Geologic map of the eastern half of the McGrath Quadrangle, Alaska

Bundtzen, Thomas K.; Harris, E. E.; Gilbert, W.G.

doi:10.14509/2549

Cited by 10 publications

(57 citation statements)

References 13 publications

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“…2 and 3) exposes deformed strata of the Dillinger and Mystic subterranes of the Farewell terrane (Dumoulin et al, 2018a(Dumoulin et al, , 2018b. These thin-bedded carbonates and siliciclastic turbidite strata are cut by top-to-the-northwest thrust faults and have been deformed into northwest-vergent overturned folds (Bundtzen et al, 1997; see subsequent section on "Deformation of the Kahiltna assemblage"). Exposed Farewell strata range from Cambrian-Ordovician to Lower Jurassic, with scattered occurrences of Lower Cretaceous (Valanginian) strata (Reed and Nelson, 1980;Dumoulin et al, 2018aDumoulin et al, , 2018b.…”

Section: Older Strata Northwest Of the Kahiltna Assemblagementioning

confidence: 98%

“…), while the quartzose succession has sparse Valanginian, Hauterivian-Barremian, and Cenomanian(?) macrofossil occurrences (Csejtey et al, 1992;Bundtzen et al, 1997;Reed and Nelson, 1980). However, Dumoulin et al (2018b) suggested that some, and perhaps all, of the Valanginian and Hauterivian-Barremian fossil localities along or near the northwestern margin of the northwestern succession are part of the underlying Mystic subterrane of the Farewell terrane, and not the Kahiltna assemblage.…”

Section: ■ Previous Workmentioning

confidence: 99%

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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

et al. 2019

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The Kahiltna assemblage in the western Alaska Range consists of deformed Upper Jurassic and Cretaceous clastic strata that lie between the Alexander-Wrangellia-Peninsular terrane to the south and the Farewell and other pericratonic terranes to the north. Differences in detrital zircon populations and sandstone petrography allow geographic separation of the strata into two different successions, each consisting of multiple units, or petrofacies, with distinct provenance and lithologic characteristics. The northwestern succession was largely derived from older, inboard pericratonic terranes and correlates along strike to the southwest with the Kuskokwim Group. The southeastern succession is characterized by volcanic and plutonic rock detritus derived from Late Jurassic igneous rocks of the Alexander-Wrangellia-Peninsular terrane and mid- to Late Cretaceous arc-related igneous rocks and is part of a longer belt to the southwest and northeast, here named the Koksetna-Clearwater belt. The two successions remained separate depositional systems until the Late Cretaceous, when the northwestern succession overlapped the southeastern succession at ca. 81 Ma. They were deformed together ca. 80 Ma by southeast-verging fold-and-thrust–style deformation interpreted to represent final accretion of the Alexander-Wrangellia-Peninsular terrane along the southern Alaska margin. We interpret the tectonic evolution of the Kahiltna successions as a progression from forearc sedimentation and accretion in a south-facing continental magmatic arc to arrival and partial underthrusting of the back-arc flank of an active, south-facing island-arc system (Alexander-Wrangellia-Peninsular terrane). A modern analogue is the ongoing collision and partial underthrusting of the Izu-Bonin-Marianas island arc beneath the Japan Trench–Nankai Trough on the east side of central Japan.

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Section: Older Strata Northwest Of the Kahiltna Assemblagementioning

confidence: 98%

Section: ■ Previous Workmentioning

confidence: 99%

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

et al. 2019

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“…[6] The Kahiltna assemblage crops out in a >400 km long belt throughout south central and southwestern Alaska (Figures 1 and 2) and has been mainly described from previous studies in the context of regional geologic mapping projects [e.g., Csejtey et al, 1978Csejtey et al, , 1992Reed and Nelson, 1980;Jones et al, 1982;Smith et al, 1988;Bundtzen et al, 1997]. The unit consists of a 3-5 km thick succession of mainly submarine fan strata [e.g., Wallace et al, 1989;Eastham, 2002;Hampton et al, 2007;Kalbas et al, 2007] that represent >45 Myr of continuous clastic sedimentation.…”

Section: Geologic Backgroundmentioning

confidence: 99%

A detrital record of Mesozoic island arc accretion and exhumation in the North American Cordillera: U-Pb geochronology of the Kahiltna basin, southern Alaska

2010

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The stratigraphic record of Mesozoic arc accretion in the North American Cordillera is preserved in a discontinuous belt of clastic strata that are exposed inboard (cratonward) of the allochthonous Wrangellia composite terrane in southern Alaska, western Canada, and Washington State. LA‐ICPMS analyses of eight samples (n = 714 detrital zircon grains) collected at different stratigraphic intervals from the Jurassic‐Cretaceous Kahiltna assemblage in southern Alaska reveals a bulk U‐Pb age distribution of Precambrian‐Mesozoic age grains (Mz 74%, Pz 11%, Pc 15%). A comparison of U‐Pb ages from older to younger stratigraphic intervals within the Kahiltna assemblage reveals three stages of exhumation and basin development during arc accretion. Stages include (1) an initial Late Jurassic–Early Cretaceous pre/early collisional phase during which detritus was derived almost solely from Middle–Late Jurassic and Early Cretaceous magmatic sources of the outboard Wrangellia composite terrane (Mz 100%, Pz 0%, Pc, 0%), (2) a second Early Cretaceous syncollisional phase that reflects the introduction of Paleozoic and Precambrian detritus from the inboard Intermontane belt (Mz 84%, Pz 11%, Pc 5%) and an upsection increase in older detrital zircon grains compared to Mesozoic age grains (Mz 65%, Pz 11%, Pc 24%), and (3) a final Early‐Late Cretaceous late/postcollisional phase that represents continued detrital contributions from Precambrian–Mesozoic source areas (Mz 19%, Pz 22%, Pc 59%) located inboard and outboard of the Kahiltna basin. Similar bulk trends in detrital zircon age populations have been reported from along‐strike, age‐equivalent strata of the Gravina belt (Mz 74%, Pz 20%, Pc 6%) in southeastern Alaska suggesting that similar provenance trends may exist in basins along this >2000 km ‐long collisional zone.

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“…10A and 10B). Sedimentary features, including graded bedding and partial Bouma sequences (Bundtzen et al, 1997), suggest a turbidite origin for this unit. Composition of coarser beds is generally similar to that of sandstone and conglomerate in the Terra Cotta Mountains Sandstone, with a mix of carbonate clasts, quartz, feldspar, and metamorphic and sedimentary lithic grains (Figs.…”

Section: Dillinger Subterrane Stratigraphy and Lithologiesmentioning

confidence: 90%

“…The Farewell terrane (Decker et al, 1994;Bundtzen et al, 1997;Bradley et al, 2003) consists of a Proterozoic basement complex overlain by younger Proterozoic through Mesozoic strata that have been divided into several sequences or subterranes (Fig. 3).…”

Section: Geologic Settingmentioning

confidence: 99%

Neoproterozoic–early Paleozoic provenance evolution of sedimentary rocks in and adjacent to the Farewell terrane (interior Alaska)

et al. 2018

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Geologic map of the eastern half of the McGrath Quadrangle, Alaska

Cited by 10 publications

References 13 publications

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

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

A detrital record of Mesozoic island arc accretion and exhumation in the North American Cordillera: U-Pb geochronology of the Kahiltna basin, southern Alaska

Neoproterozoic–early Paleozoic provenance evolution of sedimentary rocks in and adjacent to the Farewell terrane (interior Alaska)

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