Map Showing Nature and Distribution of Faults in Northern Alaska
A map showing the nature and distribution of surface traces of faults in northern Alaska was constructed at a scale of 1/2,500,000 from published and unpublished map sources, seismic data, and satellite images as a contribution to the new Geologic Map of the Arctic of the International Polar Year project. The primary structural elements of the map area are the east-west-trending, north-vergent Brooks Range orogenic belt and its undeformed autochthon which lies to the north. Faults in the orogen are divided according to age and deformational style into five catagories:
1. Thrust faults of Early Cretaceous age typically are low-angle faults that represent the hanging wall flats beneath local to regional allochthons formed during north-vergent thin-skinned collisional deformation. The Cretaceous thrusts are pervasive in the axial part of the Brooks Range.
2. Reverse and thrust faults of Tertiary age represent the emergent part of a deep-seated Tertiary retroarc thrust system that cut Early Cretaceous thrust faults. The Tertiary faults have reverse geometry near the range front and thrust geometry farther north, culminating in a regional passive-roof duplex system (delineated by south-vergent faults on the map) developed in Cretaceous foreland basin strata. Reverse faults are also are common in the eastern Brooks Range where they underlie large north-vergent basement-involved imbricates and duplexes that uplift and form the northeastern salient of the Brooks Range.
3. Down-to-the-south extensional faults formed during the Albian and Late Cretaceous compose an extensive system of ductile to brittle faults along the southern margin of the Brooks Range. This zone probably represents the northern limit of structures related to regional orogenic collapse in central Alaska.
4. Strike-slip faults of post-Jurassic age bound the southeastern and southern Brooks Range and the eastern Lisburne Hills. The right-slip Kobuk fault system may have reoccupied the extension fault zone in the southern Brooks Range. The age and tectonic origin of the steep north-trending fault in the eastern Lisburne Peninsula is uncertain but it may have undergone right-lateral displacement in the Upper Cretaceous or Tertiary.
5. Tertiary normal faults deform earlier formed structures in the western and central Brooks Range and probably are related to extension in the coeval Hope Basin in the Chukchi Sea to the west.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009