The Alaska Wrangell Arc: ~30 Ma of subduction‐related magmatism along a still active arc‐transform junction

Brueseke, Matthew E.; Benowitz, Jeffrey A.; Trop, Jeffrey M.; Davis, Kailyn N.; Berkelhammer, Samuel E.; Layer, Paul W.; Morter, Bethany K.

doi:10.1111/ter.12369

Cited by 41 publications

(83 citation statements)

References 40 publications

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“…An alternative source of the ca. 30-29 Ma grains is far-traveled volcanic ash air fall from the oldest phase of the Wrangell arc (Richter et al, 1990;Brueseke et al, 2019) or undocumented volcanic edifices related to the Denali fault Oligocene dike swarms (this study).…”

Section: ■ Colorado Creek Sedimentary Provenance and Denali Fault Dismentioning

confidence: 76%

“…Latest Cretaceous to Holocene plate convergence included persistent subduction of oceanic crust, including subduction of the Yakutat micro plate since ca. 30 Ma (Finzel et al, 2011;Brueseke et al, 2019). The Yakutat microplate is interpreted as an oceanic plateau that has been subducting at a shallow angle beneath Alaska, reaching a maximum geophysically imaged depth of ~100-150 km beneath the Alaska Range (Stachnik et al, 2004;Eberhart-Philips et al, 2006).…”

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confidence: 99%

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Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

et al. 2019

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The Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40Ar/39Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40Ar/39Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (e.g., high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40Ar/39Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate ∼150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible. Together, the dike swarms and fluvial strata are interpreted to record Oligocene strike-slip movement along the Denali fault system, coeval with strike-slip basin development along other segments of the fault. Diking and sedimentation occurred just prior to the onset of rapid and persistent exhumation ca. 25 Ma across the Alaska Range. This phase of reactivation of the suture zone is interpreted to reflect the translation along and convergence of southern Alaska across the Denali fault driven by highly coupled flat-slab subduction of the Yakutat microplate, which continues to accrete to the southern margin of Alaska. Furthermore, a change in Pacific plate direction and velocity at ca. 25 Ma created a more convergent regime along the apex of the Denali fault curve, likely contributing to the shutting off of near-fault extension-facilitated arc magmatism along this section of the fault system and increased exhumation rates.

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Section: ■ Colorado Creek Sedimentary Provenance and Denali Fault Dismentioning

confidence: 76%

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confidence: 99%

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

et al. 2019

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“…In addition, the steep orientation of the slab, which resulted from the collision (Figure 1b), may disrupt convection or dehydration processes in the mantle wedge by reducing the surface area available for fluid flux at depth. A corollary to this latter hypothesis is that the increased surface area available for fluid flux over a flat slab increases the size and volume of volcanism, which has been suggested by Brueseke et al (2019) in Southcentral Alaska. Regardless of which of these effects may apply, the location of thee volcanoes (Figure 1a) suggests that magma ascent south of Fiordland is controlled by the Hauroko Fault, which may be similar in scale to the faults we describe.…”

Section: Return To Strike-slip Motion On Trench-parallel Faultsmentioning

confidence: 94%

The Age and Origin of Miocene‐Pliocene Fault Reactivations in the Upper Plate of an Incipient Subduction Zone, Puysegur Margin, New Zealand

et al. 2019

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Structural observations and 40Ar/39Ar geochronology on pseudotachylyte, mylonite, and other fault zone materials from Fiordland, New Zealand, reveal a multistage history of fault reactivation and uplift above an incipient ocean‐continent subduction zone. The integrated data allow us to distinguish true fault reactivations from cases where different styles of brittle and ductile deformation happen together. Five stages of faulting record the initiation and evolution of subduction at the Puysegur Trench. Stage 1 normal faults (40–25 Ma) formed during continental rifting prior to subduction. These faults were reactivated as dextral strike‐slip shear zones when subduction began at ~25 Ma. The dextral shear zones formed part of a transpressional regime (Stage 2, 25–10 Ma) that included minor reverse motion and modest uplift above the leading edge of the subducting slab as it propagated below Fiordland. At 8–7 Ma (Stage 3), trench‐parallel faults accommodated the first and only episode of pure reverse motion. Reconstructions confirm that these faults formed when the slab reached mantle depths and collided with previously subducted crust. At 5–4 Ma (Stage 4), trench‐parallel faults accommodated oblique‐reverse motion when an oceanic ridge collided obliquely with the Puysegur Trench. Stages 3 and 4 both accelerated rock uplift and topographic growth in short pulses. A return to strike‐slip motion occurred after ~4 Ma (Stage 5) when deformation localized onto the Alpine Fault. These results highlight how the rock record of faulting links displacements occurring at Earth's surface to events occurring both at the trench and deep within the lithosphere during subduction.

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“…We suggest Kluane Ranges Phase III transpression is the far-field response to Yakutat microplate subduction and collision. Flat-slab subduction of that Yakutat terrane began by~35-30 Ma, with transition to microplate collision at~15-12 Ma (Figure 9c (Figure 9a; Brueseke et al, 2019;Richter et al, 1990). From~18-11 Ma, lavas erupted along "leaky" strike-slip and normal faults with MORB-like signatures, suggesting a change in magma reservoir and possible asthenospheric upwelling following northwestward migration of the slab edge (Figure 9a; Richter et al, 1990;Skulski et al, 1992).…”

Section: Phase IIImentioning

confidence: 99%

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

et al. 2019

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Exhumation and landscape evolution along strike‐slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U‐Th)/He (He), zircon He, apatite fission‐track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within ~26–4, ~110–12, ~94–28, and ~137–83 Ma, respectively. A new zircon U‐Pb date of 113.9 ± 1.7 Ma (2σ) complements existing geochronology and aids in interpretation of low‐temperature thermochronometry data patterns. Samples ≤2 km southwest of the EDFZ trace yield the youngest thermochronometry dates. Multimethod thermochronometry, zircon He date‐effective U patterns, and thermal history modeling reveal rapid cooling ~95–75 Ma, slow cooling ~75–30 Ma, and renewed rapid cooling ~30 Ma to present. The magnitude of net surface uplift constrained by published paleobotanical data, exhumation, and total surface uplift from ~30 Ma to present are ~1, ~2–6, and ~1–7 km, respectively. Exhumation is highest closest to the EDFZ trace but substantially lower than reported for the central Denali fault zone. We infer exhumation and elevation changes associated with ~95–75 Ma terrane accretion and EDFZ activity, relief degradation from ~75–30 Ma, and ~30 Ma to present exhumation and surface uplift as a response to flat‐slab subduction and transpressional deformation. Integrated results reveal new constraints on landscape evolution within the Kluane Ranges directly tied to the EDFZ during the last ~100 Myr.

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The Alaska Wrangell Arc: ~30 Ma of subduction‐related magmatism along a still active arc‐transform junction

Cited by 41 publications

References 40 publications

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

The Age and Origin of Miocene‐Pliocene Fault Reactivations in the Upper Plate of an Incipient Subduction Zone, Puysegur Margin, New Zealand

Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

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