T230 Tectonic Development of the Northern North American Cordillera

Wednesday, 12 October 2011
8:00 AM - 12:00 PM
Room 200DE

THE TOPOGRAPHICALLY ASYMMETRICAL ALASKA RANGE: MULTIPLE TECTONIC DRIVERS THROUGH SPACE AND TIME

Paper number: T230-5
Program: Technical Sessions
Time: 9:05 AM – 9:20 AM

Authors

Abstract

The topographically segmented ~700 km long Alaska Range evolved over the last ~50 Ma in response to both far-field driving mechanisms and near-field boundary conditions. To the east, the eastern Alaska Range follows the curve of the Denali Fault strike-slip system forming a large arc of high topography across southern Alaska. The majority of the topography in the eastern Alaska Range lies north of the Fault. A large gap of low topography separates the eastern Alaska Range from the central Alaska Range where the majority of high topography lies to the south of the Denali Fault. Further west in the Mt McKinley area, the Denali fault forms a restraining bend and the high topography remains south of the fault. Southwest of the bend, the north-south trending western Alaska Range takes an abrupt 90 degree turn away from the Denali Fault.

We apply new and existing U-Pb, 40Ar/39Ar, apatite fission track and (U-Th)/He thermochronology to further constrain the thermal and exhumation history of the entire Alaska Range. Cooling and exhumation patterns are combined with information from nearby Tertiary basins to further constrain the temporal and spatial patterns of mountain building along the Denali fault.

Periods of mountain building within the Alaska Range are related to Paleocene-Eocene ridge subduction and the lasting thermal effects of an associated slab window (~50 Ma to ~35 Ma), Neogene flat-slab subduction of the Yakutat microplate (~24 Ma to present), Yakutat microplate latitudinal variation in thickness (~6 Ma to present), block rotation/migration, and fault reorganization along the eastern segments of the Denali Fault System. However, it is clear from basin, petrological and thermochronological constraints that not all of the far-field driving mechanisms affected every segment of the Alaska Range to the same degree or at the same time. Alaska Range tectonic reconstruction is also complicated by near-field structural controls (e.g., fault geometry) on both the timing and extent of deformation. Fault geometry affects both the amount of exhumation (e.g., >14 km in the Susitna Glacier region eastern Alaska Range) and location of topographic development (e.g., north or south of the Denali Fault). The current geomorphology has been modified by Plio-Quaternary (~3 Ma to present) surface processes, notably glacial processes.