Regional patterns of Mesozoic-Cenozoic magmatism in western Alaska revealed by new U-Pb and 40Ar/39Ar ages

Bradley, Dwight C.; Miller, Marti L.; Friedman, Richard M.; Layer, Paul W.; Bleick, Heather A.; Jones, James V.; Box, S. E.; Karl, Susan M.; Shew, Nora B.; White, Timothy S.; Till, Alison B.; Dumoulin, Julie A.; Bundtzen, Thomas K.; O’Sullivan, Paul B.; Ullrich, Thomas

doi:10.3133/pp1814d

Cited by 3 publications

(11 citation statements)

References 18 publications

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“…We sampled dacitic volcanic rocks from the northern end of the field; these rocks yielded a zircon U-Pb age of 40.9 ± 0.7 Ma (E8; Table 1), consistent with the age of the intrusion to the south and indicating that they were co-magmatic. In the Sheep Creek volcanic field to the northwest, Bradley et al (2017) reported a zircon U-Pb age of 56.1 ± 1.9 Ma (01ADw7a; Table 1) that is consistent with the K-Ar ages of the nearby Sheep Creek intrusion (Solie et al, 1991a). Bradley et al (2017) also reported a zircon U-Pb age of 42.8 ± 0.5 Ma (01ADw8A) for a felsic tuff from the highest point at the southern end of the same field, indicating that the Sheep Creek volcanic field was emplaced during two magmatic episodes.…”

Section: Research Papersupporting

confidence: 55%

“…In the Sheep Creek volcanic field to the northwest, Bradley et al (2017) reported a zircon U-Pb age of 56.1 ± 1.9 Ma (01ADw7a; Table 1) that is consistent with the K-Ar ages of the nearby Sheep Creek intrusion (Solie et al, 1991a). Bradley et al (2017) also reported a zircon U-Pb age of 42.8 ± 0.5 Ma (01ADw8A) for a felsic tuff from the highest point at the southern end of the same field, indicating that the Sheep Creek volcanic field was emplaced during two magmatic episodes. Solie et al (1991a) reported K-Ar ages ranging from 49.0 ± 6.8 Ma to 41.7 ± 2.6 Ma for mafic and intermediate volcanic rocks from the field.…”

Section: Research Papersupporting

confidence: 55%

“…24 Ma on aegirine augite from peralkaline granite (Gilbert et al, 1988). Bradley et al (2017) dated zircon from granite exposed in the northern end of the pluton at 31.8 ± 0.4 Ma (11ADw117a; Table 1), and we determined zircon U-Pb ages of 31.6 ± 0.4 Ma and 30.8 ± 0.5 Ma for samples from the western and eastern sides of the pluton (EO4 and EO5; Figs. 2 and 4; Table 1).…”

Section: Latest Eocene and Oligocene (Eo; Ca 35-27 Ma) Suitementioning

confidence: 93%

“…4; Wilson et al, 2015). Bradley et al (2017) reported a zircon date of 56.1 ± 1.9 Ma (01ADw7a ; Table 1) for felsic tuff from the Sheep Creek volcanic field in the northern part of the project area, indicating that volcanic activity associated with this magmatic suite was widespread, though it is not otherwise observed west of the Tordrillo Mountains. On the western side of the study area, the Paleocene Tired Pup batholith underlies a large part of the Revelation Mountains (RM in Fig.…”

Section: Research Papermentioning

confidence: 99%

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Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and 40Ar/39Ar geochronology

et al. 2020

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New U-Pb and 40Ar/39Ar ages integrated with geologic mapping and observations across the western Alaska Range constrain the distribution and tectonic setting of Cretaceous to Oligocene magmatism along an evolving accretionary plate margin in south-central Alaska. These rocks were emplaced across basement domains that include Neoproterozoic to Jurassic carbonate and siliciclastic strata of the Farewell terrane, Triassic and Jurassic plutonic and volcanic rocks of the Peninsular terrane, and Jurassic and Cretaceous siliciclastic strata of the Kahiltna assemblage. Plutonic rocks of different ages also host economic mineralization including intrusion-related Au, porphyry Cu-Mo-Au, polymetallic veins and skarns, and peralkaline intrusion-related rare-earth elements. The oldest intrusive suites were emplaced ca. 104–80 Ma into the Peninsular terrane only prior to final accretion. Deformation of the northern Kahiltna succession and underlying Farewell terrane occurred at ca. 97 Ma, and more widespread deformation ca. 80 Ma involved south-vergent folding and thrusting of the Kahiltna assemblage that records collisional accretion of the Peninsular-Wrangellia terrane and juxtaposition of sediment wedges formed on the inboard and outboard terranes. More widespread magmatism ca. 75–55 Ma occurred in two general pulses, each having distinct styles of localized deformation. Circa 75–65 Ma plutons were emplaced in a transpressional setting and stitch the accreted Peninsular and Wrangellia terranes to the Farewell terrane. Circa 65–55 Ma magmatism occurred across the entire range and extends for more than 200 km inboard from the inferred position of the continental margin. The Paleocene plutonic suite generally reflects shallower emplacement depths relative to older suites and is associated with more abundant andesitic to rhyolitic volcanic rocks. Deformation ca. 58–56 Ma was concentrated along two high-strain zones, the most prominent of which is 1 km wide, strikes east-northeast, and accommodated dextral oblique motion. Emplacement of widespread intermediate to mafic dikes ca. 59–51 Ma occurred before a notable magmatic lull from ca. 51–44 Ma reflecting a late Paleocene to early Eocene slab window. Magmatism resumed ca. 44 Ma, recording the transition from slab window to renewed subduction that formed the Aleutian-Meshik arc to the southwest. In the western Alaska Range, Eocene magmatism included emplacement of the elongate north-south Merrill Pass pluton and large volumes of ca. 44–37 Ma andesitic flows, tuffs, and lahar deposits. Finally, a latest Eocene to Oligocene magmatic pulse involved emplacement of a compositionally variable but spatially concentrated suite of magmas ranging from gabbro to peralkaline granite ca. 35–26 Ma, followed by waning magmatism that coincided with initiation of Yakutat shallow-slab subduction. Cretaceous to Oligocene magmatism throughout the western Alaska Range collectively records terrane accretion, translation, and integration together with evolving subduction dynamics that have shaped the southern Alaska margin since the middle Mesozoic.

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Section: Research Papersupporting

confidence: 55%

Section: Research Papersupporting

confidence: 55%

Section: Latest Eocene and Oligocene (Eo; Ca 35-27 Ma) Suitementioning

confidence: 93%

Section: Research Papermentioning

confidence: 99%

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Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and 40Ar/39Ar geochronology

et al. 2020

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“…15). In the Kuskokwim basin, the timing of deformation is constrained by the youngest marine fossils of the deformed strata (Turonian: 93.9-89.8 Ma; Elder and Box, 1992;Walker et al, 2018) and the oldest ages of unconformably overlying volcanic rocks (74.3 ± 2.2 Ma by 40 Ar/ 39 Ar dating; Box et al, 1993) or crosscutting dikes (U-Pb zircon SHRIMP-RG age of 80.2 ±1.3 Ma; Bradley et al, 2017). In the Yukon-Koyukuk basin, deformed Turonian strata are overlain by lavas and crosscut by hypabyssal intrusive rocks, the oldest K-Ar age of which is 68.8 ± 3 Ma (Patton and Moll-Stalcup, 1996).…”

Section: Far-field Deformation Effects In Interior Alaskamentioning

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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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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Supplemental Material: Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and <sup>40</sup>Ar/<sup>39</sup>Ar geochronology

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2022

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Regional patterns of Mesozoic-Cenozoic magmatism in western Alaska revealed by new U-Pb and 40Ar/39Ar ages

Cited by 3 publications

References 18 publications

Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and 40Ar/39Ar geochronology

Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and 40Ar/39Ar geochronology

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

Supplemental Material: Cretaceous to Oligocene magmatic and tectonic evolution of the western Alaska Range: Insights from U-Pb and <sup>40</sup>Ar/<sup>39</sup>Ar geochronology

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