateral slip on the San Juan fault after 39-41 Ma.Le complexe Leech River, A 45 km au nord-ouest de Victoria, est composC de roches p6litiques mCtamorphostes, de grks, et en importance secondaire de roches volcaniques, de chert et conglomCrat probablement d'lge Jurassique sup6rieur i CdtacC.L'assemblage A subi deux phases analogues de dkfomation entrainant un rCtrCcissement dgional produisant des plis macroscopiques de plongCe vers I'est avec des axes parallkles, des structures IinCaires mCsoscopiques, des plis parasites et des clivages ardoisiers axiaux. La fragmentation causCe par les clivages a rompu la stratification et a provoquC Cventuellement uQe transposition durant les deux phases de dkformation. I1 est apparu pendant la premikre phase de deformation un faciks mktamorphique regional, progressif et de basse-pression, allant des schistes verts A celui de I'amphibolite (andalousite-staurotide-biotite) dont le developpement s'est poursuivi jusqu'i la @riode de dicroissance de la deuxikme dCfomation. Des filons-couches composites de roches felsitiques ont Ctt inject& lors de la dkformation et pendant le mCtamorphisme, et dont la fin des activitC...

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“…The northern part of the belt is in the Admiralty subterrane of the Alexander tectonostratigraphic terranel/ (figure 1; Berg, Jones, and Coney, 1978;Berg, 1979), and the southern part is in the Annette subterrane of the Alexander terrane. We interpret this belt as a regional metallogenic province containing stratabound volcanogenic Zn-Pb-Ag(-Cu-Au)-bearing massive sulfide and related barite deposits in deformed and metamorphosed Upper Triassic strata.…”

Section: Regional Implicationsmentioning

confidence: 99%

Map showing pre-Cenozoic tectonostratigraphic terranes of southeastern Alaska and adjacent areas

Cited by 58 publications

References 0 publications

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

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

Structure, petrology, and tectonic history of the Leech River complex northwest of Victoria, Vancouver Island

Upper Triassic volcanogenic Zn-Pb-Ag(-Cu-Au) mineral deposits near Petersburg, Alaska

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