Research - Alaska

Tectonic evolution of the Alaska Range

The Alaska Range is located ~500 km inland of the active southern Alaskan margin. The central Alaska Range is bounded on its northern margin by the transpressive strike-slip Denali Fault system (DFS) and contains peaks in excess of ~ 6000 m (Mt. McKinley). The eastern Alaska Range is located farther east along the DFS and occurs near the junction between the Hines Creek strand of the DFS located to the north of the range and the main strand located to the south. The high topography of the eastern Alaska Range is located mainly to the north and includes peaks such as Mount Nenana.

Alaska Map1
Figure 1. DEM of the Alaska Range (flooded to 1000 m). Inset: Tectonic map of southern Alaska, red dashed line is the outline of the subducted Yakutat slab (thanks to Jeff Benowitz for compiling this figure)

Deformation along the DFS is driven by plate tectonic processes ~500 km to the south where subduction of the Pacific plate is occurring. The Yakutat microplate, a composite oceanic/continental terrane is actively undergoing both subduction and collision, with the latter increasing toward the eastern margin. The Yakutat microplate is moving parallel to the Fairweather Fault at ~46-52 mm/yr.  Collision of the Yakutat has resulted in deformation in southern Alaska south of the DFS, accommodated mostly as thrusting and uplift of the Logan-St Elias coastal orogen. The Yakutat terrane has been thrust under Alaska to a depth of ~140 km and extends as far as 600 km north of the trench. The recent imaging of the Yakutat slab under Alaska and discovery that it is buoyant and well-coupled to the lithosphere suggests that this slab may be responsible for deformation into central Alaska.

alaska map2
Figure 2. Regional geological map of central Alaska. High topography within the central Alaska Range is located mainly to the south of the DFS whereas high topography within the eastern Alaska Range is located to the north at the junction between the DFS and the Talkeetna thrust fault.

Research Objectives

To apply low-temperature thermochronology to the Alaska Range to constrain the patterns of denudation and hence constrain the tectonic evolution of the region and driving mechanisms for deformation along the fault.  We are working in the central Alaska Range and also the eastern Alaska Range with collaborators Jeff Benowitz and Paul Layer (University of Alaska, Fairbanks) and Sarah Roeske (University of California, Davis).

In the central Alaska Range we are applying (U-Th)/He on apatite separates from our previous samples, including a 4 km vertical profile from the western flank of Denali. Just north of the DFS we are using detrital thermochronology on sediments of the Nenana Gravel and Usibelli Group.  Deposition of the Nenana Gravel is related to the erosional unroofing of the Alaska Range.

In the eastern Alaska Range we are applying low-temperature thermochronology (apatite fission track) to basement samples.  Jeff Benowitz and Paul Layer are doing the 40Ar/39Ar on those same samples and Sarah Roeske is undertaking detailed structural and petrographic analysis along the DFS.

Various tectonic factors have been related to uplift and subsequent denudation and/or exhumation of rocks in the Alaska Range including:
1) The change in relative plate motion of the Pacific plate
2) Strain-partitioning along the DFS
3) Collision of the Yakutat terrane
4) Variations in crustal root thickness as a consequence of the subduction of a buoyant slab 5) Coupling of the buoyant Yakutat slab
6) Rotation of the southern Alaskan microplate

Alaska Data

Figure 3. A compilation of thermochronology data for the central Alaska Range from the Syracuse Group and the University of Alaska showing multiple cooling (denudation events). AFT data from Denali showing (a) onset of rapid cooling at ~6 Ma and (b) denudation/rock uplift patterns since ~6 Ma. (c) AFT and 40Ar/39Ar data (courtesy of Jeff Benowitz) from Denali.

Field images

Alaska ridge
Stephanie Perry and Jeff Benowitz hiking along a ridge-top of unconsolidated interbedded gravel and sand within the Pliocene Nenana Gravel, Suntrana Creek, south-central Alaska (Photo Paul Fitzgerald).
Small engine plane on glacier
Jeff and Stephanie on the Black Rapids Glacier, eastern Alaska Range – ready to collect more samples (Photo Paul Fitzgerald)
Mt. Hayes
Mt Hayes in the eastern Alaska Range (Photo: Jeff Benowitz)
Mt. Hayes
Denali (20,320') from the western end of the Alaska Highway (Photo: Paul Fitzgerald)

Contact Us

Department of Earth Sciences
204 Heroy GL
Ph: 315-443-2672
Fx: 315-443-3363

Thermochronology Lab