Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska

Winkler, Gary R.; Silberman, Miles L.; Grantz, Arthur; Miller, Ralph L.; MacKevett, E.M.

doi:10.3133/ofr80892a

Cited by 62 publications

(65 citation statements)

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“…The relative proportions of evolved plutons are likely structurally controlled. The crustal sections in the Chugach Mountains and on the Kodiak archipelago are composed of steeply dipping plutonic and volcanic blocks [Connelly and Moore, 1979;Winkler, 1992], leading to thin, faulted layers of evolved midcrustal material. In contrast, some volcanic rocks on the Alaska Peninsula and in the Talkeetna Mountains have shallow to flat dips [Csejtey et al, 1978;Detterman and Reed, 1980], suggesting that these areas represent broad slices through midcrustal plutonic complexes.…”

Section: Felsic Magmatism In Intraoceanic Arcsmentioning

confidence: 99%

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Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs

et al. 2010

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Seismic profiles of several modern arcs have identified thick, low‐velocity midcrustal layers (Vp = 6.0–6.5 km/s) that are interpreted to represent intermediate to felsic plutonic crust. The presence of this silicic crust is surprising given the mafic composition of most primitive mantle melts and could have important implications for the chemical evolution and bulk composition of arcs. However, direct studies of the middle crust are limited by the restricted plutonic exposures in modern arcs. The accreted Talkeetna arc, south central Alaska, exposes a faulted crustal section from residual subarc mantle to subaerial volcanic rocks of a Jurassic intraoceanic arc and is an ideal place to study the intrusive middle crust. Previous research on the arc, which has provided insight into a range of arc processes, has principally focused on western exposures of the arc in the Chugach Mountains. We present new U‐Pb zircon dates, radiogenic isotope data, and whole‐rock geochemical analyses that provide the first high‐precision data on large intermediate to felsic plutonic exposures on Kodiak Island and the Alaska Peninsula. A single chemical abrasion–thermal ionization mass spectrometry analysis from the Afognak pluton yielded an age of 212.87 ± 0.19 Ma, indicating that the plutonic exposures on Kodiak Island represent the earliest preserved record of Talkeetna arc magmatism. Nine new dates from the extensive Jurassic batholith on the Alaska Peninsula range from 183.5 to 164.1 Ma and require a northward shift in the Talkeetna arc magmatic axis following initial emplacement of the Kodiak plutons, paralleling the development of arc magmatism in the Chugach and Talkeetna mountains. Radiogenic isotope data from the Alaska Peninsula and the Kodiak archipelago range from ɛNd(t) = 5.2 to 9.0 and 87Sr/86Srint = 0.703515 to 0.703947 and are similar to age‐corrected data from modern intraoceanic arcs, suggesting that the evolved Alaska Peninsula plutons formed by extensive differentiation of arc basalts with little or no involvement of preexisting crustal material. The whole‐rock geochemical data and calculated seismic velocities suggest that the Alaska Peninsula represents an analogue for the low‐velocity middle crust observed in modern arcs. The continuous temporal record and extensive exposure of intermediate to felsic plutonic rocks in the Talkeetna arc indicate that evolved magmas are generated by repetitive or steady state processes and play a fundamental role in the growth and evolution of intraoceanic arcs.

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Section: Felsic Magmatism In Intraoceanic Arcsmentioning

confidence: 99%

“…Figure 1, and the rock types follow the legend in Figure 2. The geologic maps are modified from Csejtey et al [1978], Winkler et al [1981], Winkler [1992], Wilson et al [1998], and the reference given in Figure 2. modern arc [Calvert et al, 2008].…”

Section: Felsic Magmatism In Intraoceanic Arcsmentioning

confidence: 99%

Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs

et al. 2010

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“…This effective erosion rate, _ E, is averaged over the retreat period and the entire glacierized area, A: For the 1000 km 2 catchment, we use an average bedrock density, ρ rock , of 2700 kg m −3 , a reasonable mean value for the deformed metasedimentary and sedimentary rocks that dominate the Columbia Glacier Basin bedrock (Winkler, 1992). From our 1-2 m long sediment cores, we measured a dry bulk density, ρ sed , of 1000 ± 100 kg m −3 .…”

Section: Effective Erosion Ratementioning

confidence: 99%

Observations and modeling of fjord sedimentation during the 30 year retreat of Columbia Glacier, AK

et al. 2016

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ABSTRACT. To explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 10 8 m 3 of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ∼5 mm a −1 of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of the glacier surface over a known subglacial deep basin. Because variations in subglacial sediment storage can impact glacial sediment flux, in addition to changes in climate, erosion rate and glacier dynamics, the interpretation of climatic changes based on the sediment record is more complex than generally assumed.

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“…Beneath the Border Ranges fault system lie Late Triassic blueschist, Cretaceous mélange and turbidites of the Chugach terrane [Plafker et al, 1994]. A klippe of arc plutonic rocks south of the Border Ranges fault zone in the Klanelneechena area [Winkler et al, 1981] has been correlated with the Talkeetna arc. The Talkeetna arc is overlain by a sequence of Jurassic to Oligocene sedimentary and volcanic rocks and intruded by a variety of Late Cretaceous to Oligocene rocks reflecting Jurassic through Recent plate convergence [Plafker et al, 1994;Trop and Ridgeway, 2007].…”

Section: Introductionmentioning

confidence: 99%

“…Questionable ages are shown in italics. Ages are from this study except for the following: B4, Barnett et al [1994]; DL, Drake and Layer [2001]; C, Csejtey et al [1978]; LN, Little and Naeser [1989]; O9, Onstott et al [1989]; P3, Pavlis [1983]; P9, Plafker et al [1989]; SO, Sisson and Onstott [1986]; W1, Winkler et al [1981]; W2, Winkler [1992]. Thick lines are faults, and thin lines are depositional and intrusive contacts.…”

Section: Introductionmentioning

confidence: 99%

Thermochronology of the Talkeetna intraoceanic arc of Alaska: Ar/Ar, U‐Th/He, Sm‐Nd, and Lu‐Hf dating

et al. 2011

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[1] As one of two well-exposed intraoceanic arcs, the Talkeetna arc of Alaska affords an opportunity to understand processes deep within arcs. This study reports new Lu-Hf and Sm-Nd garnet ages, 40 Ar/ 39 Ar hornblende, mica and whole-rock ages, and U-Th/He zircon and apatite ages from the Chugach Mountains, Talkeetna Mountains, and Alaska Peninsula, which, in conjunction with existing geochronology, constrain the thermal history of the arc. The oldest U-Th/He zircon ages are ∼137 to 129 Ma, indicating no Cenozoic regional heating above ∼180°C. Although the signal is likely complicated by Cretaceous and Oligocene postarc magmatism, the aggregate thermochronology record indicates that the thermal history of the Talkeetna arc was spatially variable. Onedimensional finite difference thermal models show that this kind of spatial variability is inherent to intraoceanic arcs with simple construction histories. Citation: Hacker,

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Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska

Cited by 62 publications

References 0 publications

Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs

Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs

Observations and modeling of fjord sedimentation during the 30 year retreat of Columbia Glacier, AK

Thermochronology of the Talkeetna intraoceanic arc of Alaska: Ar/Ar, U‐Th/He, Sm‐Nd, and Lu‐Hf dating

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