Tectonic Evolution of the Western Brooks Range Fold and Thrust Belt, Alaska

Jose de Vera and Ken McClay
Fault Dynamics, Research Group, Royal Holloway, University of London, Egham, Surrey, United Kingdom

The western Brooks Range fold and thrust belt of Alaska exposes a telescoped Late Devonian through Jurassic continental rifted margin, now preserved as a stack of NE-SW-trending, NW-verging, internally imbricated and regionally folded allochthon thrust sheets. These were emplaced as a result of arc-continent collision during the Middle/Late Jurassic-Late Cretaceous Brookian orogeny and subsequently uplifted by late tectonic activity in the Tertiary. The fold an thrust belt consists of seven tectonostratigraphically distinct thrust sheets or allochthons, each representing a distinct part of the ancient continental margin. The thrust sheet stack is separated from relatively undeformed strata of the North Slope foreland basin by a well-developed thrust front, whose position, orientation, vergence and structural styles vary significantly along-strike. These changes are best represented by the Wulik Peaks transverse zone, a regional-scale feature along which the thrust front trends at a high angle to the dominant NE-SW-trending structural grain of the fold and thrust belt. Integration of structural, stratigraphic, and geophysical data suggests that the along-strike changes in the geometry and position of the thrust front and the development of the Wulik Peaks transverse zone resulted from the inheritance in the Early Cretaceous of Late Devonian to Jurassic WNW-ESE- to NW-SE-trending extensional faults of the ancient continental margin. WNW-ESE-trending Tertiary (Eocene) to present-day extensional faults record extensional reactivation of the Wulik Peaks transverse zone and close a remarkable cycle of Late Devonian to Present Day inheritance of WNW-ESE- to NW-SE-trending fault systems.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas