Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner of Healy quadrangle, Alaska

Csejtey, Béla; Nelson, Willis H.; Jones, David L.; Silberling, Norman J.; Dean, RA; Morris, M.S.; Lanphere, Marvin A.; Smith, J. G.; Silberman, Miles L.

doi:10.3133/ofr78558a

Cited by 51 publications

(52 citation statements)

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“…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. All of the plutonic sections define similar geochemical trends (Figures 5 and 6), and the evolved crust in these areas is chemically similar to the middle crust of the Izu-Bonin arc exposed in the Tanzawa plutonic complex (Figures 5 and 6).…”

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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“…[5] This study builds on an existing geochronology data set that is examined in detail later in the paper. The first, quite extensive, studies of the Talkeetna and Chugach mountains, by Csejtey et al [1978] and Winkler et al [1981] reported dozens of hornblende and mica K/Ar ages, revealing that the Talkeetna arc cooled in the Jurassic and that there was significant Tertiary magmatism in the Talkeetna Mountains. Later K/Ar and 40 Ar/ 39 Ar dating by Pavlis [1983], Plafker et al [1989], Onstott et al [1989], Winkler [1992], and Barnett et al [1994] reinforced this data set and revealed an additional significant Late Cretaceous pulse of magmatism in the western Chugach Mountains.…”

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%

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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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Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Finzel

Enkelmann

2017

Geochem Geophys Geosyst

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The Cook Inlet in south‐central Alaska contains the early Oligocene to Recent stratigraphic record of a fore‐arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U‐Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat‐slab subduction on the depositional environments, provenance, and subsidence in fore‐arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat‐slab traversed the entire width of the basin. These mud‐dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat‐slab region continued to cross the basin during Pliocene time, but a change to sandstone‐dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike‐orientation of the down‐going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore‐arc basins.

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Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner of Healy quadrangle, Alaska

Cited by 51 publications

References 3 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

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

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

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