Upper plate proxies for flat-slab subduction processes in southern Alaska

Finzel, Emily S.; Trop, Jeffrey M.; Ridgway, Kenneth D.; Enkelmann, Eva

doi:10.1016/j.epsl.2011.01.014

Cited by 128 publications

(165 citation statements)

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“…16.1; Finzel et al, 2011). The eastern region in northwestern Canada and eastern Alaska is characterized by volcanism in the Wrangell volcanic belt (WVB on Fig.…”

Section: Oligocene To Holocene Subduction Of Thick Oceanic Crust Intrmentioning

confidence: 99%

Modification of Continental Forearc Basins by Flat‐Slab Subduction Processes: A Case Study from Southern Alaska

Ridgway

Trop

Finzel

2011

Tectonics of Sedimentary Basins

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Forearc basins are large sediment repositories that develop in the upper plate of convergent margins and are a direct response to subduction. These basins are part of the magmatic arc-forearc basin-accretionary prism "trinity" that defines the tectonic configuration of the upper plate along most subduction-related convergent margins. Many previous studies of forearc basins have explored the links between construction of magmatic arcs, exhumation of accretionary prisms, and sediment deposition in adjacent forearc basins. These studies provide an important framework for understanding firstorder tectonic processes recorded in forearc basins that are characterized by long-lived subduction of "normal" oceanic crust. Many convergent margins, however, are complicated by second-order subduction processes, such as flat-slab subduction of buoyant oceanic crust in the form of seamounts, spreading and aseismic ridges, and oceanic plateaus. These second-order processes can substantially modify the tectonic configuration of the upper plate both in time and space, and produce sedimentary basins that do not easily fit into the conventional magmatic arc-forearc basin-accretionary prism trinity.In this chapter, we discuss the modification of the southern Alaska forearc basin by Paleocene-Eocene subduction of a spreading ridge followed by OligoceneHolocene subduction of thick oceanic crust. This thick oceanic crust is currently being subducted beneath south-central Alaska and has an imaged maximum thickness of 30 km at the surface and 22 km at depth. Findings from southern Alaska suggest that forearc basins modified from flat-slab subduction processes may contain a sedimentary and volcanic stratigraphic record that differs substantially from typical forearc basins. Processes and sedimentary features that characterize modified forearc basins include the following: (1) flat-slab subduction of a buoyant, topographically elevated spreading ridge oriented subparallel to the margin prompts diachronous uplift of the forearc basin floor and exhumation of older marine forearc basin strata as the ridge is subducted. Passage of the spreading ridge leads to subsidence and renewed deposition of nonmarine sedimentary and volcanic strata that locally exceeds the thickness of the underlying marine strata. (2) Insertion of a slab window beneath the forearc basin during spreading ridge subduction produces local intrabasinal topographic highs with adjacent depocenters, as well as discrete volcanic centers within and adjacent to the forearc basin. (3) Flat-slab subduction of thick oceanic crust also results in surface uplift and exhumation of forearc basin sedimentary strata. However, the insertion of thick crust throughout the flat-slab region (i.e., lack of a slab window) inhibits subduction-related magmatism adjacent to the forearc basin. In the case of subduction of a >350-km-wide fragment of thick oceanic crust beneath south-central Alaska, exhumation of forearc basin strata located above the region of flat-slab subduction has prompted enhanced T...

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“…16.1; Finzel et al, 2011). The eastern region in northwestern Canada and eastern Alaska is characterized by volcanism in the Wrangell volcanic belt (WVB on Fig.…”

Section: Oligocene To Holocene Subduction Of Thick Oceanic Crust Intrmentioning

confidence: 99%

Modification of Continental Forearc Basins by Flat‐Slab Subduction Processes: A Case Study from Southern Alaska

Ridgway

Trop

Finzel

2011

Tectonics of Sedimentary Basins

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“…These plutons were then shut off underneath by the oblique NNW flat-slab subducting PAC from the S. The subducted KULA-RESUR? spreading ridge volcanic extrusions then ended 35.5 Ma and also the subduction related magmatism by YAK ended about 32 Ma for southcentral Alaska, both caused by this oblique NNW flat subducting PAC extending underneath YAK [26]. But, this new NNW subducting PAC left the region to the E unsubducted.…”

Section: David Publishingmentioning

confidence: 99%

“…This PAC rotation turned off subduction magmatism at 43 Ma in E Alaska, leaving a large block of underplated oceanic crust and mantle of RESUR? [16,26]. In the Prince William Sound (PWS, Fig.…”

Section: David Publishingmentioning

confidence: 99%

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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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“…Subduction of the Yakutat microplate started in the late Eocene-early Oligocene, causing the magmatism on the North American Plate to shut off, building topography, and causing rock exhumation in the region above the flat slab, and basin subsidence around the perimeter (fig. 4.3.1;Finzel et al, 2011). The thick Yakutat slab has been imaged to reach 650 km inboard from the present-day collisional front to the Alaska Range (Ferris et al, 2003) (fig.…”

Section: The St Elias Mountain Rangementioning

confidence: 99%

Seismic and non-seismic influences on coastal change in Alaska--Fieldtrip guide and conference abstracts, 5th International Conference of IGCP 588

Barlow¹,

Koehler²

2015

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Upper plate proxies for flat-slab subduction processes in southern Alaska

Cited by 128 publications

References 73 publications

Modification of Continental Forearc Basins by Flat‐Slab Subduction Processes: A Case Study from Southern Alaska

Modification of Continental Forearc Basins by Flat‐Slab Subduction Processes: A Case Study from Southern Alaska

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

Seismic and non-seismic influences on coastal change in Alaska--Fieldtrip guide and conference abstracts, 5th International Conference of IGCP 588

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