The geophysical character of southern Alaska—Implications for crustal evolution

Saltus, Richard W.; Hudson, Travis; Wilson, Frederic H.

doi:10.1130/2007.2431(01)

Cited by 25 publications

(33 citation statements)

References 32 publications

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“…Our 3‐D reference model is essentially the 1‐D model, but stretched and compressed according to a more realistic Moho surface that we describe in section S1. The Moho depth (below sea level) ranges from 11 km under the Pacific plate to 48 km beneath Cook Inlet [ Saltus et al , ]. For regions where the estimated Moho is shallower than the Moho of the 1‐D model (31 km), we compress the 1‐D crustal model and stretch the AK135 mantle model.…”

Section: Methodssupporting

confidence: 58%

“…The Talkeetna formation (e.g., Figure ) and associated ultramafic rocks comprise this Jurassic arc, which is one of only two arcs on Earth where the ancient Moho, separating upper mantle rocks from lower crustal rocks, is visible at the surface [ Burns , ; Mehl et al , ]. Furthermore, the subsurface expression of the arc is manifest as the Southern Alaska Magnetic High [ Saltus et al , ].…”

Section: Introductionmentioning

confidence: 99%

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Seismic velocity structure and anisotropy of the Alaska subduction zone based on surface wave tomography

Wang

Tape

2014

JGR Solid Earth

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Southcentral Alaska is a complex tectonic region that transitions from subduction of Pacific crust to flat slab subduction—and collision—of overthickened Yakutat crust. Because much of the Yakutat crust has been subducted, seismic imaging is needed in order to understand the crustal and upper mantle structural framework for this active tectonic setting. Here we use teleseismic Rayleigh waves to image large‐scale variations in shear wave structure. Our imaging technique employs a two‐plane wave representation with finite frequency sensitivity kernels. Our 3‐D isotropic model reveals several features: the subducting Pacific/Yakutat slab, slow wave speeds characterizing the onshore Yakutat collision zone, slow wave speeds of the Wrangell subduction zone, and a deep tomographic contrast at the eastern edge of the Pacific/Yakutat slab. We produce anisotropic phase velocity maps that exhibit variations in the fast direction of azimuthal anisotropy. These maps show the dominance of the Yakutat slab on the observed pattern of anisotropy. West of the Yakutat slab the fast directions are approximately aligned with the plate convergence direction. In the region of the Yakutat slab the pattern is more complicated. Along the margins of the slab the fast directions are roughly parallel to the margins. We identify notable differences and similarities with published SKS splitting measurements. Integrative modeling using 3‐D anisotropy models and different seismic measurements will be needed in order to establish a detailed 3‐D anisotropic velocity model for Alaska. This study provides a large‐scale starting point for such an effort.

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Section: Methodssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Seismic velocity structure and anisotropy of the Alaska subduction zone based on surface wave tomography

Wang

Tape

2014

JGR Solid Earth

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“…The fault zone extends through mainly unmapped Wrangellia terrane [64,65]. The large S Alaska magnetic high correlates with the Wrangellia terrane [66]. Based on magnetic data [67], the fault is regionally recognized as a 10± km wide zone with a WSW orientation along the NW margin of this large S Alaska magnetic high (Fig.…”

Section: Montana Creek Slice Faultmentioning

confidence: 99%

The Active Yakutat (Kula?) Plate and Its Southcentral Alaska Megathrust and Intraplate Earthquakes

Reeder¹

2016

JEASE

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Alaska geology and plate tectonics have not been well understood due to an active Yakutat plate, believed to be part of the remains of an ancient Kula plate, not being acknowledged to exist in Alaska. It is positioned throughout most of southcentral Alaska beneath the North American plate and above the NNW subducting Pacific plate. The Kula? plate and its eastern spreading ridge were partially "captured" by the North American plate in the Paleocene. Between 63 Ma and 32 Ma, large volumes of volcanics erupted from its subducted N-S striking spreading ridge through a slab window. The eruptions stopped at 32 Ma, likely due to the Pacific plate flat-slab subducting from the south beneath this spreading ridge. At 28 Ma, magmatism started again to the east; indicating a major shift to the east of this "refusing to die" spreading ridge. The captured Yakutat plate has also been subducting since 63 Ma to the WSW. It started to change to WSW flat-slab subduction at 32 Ma, which stopped all subduction magmatism in W and SW Alaska by 22 Ma. The Yakutat plate subduction has again increased with the impact/joining of the coastal Yakutat terrane from the ESE about 5 Ma, resulting in the Cook Inlet Quaternary volcanism of southcentral Alaska. During the 1964 Alaska earthquake, sudden movements along the southcentral Alaska thrust faults between the Yakutat plate and the Pacific plate occurred. Specifically, the movements consisted of the Pacific plate moving NNW under the buried Yakutat plate and of the coastal Yakutat terrane, which is considered part of the Yakutat plate, thrusting WSW onto the Pacific plate. These were the two main sources of energy release for the E part of this earthquake. Only limited movement between the Yakutat plate and the North American plate occurred during this 1964 earthquake event. Buried paleopeat age dates indicate the thrust boundary between the Yakutat plate and North American plate will move in about 230 years, resulting in a more "continental" type megathrust earthquake for southcentral Alaska. There are, therefore, at least two different types of megathrust earthquakes occurring in southcentral Alaska: the more oceanic 1964 type and the more continental type. In addition, large "active" WSW oriented strike-slip faults are recognized in the Yakutat plate, called slice faults, which represent another earthquake hazard for the region. These slice faults also indicate important oil/gas and mineral resource locations.

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“…The regional distribution of arcuate magnetic domains (Figure d) and gravity anomalies, and their boundaries, match well to the different accreted terranes separated by these major faults [ Glen et al ., ; Saltus et al ., ]. In the southern part of the region, the Southern Alaska magnetic high correlates with intensely magnetic, but variable, dominantly mafic rocks of the WCT.…”

Section: Tectonic Backgroundmentioning

confidence: 99%

“…An abrupt south to north drop in magnetic potential as well as in the gravity signature occurs across the Talkeetna suture zone, from the Southern Alaska magnetic high to the Southern Alaska magnetic trough [ Glen et al ., ]. The Southern Alaska magnetic trough coincides largely with the ARSZ where transitional crust is less dense and weakly magnetic beneath Mesozoic flysch basins [ Saltus et al ., ].…”

Section: Tectonic Backgroundmentioning

confidence: 99%

Alternating asymmetric topography of the Alaska range along the strike‐slip Denali fault: Strain partitioning and lithospheric control across a terrane suture zone

et al. 2014

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Contrasting lithospheric strength between terranes often results in the concentration of strain and deformation within the weaker material. Dramatic alternating asymmetric topography of the central and eastern Alaska Range along the active Denali fault is due to contrasting lithospheric strength between terranes and a suture zone, controlled by fault location with respect to the irregular boundary of a relatively stronger terrane backstop. Highest topography and greatest Neogene exhumation in the central Alaska Range occur on the concave side of the arcuate Denali fault, yet to the north and on the convex side of the fault in the eastern Alaska Range. The Denali fault largely lies along a Mesozoic suture zone between two large composite terranes (Yukon and Wrangellia composite terranes: YCT and WCT), but the McKinley strand of the fault cuts across an embayment of weaker suture-zone rocks (Alaska Range suture-zone, ARSZ) within the irregular southern boundary of the YCT (Hines Creek fault). Deformation (and uplift of the Alaska Range) is driven by slip and partitioning of strain along the Denali fault, occurring preferentially in weaker rocks of the ARSZ against the stronger YCT. Where the YCT lies well north of the McKinley strand, deformation is primarily to the north of the fault (eastern Alaska Range). Where the YCT is close to the fault, deformation is primarily to the south (central Alaska Range). While the trace of the McKinley strand approximates a small circle, two restraining bends (McKinley and Hayes) pinned equidistant from the ends of this strand localize uplift and exhumation.

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The geophysical character of southern Alaska—Implications for crustal evolution

Cited by 25 publications

References 32 publications

Seismic velocity structure and anisotropy of the Alaska subduction zone based on surface wave tomography

Seismic velocity structure and anisotropy of the Alaska subduction zone based on surface wave tomography

The Active Yakutat (Kula?) Plate and Its Southcentral Alaska Megathrust and Intraplate Earthquakes

Alternating asymmetric topography of the Alaska range along the strike‐slip Denali fault: Strain partitioning and lithospheric control across a terrane suture zone

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