Bedrock geologic map of the eastern Denali Highway area, Mount Hayes, Healy, and Talkeetna Mountains quadrangles, Alaska

Twelker, Evan; Waldien, Trevor S.; Newberry, R. J.; Freeman, L. K.; Sicard, K.R.; Lande, Lauren; Wypych, Alicja; Reioux, D.A.; Bachmann, E.N.

doi:10.14509/30469

Cited by 3 publications

(11 citation statements)

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“…(2018), Twelker et al. (2020), Waldien et al. (2021), and our new mapping near the headwaters of the Maclaren River.…”

Section: Introductionmentioning

confidence: 51%

“…Mapping focused on alongstrike correlation of major structures and bedrock units between the eastern Alaska Range and Clearwater mountains. Here, we present a new bedrock geologic map (Figure 2), compiled from the new mapping and prior mapping by Turner and Smith (1974), Smith (1981), Mooney (2010), Waldien et al (2018), Twelker et al (2020.…”

Section: Geologic Mappingmentioning

confidence: 99%

“…Triassic Nikolai flood basalt strata unconformably overly the Paleozoic rocks in the region (Greene et al., 2008; 2010; Twelker et al., 2020). Nikolai strata and associated intrusions yield crystallization ages of 225–230 Ma (Bittenbender et al., 2007; Greene et al., 2010; Twelker et al., 2020; Waldien et al., 2021).…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…Carbonate strata containing Early Permian fossils unconformably overly the Skolai arc rocks (Bond, 1973, 1976; Nokleberg, Aleinikoff, Dutro, et al., 1992; Richter & Dutro, 1975) and may record cessation of Skolai arc magmatism in the Late Pennsylvanian (e.g., Beranek et al., 2014; Israel et al., 2014). Triassic Nikolai flood basalt strata unconformably overly the Paleozoic rocks in the region (Greene et al., 2008; 2010; Twelker et al., 2020). Nikolai strata and associated intrusions yield crystallization ages of 225–230 Ma (Bittenbender et al., 2007; Greene et al., 2010; Twelker et al., 2020; Waldien et al., 2021).…”

Section: Geologic Backgroundmentioning

confidence: 99%

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Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

2021

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Terrane accretion introduces irregular geometry and allochthonous material to obliquely convergent margins, which create opportunities to quantify strike-slip displacement along otherwise margin-parallel fault systems. We present new bedrock geologic mapping and U-Pb and 40 Ar/ 39 Ar geochronology from the Alaska Range suture zone in the eastern Alaska Range, which confirm a longhypothesized correlation between the Maclaren Glacier metamorphic belt (Alaska, USA) and the Kluane metamorphic assemblage (Yukon Territory, Canada) across the right-lateral Denali fault. The new data inform a palinspastic reconstruction showing that the dissected metamorphic belts and associated plutons record ~480 km of dextral displacement along the Denali fault since ca. 52 Ma. Before strike-slip separation, the Maclaren-Kluane schist formed by west-vergent forearc underplating in the waning stage of the ca. 100-90 Ma arc built upon the Yukon-Tanana terrane. The prograde structural and metamorphic evolution of the Maclaren-Kluane schist records the final collision of the Wrangellia composite terrane at ca. 75-65 Ma along a set of east-dipping thrust shear zones, which we infer to record the polarity of the Late Cretaceous plate boundary between the composite terrane and North America. Paleogene extension partially exhumed the schists to the upper crust and may be a consequence of regionally distributed strike-slip faulting at that time. Localization of the modern Denali fault after ca. 52 Ma dismembered the schists and four neighboring belts of plutonic, metasedimentary, and volcanic rocks. The transition to Yakutat oblique flat slab subduction at ca. 30-25 Ma marks the onset of transpressional deformation in the Denali fault system, which reactivated Late Cretaceous collisional structures bounding the Maclaren schist. Neogene reactivation of the Totschunda fault reduced strike-slip motion on the Denali fault east of the Denali-Totschunda intersection and continues to transfer residual plate boundary slip onto the Denali fault west of the intersection. Key outcomes of our synthesis include: (a) Much of the ~480 km of displacement on the Denali fault accumulated after strike-slip on the neighboring Tintina and Border Ranges fault systems had largely shut down; (b) The modern Denali fault system should not be grouped with strike-slip faults credited with large-scale margin-parallel transport of Cordilleran terranes in the Cretaceous. Instead, a poorly understood proto-Denali fault system may be a candidate for large-scale Cretaceous translation; and (c) the longevity (≥33 Myr) of the highly localized Denali fault master strand (≤1 km wide) implies that it occupies a major mechanical boundary that penetrates the lithosphere.Plain Language Summary Many of the rocks that make up present-day western Canada and southern Alaska did not form as part of North America. Instead, most formed as coherent island chains (called terranes), collided with North America, and then slid northward along fault systems to their present location. The timing of...

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“…(2018), Twelker et al. (2020), Waldien et al. (2021), and our new mapping near the headwaters of the Maclaren River.…”

Section: Introductionmentioning

confidence: 51%

Section: Geologic Mappingmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

See 2 more Smart Citations

Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

2021

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“… Bedrock geologic map of the study area simplified from Twelker et al. (2020) and Waldien, Roeske, Benowitz, et al. (2021) showing the locations of thermochronology samples (red circles), thermochronology sample transects discussed in the text, and the footprints of Figures 3 and 4 (black boxes).…”

Section: Geologic Backgroundmentioning

confidence: 99%

Suture Reactivation, Slip Partitioning, and a Protracted Strike‐Slip Rate Gradient in the Denali Fault System, Southern Alaska, USA

Waldien,

Roeske,

Chatterjee

et al. 2023

Tectonics

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Active strike‐slip fault systems commonly display along‐strike Quaternary slip rate gradients associated with fault bends and splay faults, which generate surface uplift by dip‐slip faulting or distributed “off fault” deformation. By analogy, the documentation of long‐term (107 yr) slip gradients on some continental strike‐slip fault systems implies long‐term coevolution of strike‐slip and dip‐slip fault systems. Here we leverage the observed ≥33 Myr right‐lateral slip gradient on the Denali fault, Alaska, USA to investigate the role of splay thrust systems in accommodating the slip gradient. We focus on the Broxson Gulch thrust system, which splays southwestward from the Denali fault in the eastern Alaska Range. Apatite and zircon (U‐Th)/He and fission‐track cooling ages from metasedimentary and metaplutonic rocks intersected by the thrust system record an along‐strike decrease in cooling ages commensurate with an increase in late Oligocene‐Neogene bedrock exhumation and shortening with proximity to the Denali fault. The dominant structure in the Broxson Gulch thrust system is the Valdez Creek fault, which is an upper crustal reactivation of the Valdez Creek shear zone–the main Late Cretaceous suture between western North America and outboard accreted arc terranes. After reactivation of the Valdez Creek shear zone at ca. 30 Ma, the thrust system grew by south‐vergent imbrication of the upper crust along thrust and reverse faults until at least 6 Ma. Incorporating results from the Broxson Gulch thrust system into the regional structural evolution of the Denali fault system reveals significant spatiotemporal heterogeneity in shortening adjacent to the Denali fault. Moreover, nearly all of the late Oligocene‐Neogene shortening south of the Denali fault was focused along reactivated terrane boundaries inherited from Mesozoic assembly of the North American Cordillera, and the spatial distribution of the inherited structures appears to control slip partitioning behavior of the Denali fault system across time scales ranging from 101 (historic seismicity) to 107 yr. The slip partitioning behavior of the Denali fault system highlights the mechanical importance of inherited structures leading to protracted shortening on splay thrust systems, which siphon slip from the master strike‐slip fault. We contend that the weakness of nearby reactivated terrane boundaries should be considered among other mechanisms commonly evoked to explain the partitioning behavior of continental strike‐slip fault systems (e.g., stress field rotation, obliquity angle, and strength of master strike‐slip fault).

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Oligocene-Neogene lithospheric-scale reactivation of Mesozoic terrane accretionary structures in the Alaska Range suture zone, southern Alaska, USA

et al. 2020

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Terrane accretion forms lithospheric-scale fault systems that commonly experience long and complex slip histories. Unraveling the evolution of these suture zone fault systems yields valuable information regarding the relative importance of various upper crustal structures and their linkage through the lithosphere. We present new bedrock geologic mapping and geochronology data documenting the geologic evolution of reactivated shortening structures and adjacent metamorphic rocks in the Alaska Range suture zone at the inboard margin of the Wrangellia composite terrane in the eastern Alaska Range, Alaska, USA. Detrital zircon uranium-lead (U-Pb) age spectra from metamorphic rocks in our study area reveal two distinct metasedimentary belts. The Maclaren schist occupies the inboard (northern) belt, which was derived from terranes along the western margin of North America during the mid- to Late Cretaceous. In contrast, the Clearwater metasediments occupy the outboard (southern) belt, which was derived from arcs built on the Wrangellia composite terrane during the Late Jurassic to Early Cretaceous. A newly discovered locality of Alaska-type zoned ultramafic bodies within the Clearwater metasediments provides an additional link to the Wrangellia composite terrane. The Maclaren and Clearwater metasedimentary belts are presently juxtaposed by the newly identified Valdez Creek fault, which is an upper crustal reactivation of the Valdez Creek shear zone, the Late Cretaceous plate boundary that initially brought them together. 40Ar/39Ar mica ages reveal independent post-collisional thermal histories of hanging wall and footwall rocks until reactivation localized on the Valdez Creek fault after ca. 32 Ma. Slip on the Valdez Creek fault expanded into a thrust system that progressed southward to the Broxson Gulch fault at the southern margin of the suture zone and eventually into the Wrangellia terrane. Detrital zircon U-Pb age spectra and clast assemblages from fault-bounded Cenozoic gravel deposits indicate that the thrust system was active during the Oligocene and into the Pliocene, likely as a far-field result of ongoing flat-slab subduction and accretion of the Yakutat microplate. The Valdez Creek fault was the primary reactivated structure in the suture zone, likely due to its linkage with the reactivated boundary zone between the Wrangellia composite terrane and North America in the lithospheric mantle.

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Bedrock geologic map of the eastern Denali Highway area, Mount Hayes, Healy, and Talkeetna Mountains quadrangles, Alaska

Cited by 3 publications

References 0 publications

Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

Suture Reactivation, Slip Partitioning, and a Protracted Strike‐Slip Rate Gradient in the Denali Fault System, Southern Alaska, USA

Oligocene-Neogene lithospheric-scale reactivation of Mesozoic terrane accretionary structures in the Alaska Range suture zone, southern Alaska, USA

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